CN102753664A

CN102753664A - Electrically and/or thermally conductive suspensions including graphite microfluids

Info

Publication number: CN102753664A
Application number: CN2010800639195A
Authority: CN
Inventors: 郑瑞廷; 高进伟; 陈刚
Original assignee: Massachusetts Institute of Technology
Priority date: 2009-12-15
Filing date: 2010-12-15
Publication date: 2012-10-24
Anticipated expiration: 2030-12-15
Also published as: WO2011084481A1; CN102753664B

Abstract

Fluids comprising graphite particles and related methods are generally described. In some embodiments, "microfluids" are described. Generally, the microfluids can comprise a fluid and a plurality of graphite particles with microscale dimensions. Articles, systems, and methods involving the control of thermal and/or electrical conductivity in suspensions are also generally described.

Description

The electricity that comprises the graphite microfluid is led and/or thermal conductance suspension-s

Related application: the application requires the Patent Application No. 12/638135 of application on December 15th, 2009, and patent name is that the right of priority of the USP of graphite microfluid also is its part continuation case; The application also requires the Patent Application No. 12/720382 of on March 9th, 2010 application, patent name be the control that thermal conductance and/or electricity are led in the suspension-s USP right of priority and be its part continuation case; Two applications are all quoted and are incorporated in this patent.

Government-funded: the present invention receives American National natural science fund (No.CBET-0506830) and subsidizes.Government has established right for the present invention.

Technical field

This patent has related in general to the fluid and relevant preparation method that comprises graphite granule.This patent has also related generally to this fluid thermal conductance of control and electric product, system and the preparation method who leads in suspension-s.

Background technology

A lot of industry and business system, power station for example, car engine and microelectronic system all need efficiently radiates heat to obtain the optimum operation effect.The tradition intensifying heat transfer generally is employed in and enlarges contact area (for example fin) in the system and increase the hot-fluid flow velocity.Yet traditional heat dissipating method many times can't be realized high efficiency and heat radiation.Nearest research has obtained a kind of high heat-conducting fluid.This fluid is exactly a kind of highly heat-conductive material that in the fluid of relative low thermal conductivity, suspends.This fluid is except providing enough thermal conduction, and this fluidic can significantly reduce the size of heat exchanger in low thermal conductivity requirement system.

Prepare this high heat-conducting fluid and have certain degree of difficulty.For example in a lot of instances, in some heat exchangers, be difficult to prepare a kind of stable high heat conduction suspension-s.Simultaneously, some material, as, the suspension-s material of some nanoscales is difficult to obtain sufficiently high thermal conductivity hot-fluid.More crucial is that a lot of highly heat-conductive materials are because the daily use of the very high very difficult realization of its price.

Can control thermal conductance and/or electricity and lead, for example heating and refrigeration system, electric power distribution, sensing etc. having good application prospects in a lot of fields.The preparation of high heat conduction and conductive fluid has been accomplished in recent research.This type fluid can be through suspending high heat conduction and/or high conductive material in low relatively heat conduction and conductive fluid.In case solid particulate is suspended in certain fluid usually, the heat conduction of suspension-s and conductivity no longer change with regard to being fixed.Have the needs to this system in the daily use, this suspension-s need not led and thermal conductivity through adding the electricity that other any materials just can change self.

Summary of the invention

The invention provides a kind of fluid of graphite granule and common method of preparation thereof of comprising.The present invention has also proposed thermoelectric and/or electric product, system and the method for leading control in the suspension-s.

Microfluid has been described in one embodiment.In some scheme, microfluid comprises a kind of hydrophobic fluid and a large amount of graphite granules, and the average largest cross-sectional sized of graphite granule is about 500 nanometers to 10 micron.In some scheme, graphite granule can be in fluid stable suspersion, and need not carry out functional group and handle at graphite surface.

In certain embodiments, this microfluid comprises a kind of in two kinds of fluids of water and alcohol, and a large amount of average cross-section yardstick is the graphite flake of about 500 nanometers to 10 micron.Graphite flake can form steady suspension in fluid.

In certain embodiments; This microfluid comprises a kind of liquid and a large amount of graphite flake, and the flakiness ratio of these graphite flakes is at least 10:1, and average largest cross-sectional sized is about 500 nanometers to 10 micron; Graphite flake can be in fluid stable suspersion, need not introduce any functional group on the graphite flake surface.

In other embodiments, a kind of method has been described.In some cases, this method comprises a large amount of graphite flake of interpolation in fluid, the average largest cross-sectional sized of graphite flake for greatly about between 500 nanometers to 10 micron, graphite flake can be in fluid stable suspersion, any functional group need not induce one on the graphite flake surface.This method has further comprised the stable graphite granule suspension-s of formation in fluid.

This method also comprises, in some cases, a kind of particulate fluid that comprises is provided, and the freezing formation of fluid is comprised the polycrystalline solid of crystal grain and crystal boundary; In certain embodiments, wherein most of particulate largest cross-sectional sized are less than 10 microns, and in some cases, particle thermal conductivity at least one direction when measuring for 25 ℃ is at least 5W/mK and/or specific conductivity is at least 10S/m; In some cases, in freezing step, the part particle in the fluid is towards the zone migration of crystal boundary at least, and the granule density that is formed on the crystal boundary place is higher than at crystal grain inner.

In some cases, this method comprises provides the suspension medium that comprises first phase and the particle in suspension medium; Apply thermal gradient and/or electromotive force at the suspension-s two ends and allow suspension medium that the phase transformation of first to second phase takes place, make the thermal conductivity of suspension-s and/or specific conductivity change thus.

Advanced and the novel feature of other of this patent will be below the detailed description of each non-limiting example in particular embodiment.

Description of drawings

Will be among the unrestricted embodiment of the present invention through example and description of drawings, accompanying drawing is a synoptic diagram, does not represent physical size.In these figure, any identical or approximately uniform part is all passed through a numeral.For the sake of clarity, not that each part all marks in every figure, each part in neither inventing among each embodiment is all listed, because have the people of conventional knowledge not need synoptic diagram to understand the present invention for this area.Among these figure:

Fig. 1 comprises the microstructure synoptic diagram example of a graphite flake;

Fig. 2 comprises the preceding optics picture of graphite granule cleavage of one 30 * amplification according to an embodiment;

Fig. 3 comprises a cleavage graphite exemplary scanning Electronic Speculum (SEM) displaing micro picture;

Fig. 4 has comprised the synoptic diagram of graphite granule according to one group of instance;

Fig. 5 A-5B comprises the model experiment graphic representation of thermal conductivity and graphite concentration;

Fig. 6 comprises the model experiment graphic representation of specific conductivity and graphite concentration according to one group of instance;

Fig. 7 A-7C comprises the synoptic diagram of suspension-s phase transition process according to one group of embodiment;

Fig. 8 A-8E comprises the SEM picture of (A) typical graphite flake; (B) typical graphite flake TEM picture; (C) the high resolution TEM picture of regional a in the graphite flake among Fig. 8 B; (D) concentration is the typical optics displaing micro picture of 0.2%V/V graphite suspension; (E) concentration is preserved a month later typical photo for the 0.2%V/V graphite suspension;

Fig. 9 A-9G comprises the specific conductivity of the suspension-s that (A) graphite volume(tric)fraction is different and the model experiment curved line relation of temperature; (B) the model experiment curved line relation of graphite flake volume(tric)fraction in conductivity variations rate and the suspension-s; (C) the model experiment curve relation figure of the thermal conductivity of the suspension-s of different graphite flake volume(tric)fractions and temperature.(D) the model experiment graphic representation of suspension-s conductivity variations rate and graphite flake volume(tric)fraction; (E) volume(tric)fraction is the typical optics picture of 0.05% graphite/n-Hexadecane suspension-s; (F) graphite that freezes/n-Hexadecane suspension-s and the typical optics picture that (G) melts later graphite/n-Hexadecane suspension-s once more.

Figure 10 is according to one group of embodiment, the synoptic diagram of the platform of contact resistance experiment test; And

Figure 11 A-11C comprises that (A) explains the canonical schema that contact area changes between the particle; (B) the model experiment graphic representation of resistance and temperature; (C) freeze typical pressure distribution plan in the n-Hexadecane.

Embodiment

Regard to the fluid that comprises graphite granule down and carry out general description with relevant method." microfluid " described in certain embodiments.In general, microfluid comprises a kind of fluid and numerous micro-meter scale graphite granule.Graphite granule can be suspended in the fluid.The inventor has been found that the particle of micro-meter scale, rather than the particle of nanoscale, more can improve the fluidic heat transfer potential and improve fluidic stability.(for example graphite flake is suspended in the hydrophobic fluid in certain embodiments; In oil); Graphite flake can form steady suspension in fluid, need not introduce other functional groups (for example phenyl and carboxyl) on the graphite flake surface, does not use any tensio-active agent and other stablizers.In addition graphite flake can stable suspersion at water seeking liquid, for example in water and the ethanol.This microfluid has a lot of purposes, is included in and is used as heat transferring medium in the heat exchanger.This microfluid also can be used as the conductivity medium.

Fig. 1 is the synoptic diagram of graphite granule microtexture, can be used among the relevant embodiment.

In general, the structure of graphite flake comprises multilayer (12,14 and 16) Graphene.Every layer graphene comprises the carbon atom that hexagonal lattice is arranged.And combine through typical Van der Waals force with adjacent graphene layer, though the existence of a small amount of covalent linkage is arranged.In certain embodiments, the surface of Graphene can be oxidized, in some cases, part hydrophilic group at least can be provided.For example, in some cases, the graphite granule total hydrophilic that can become, perhaps, graphite granule can become have amphiphilic.

In general, effectively heat conduction and conduction of graphite.In some cases, having good electricity with respect to second each and every one direction (perpendicular to first direction) graphite granule in first direction (for example, direction in the face) leads and thermal conductance.These graphite granules are called as anisotropic conductor.First direction is the more effectively direction of conduction, just a particulate length direction (direction that is parallel to the Graphene lamella) of electricity/heat.Second direction is the lower direction of electricity/efficiency of thermal transfer, is exactly particulate thickness direction (cross-sectional direction of graphite).In certain embodiments, the size of first direction of particulate is greater than the size of second direction, and these particles are had conductivity in the very high face by weighing-appliance.

Graphite also is a kind of super lubricant.Super lubricating is a kind of phenomenon known in the art, and it is approaching to refer generally to two planar frictional force, but do not reach zero.In microfluid super lubricant for example the use of graphite can effectively make the frictional force in the microfluid keep a very low value.The low-frictional force fluid can reduce the damage to moving parts surface in the equipment simultaneously through low relatively that pump power realizes that fluidic effectively circulates.In addition, low friction, high heat-conducting fluid can both need the also occasion realization dual-use of the high heat transfer of needs of effectively lubricating.Do not hope to receive the restriction of any theory, the super lubrication of graphite comes from interlayer magnetism lower in the graphite (for example, Van der Waals force).

Graphite granule can be made up of a lot of graphite that are fit to type.In certain embodiments, graphite granule can comprise or prepare from natural graphite.Fig. 2 has provided and has amplified 30 times typical graphite optics picture.Natural graphite has a lot of forms, and in certain embodiments, natural graphite comprises kish sheet (being often referred to flake graphite).In general, flake graphite is with isolated flat, and dish shape particle exists.If be kept perfectly, have six side borders, have irregular or the horn shape border after destroying.In some cases, natural graphite comprises amorphous graphite (also being the carbonization hard coal), and this also is usually our said graphite.Its graphite granule comes from the rotten of coal, and exists with tiny particle.Usually call amorphous state to very tiny flake graphite in this area.In addition, natural graphite comprises blocky graphite (referring to vein graphite), and it usually occurs in crack mineral ore or breaks, exists with the micro-or acicular crystalline aggregate of a large amount of endogenous.

In some cases, graphite granule can comprise or processed by synthetic graphite.The example of synthetic graphite comprises, high order pyrolytic graphite (HOPG), electrographite and analogue.In certain embodiments, graphite granule comprises or above two or more types compositions.

In certain embodiments, graphite granule comprises cleavage graphite.Fig. 3 is the electron microscope picture of typical cleavage graphite among one group of embodiment.Provide the method for this cleavage graphite of preparation below.In certain embodiments, the volume of cleavage graphite can be realized minimum 10 times, 50 times, and 100 times, 300 times, perhaps at least 500 times of expanding to original volume.Corresponding, the density of expanded graphite can reduce at least 10 times, and 50 times, 100 times, 300 times, perhaps at least 500 times to the density of its initial graphite granule (being graphite flake).

Graphite granule described herein comprises high-load relatively carbon (perhaps 99.9wt% at least, wt is a mass parts for 95wt% at least, 99wt% at least), and the measurement of carbon content does not comprise the functional group above it, can further set forth below.In some cases, graphite granule can comprise one or more impurity (like metal, alloying element) (for example, the situation of intercalated graphite) in lattice.The example of an intercalated graphite comprises potassium graphite (KC8) and calcium graphite (CaC8) and other similar situation.Intercalated graphite has superconduction ability (can reach zero resistance).

Though the embodiment has here mainly described the use of graphite granule, should be noted that the present invention is not limited to this.In certain embodiments, this microfluid also comprises the particle of the material with high thermal conductivity coefficient that some are suitable.In some instances, these particles comprise base plane cleavage crystal material.It is a kind of this area common phenomena that base dissociates, and refers generally to the crystal cleavage surface and is parallel to base plane.These materials include, but are not limited to mica (blotite for example, white mica, phlogopite, lithionite, margarite; Glaukonine etc.), clay mineral matter (kaolinite for example, illite, polynite, smectite; Vermiculite, talcum, magnalium skin stone, pyrophyllite, etc.) and other materials.

In certain embodiments, graphite granule is a micro-meter scale.The selection of graphite size is all important to the raising of graphite microfluid stability and fluidic heat conductivility, for example, relative centimetre of perhaps big scale particle more, the micron-scale particle suspends in fluid easily.In addition, micro-meter scale suspension-s is not easy the blocking heat-exchanger pipeline.At some is among the embodiment, and the average largest cross-sectional sized of micron graphite particulate is between 500 nanometers and 10 microns, between 1 micron to 5 microns, or between 1 micron to 10 microns.Here the ultimate range between two borders of single structure that " cross-sectional dimension " refers to test.For example, graphite granule 20 has width 22 and thickness 24 in Fig. 4.The maximum cross section is 26.The average cross-sectional dimension of particulate is meant the mean number of these particle cross-sectional dimension.The scanning electron microscopy picture (SEM) that a domestic method of the size of test largest particle xsect is an analysing particulates.

Among some embodiment, the yardstick of the graphite of high relatively per-cent is a micron order in the microfluid.For example, in certain embodiments, volume(tric)fraction is at least 80%, 90%, 95%, and perhaps the xsect of 99% graphite granule is between 500 nanometers to 10 micron, between 1 micron to 10 microns, perhaps between 1 micron to 5 microns.

In certain embodiments, used graphite granule is a graphite flake.In general, the characteristic of graphite flake is that its thickness (vertical in fact graphene film directional survey) is significantly less than horizontal (parallel in fact graphene film directional survey) size.In certain embodiments, the flakiness ratio of this graphite flake (ratio of maximum transversal yardstick and maximum ga(u)ge just) was at least 10: 1, was at least 50: 1, was at least 100: 1, was at least 500: 1, perhaps was at least 1000: 1.

In certain embodiments, other shapes graphene-based particle of this microfluid except that sheet.This graphene-based particle possibly comprise, micron tube for example, perhaps formation such as micron cone.Should be noted that other shapes also possibly occur.Do not hope limited any theory, micron tube perhaps is that graphene film is owing to inner tensions is rolled formation with the micron awl.

In some instances, graphite granule described herein can functionalised and be with corresponding functional group.The people who has conventional technical ability in this area will be understood that the implication of phrase " functional group ".Functionalisation of surfaces does not comprise the surface (promptly let graphite be exposed in the oxygen, let the some or all of surface of graphite that oxidation takes place) of graphite oxide.In certain embodiments, the hydrophobic graphite granule can surface functionalization, becomes relative water-wetted surface, can stable suspersion at water seeking liquid, for example in water and the alcohol.For example, graphite granule can form hydroxy functional group after the oxidation.Graphite surface can the multiple functional group of functionalized formation, hydroxyl for example, carboxyl, epoxy group(ing) etc.The functionalization process on graphite granule surface is perhaps useful aspect the hydrophilic characteristics of regulating graphite surface, will do detailed description below.In certain embodiments (for example, when microfluid comprises water seeking liquid, for example water and ethanol), the functionalization graphite granule can improve the stability of graphite granule suspension-s, perhaps forms stable suspension, anyway form unstable suspension-s.

Microfluid described herein comprises the graphite granule of proper concn.In certain embodiments, the volume(tric)fraction of graphite granule is lower than 2%, is lower than 1%, and between 0.01% and 2%; 0.05% and 2%, between 0.1% and 2%, between 0.5 and 2%, between 1% and 2%; Between 0.01% and 1%, between 0.05 and 1%, between 0.1% and 1%; Between 0.5 and 1%, between 0.8% and 1%, perhaps between 0.9% to 1%.In certain embodiments, can prepare the graphite granule volume(tric)fraction not at the interval graphite microfluid of above concentration.A common technology in this field is to calculate the volume(tric)fraction of particle (for example, graphite granule) in the microfluid, for example, do such calculating, can measure the particulate quality.The particulate volume can calculate divided by pellet density through the quality of measuring.So volume(tric)fraction can be calculated divided by particle volume and medium volume sum through the particulate volume.

Any suitable fluid (that is liquid) can be used for preparing describes a micron fluid here.In certain embodiments, this microfluid comprises alcohol (for example, ethanol, terepthaloyl moietie etc.), water, the perhaps mixture of water and alcohol.In some instances, this microfluid comprises oil (for example, poly-alpha-olefin (PAO) oil, silicone oil, MO, synthetic oil, oxide glycol/propylene oxide synthetic oil gathers the synthetic wet goods of alkane glycol).In some instances, also possibly use other oils.The selection of base fluid type mainly depends on the service orientation of this microfluid.

In some cases, this microfluid comprises hydrophylic fluids (for example water and alcohol etc.).In certain embodiments, this microfluid comprises hydrophobic liquid (for example wet goods).In general, hydrophilic and hydrophobic refers to whether whether this liquid can form stable mixture with water under the entity effect about not having tensio-active agent or other stabilize water and liquid each other.

(for example when microfluid comprise hydrophobic liquid, oil) in some cases, graphite granule can lack under the situation of functional group's (for example phenyl, carbonyl etc.) stable suspersion in fluid on the surface.In some cases, graphite granule can be under the effect that does not have surface dispersant stable suspersion in this fluid.Under a situation, graphite granule not under all function of stabilizer in this fluid stable suspersion.Here stablizer is meant any entity that can improve graphite granule stability in suspension-s.Lack under the situation of stablizer graphite granule also can stable suspersion, but need be under identical adjusting (being temperature, pressure condition etc.).Typical stablizer comprises, tensio-active agent for example, acid, base material, the stable functional group of graphite surface (for example phenyl, carboxyl) etc.

For example, in certain embodiments, microfluid comprises the suspension-s of stable graphite granule, and graphite surface does not have functional group's (or/and tensio-active agent, or/and stablizer).In some instances, microfluid possibly comprise functional group's graphite granule (or/and tensio-active agent, or/and stablizer), but when not having these stablizers, graphite still can form stable suspension by stable suspersion.In some cases, perhaps the functional group of these graphite surfaces (or/and tensio-active agent, or/and stablizer) does not have materially affect to the suspension of graphite granule.In other cases, there are some effects in the functional group of graphite surface (or/and tensio-active agent, or/and stablizer) to the stability of suspension-s, but is not enough to form stable suspension owing to the appearance of these stablizers.A special case, microfluid can be suspended in oil (for example PAO oil) by graphite granule and constitute.Graphite granule can be under the effect that does not have phenyl and/or carboxyl surface functional group stable suspersion in oil.A spot of phenyl is or/and carboxyl can then be added in the graphite surface in the microfluid.In this example, graphite granule is still said does not need functional group can form stable suspension, because microfluid stable suspersion just before functional group forms.

Though in certain embodiments, microfluid does not comprise tensio-active agent, and in other embodiments; Perhaps, these microfluids comprise one or more tensio-active agents, Z 150PH polyvinyl alcohol (PVA) for example, Vinylpyrrolidone polymer poly-vinylpyrrolidone (PVP); 12 (alkane) basic sodium sulfate sodium dodecyl sulfate (SDS), succinimide succinimide, n-hexyl alcohol CATB; Methylcellulose gum, Chinese honey locust etc.

Microfluid described herein comprises one or more characteristics, and for example, perhaps microfluid has high thermal conductivity coefficient, hopes to be not restricted to any theory, and the thermal conductivity of the microfluid here is owing to the directed high thermal conductivity coefficient of graphite causes.Simultaneously, through adding micro-meter scale graphite granule rather than nanoscale particle, the obstruct of point-to-point transmission heat passage (being the lower liquid of thermal conductivity that inserts between the particle) is less, the relative nano graphite flakes of micron order graphite, and the thermal resistance that hot-fluid is run into is less relatively.

In some cases, the thermal conductivity of microfluid is at least 0.15, is at least 0.6, is at least 0.9, is at least 1.2, perhaps is at least 1.5W/mK.In certain embodiments, relative thermal conductivity is at least 1.1, is at least 1.25, is at least 1.5, is at least 1.75, is at least 2.0, is at least 2.5, perhaps is at least 3.0.Relative thermal conductivity is expressed as:

K_{R} = \frac{K}{K_{0}} - - - [1]

In the formula, K representes to comprise the thermal conductivity of the microfluid of graphite granule, K ₀The thermal conductivity that does not comprise the microfluid of graphite granule.For example, for graphite/water microfluid, relative thermal conductivity equals the thermal conductivity of the thermal conductivity of graphite divided by water.

In certain embodiments, the raising of the thermal conductivity of microfluid can reach with respect to the neat liquid that does not have graphite granule and be at least 25%, and at least 50%, at least 75%, at least 100%, at least 150% or at least 200%.Thermal conductivity strengthens and can be expressed as:

K_{enhance} = \frac{{K - K}_{0}}{K_{0}} \times 100 % - - - [2]

K and K in the formula ₀As preceding text are described.

The thermal conductivity of liquid can use the transient state hot wire process to measure, and this method is by Nagasaka and Nagashima invention [JPhys E:Scientific Instrments, Vol.14, pp.1435-1440 (1981)], here by complete reference.In order to measure the fluid thermal conductivity, a diameter is that 50 microns platinum filaments (there is 25 microns thick insulation layer on its surface) immerse in the testing liquid fully.The impulse of current of accurately knowing is through hot line, and the temperature of generation raises and measures out over time through resistance in the monitoring heated filament.The thermal conductivity of liquid is found the solution the acquisition of thermal conductivity equation through analyzing transient temperature variation profile.

Under many circumstances, with respect to the base fluid specific conductivity of no graphite granule, the specific conductivity of microfluid also can improve.For example, the specific conductivity of microfluid can improve 100 times at least, improves 500 times at least, improves 1000 times at least, improves 10000 times at least, improves 100000 times at least, improves 1000000 times at least, perhaps at least 10000000 times.In certain embodiments, the specific conductivity of this microfluid is 0.001 at least, is 0.01 at least, is 0.1 at least, is 1s/m at least, perhaps is 10s/m at least.In certain embodiments, the specific conductivity of microfluid is 100 times of base fluid specific conductivity at least, is 500 times at least, is 1000 times at least, is 10000 times at least, is 100000 times at least, is 1000000 times at least, perhaps at least 10000000 times.

Under certain conditions, described here microfluid comprise at least a kind of stable particle suspension-s.For example, in certain embodiments, graphite granule can be stablized in liquid 1 day at least, at least 1 week, at least one month, at least 6 months, perhaps at least one year.In general, a kind of steady suspension is coagulation not to take place in test period suspending phase (for example graphite granule) in essence.

Preparing method to this microfluid is illustrated on the one hand.This method comprises a large amount of graphite granules is added in the liquid, forms steady suspension.Graphite granule possesses one or more characteristics discussed above.In addition, whether suspension-s has stablizer, and perhaps stablizer is before graphite granule suspends, to add or suspend to add later on.

In certain embodiments, the process of formation microfluid optionally comprises graphite granule pre-treatment process.Graphite granule is through suitable technology manufacturing.For example, graphite granule can grind spheroidal graphite, method productions such as electroless plating through the intercalation or the natural graphite that expands.In one group of embodiment, graphite granule can be by cleavage.In this process, graphite is heated to high temperature (generally being between 600 ℃ to 900 ℃), and for example, in a stove or microwave oven, graphite can heat for 5 seconds to 180 seconds.In some situation, to add a kind of acid (for example sulfuric acid) in the graphite cleavage process.In case heating, graphite granule expands.In certain embodiments, the volume of expanded graphite can be at least 50 times of original graphite granule volume, at least 100 times, and at least 300 times, perhaps at least 500 times.Accordingly, the volume of graphite has reduced at least 50 times on the basis of original graphite, and at least 100 times, at least 300 times, perhaps at least 500 times.In certain embodiments, follow buoyancy to improve in the attenuating of graphite granule density and improved the particulate suspension.Expanded graphite can add in the fluid, and (being UW) handles to carry out sound wave subsequently.In some cases, graphite granule can be a dry state, and can disperse again in the influent stream body.

In certain embodiments, in graphite cleavage process, a small amount of functional group can remain in the surface of graphite granule.For example, after graphite granule was peeled off, particle surface possibly comprise phenyl, epoxy group(ing), carboxyl etc.Be not restricted to existing any particular theory, remaining functional group can be because chemical graft (for example sulfuric acid, or other strong acid, oxygenant etc.) or the product in stripping process.In some cases, through behind the stripping process, need not add any material (for example, do not have the functional group of graphite surface, do not have tensio-active agent, do not have stablizer) in graphite granule or the graphite microfluid basically.For example, in some cases, graphite granule is stripped from, and the particle of being stripped from then can directly add to form in the liquid stablizes the graphite microfluid, and need not add any functional group, perhaps acid, alkali, tensio-active agent, perhaps other stablizers.In certain embodiments, after graphite was passed through stripping process, graphite granule can directly form steady suspension, need not add any material (comprising acid, alkali, tensio-active agent, functional group etc.).For example in many situation, after graphite is stripped from, a kind of acid; A kind of functional group; Perhaps/possibly be added in the graphite and (also comprise the s.t. process) with other stablizers, but graphite granule still can form steady suspension, even without acid or other stablizers.In many situation, acid, the adding of alkali or other materials does not have the material influence to the stability of graphite granule suspension-s.

As stated, system and method described herein can be used to prepare thermal conductivity and/or electroconductibility enhance fluid, and relevant similar non-graphite microfluid.This type fluid can find some special purposes, for example, and in heat exchange system.Effectively heat transfer helps effectively cooling off with less relatively interchanger.In addition, this microfluid also can be used as the conductivity fluid.

System and method described herein relatively has lot of advantages with traditional thermal conductivity.For example, the fluid that comprises nano particle or nanotube is easy to reunite or twines and cause two to be separated.And micron graphite particle described herein relatively easily suspends, because the little (2-2.2g/cm of density ³) and surface-area big perhaps/and bigger surface charge density.And graphite granule has thermal conductivity in the bigger face (about 1000W/Mk or more).And relative carbon nanotube and other nano materials, the micron graphite particle is relatively cheap.Graphite also is a kind of natural lubricant, can reduce the surface disturbance (the for example figure layer of workpiece surface) of the device that contacts with fluid.At last, the large-size of micron graphite (with respect to nano particle) help the transmission in the graphite flake of high heat conduction of hot-fluid physical efficiency long period and reduce hot-fluid low thermal conductance granular boundary between the chance of fluid transmission

The present invention relates to control suspension-s thermal conductance and electric article of leading, system and method is also done general description at this.In certain embodiments, some comprise that particulate suspension-s has variable thermal conductance and/or electricity lead (for example, particle can improve thermal conductance with or electricity lead).Here the thermal conductivity of suspension-s and/or electroconductibility can change through the phase transformation of suspension-s (for example, solidify or melt).For example, thermal conductivity and/or electroconductibility can improve through solidifying of suspension-s.In certain embodiments, comprise in the fluid process of setting of suspended particle forming polycrystalline, comprise crystal boundary and crystal grain.In case after fluid solidified, the particle in the fluid can be moved to crystal boundary and got on and cause particulate density on the crystal boundary obviously greater than crystal grain inside particulate density.The particle of high density has just formed particle network on the crystal boundary, is described below.

In some cases, thermal gradient and/or potential gradient can be set up in the suspension-s system.In these cases, this suspension-s is in first phase (solid) and has the high relatively capacity of heat transmission and conductive capability than being in second phase (liquid).These embodiment perhaps have some purposes aspect the thermistor making and control, for example, and restrictor, TP, overcurrent self-protecting device, automatic control heating unit etc.

According to one group of embodiment, Fig. 7 A-7C has set forth the synoptic diagram of suspension-s phase transition process.Among Fig. 7 A, particle 110 is suspended in the fluid 112, forms stable suspension.Shown in Fig. 7 A, these particles all have been distributed in the medium basically.In other embodiment, when the suspension media was liquid, these particles may form a large amount of groups bunch in fluid.In certain embodiments, when suspension-s under liquid state, these particles may form chain-like structure (for example, owing to solidify with thaw cycle cause) in fluid.

In certain embodiments.One-level or multi-level phase change (for example, solidify and melt) can take place in the medium in these suspension-s, these compare thermal conductance that process can change suspension-s perhaps/lead with electricity.For example in some cases, a kind of suspension-s of liquid state (suspension-s that comprises liquid medium) can solidify and form mixture (suspension-s that comprises particle and solid dielectric).The suspended substance here should be appreciated that it promptly is that liquid suspension-s also can be solid-state matrix material.Fig. 7 B is a synoptic diagram after Fig. 7 A suspension-s solidifies.In case freezing, fluid 112 forms polycrystalline solid suspension medium, comprises 116 crystal grain and 118 crystal interfacies, so form solid composite.In refrigerating process, these particles can be moved to crystal boundary, make the granule density at crystal boundary place significantly greater than intragranular particulate concentration.These particles have formed particulate network (being exactly an interconnective network of particle) to the migration of crystal boundary.Fig. 7 B has provided the synoptic diagram that particle 110 is moved to polycrystalline crystal boundary 118 and formed network.

In some cases, this solid state composite (suspension-s that promptly solidifies) is liquid suspension relatively, has very big thermal conductivity and perveance.In certain embodiments, the thermal conductivity of this suspended solid is at least 2 times of liquid thermal conductivity factor, at least 3 times, and perhaps between 2 times at least 5 times.In some instances, the electroconductibility of solids suspension is at least 2 times of liquid suspension at least, at least 5 times, and at least 10 times; At least 50 times, at least 100 times, at least 1000 times, or between 2 times-1000 times; Between 2 times-100 times, between 5 times-1000 times, between 10 times-1000 times.Do not receive the restriction of other any particular theory; This solid-state matrix material have relatively large heat conduction perhaps/with electroconductibility be (and internal stress) because particle gathering on crystal boundary, the formation that has caused heat conduction or conductive network of gathering of this particle high density makes heat and/or electric energy effectively transmit.The thermal conductivity of fluid or suspension-s can be through being measured by the thermal transient collimation method of Nagasaka and Nagashima invention [J Phys E:Scientific Instrments, Vol.14, pp.1435-1440 (1981)].

In certain embodiments, solid composite material can melt the formation liquid suspension.Fig. 7 C comprises that solids suspension melts the synoptic diagram that the back forms liquid suspension again among Fig. 7 B.In Fig. 7 C, particle 110 is dispersed in (being liquid 112) in the liquid medium.Shown in Fig. 7 C, these particles are homodisperse.But in certain embodiments, it is network-like that these particles still keep, and melts the back at suspension medium at least and keeping these networks to a certain degree.In some cases, these particles focus in a large number and form group bunch, and in other cases, after suspended substance melted, particle still kept some network structures.

With respect to solid composite material, melt and to reduce its suspension-s thermal conductivity and/or electroconductibility.In certain embodiments, the thermal conductivity ratio solids suspension of the liquid suspension after the thawing is to when young 2 times, to when young 3 times, to when young 5 times, between 2-10 times, perhaps between 2-5 times.Under certain conditions, the liquid suspension after the thawing electroconductibility than solids suspension to when young 2 times, to when young 5 times, to when young 10 times; To when young 50 times, to when young 100 times, to when young 1000 times, between 2-1000 times; Between 2-100 times, between 5-1000 times, between 10-1000 times; Be not restricted to any particular theory, thermal conductance or the reduction led of electricity are because solid melts, and particle is distributed in the medium institute extremely again.

The heat conduction and/or the electroconductibility of liquid suspension wanted high before under certain conditions, the later liquid suspension liquor ratio after melting was again solidified.For example, the first liquid phase suspension-s that has first specific conductivity and first thermal conductivity in some cases solidifies and forms solid-state matrix material.Subsequently, this solid state composite can melt and form second liquid suspension, and this second flowing fluid ratio, first liquid suspension has higher thermal conductivity and/or electroconductibility.Be not subject to existing any theory, the thermal conductivity of second liquid suspension (suspension-s that promptly melts again) and/or electroconductibility are because still have some particulate coacervates (promptly having formed the particulate network) in second liquid suspension of solids suspension after dissolving than the first liquid suspension height.In some cases, the heat conduction of these second liquid suspensions and/or electroconductibility is than at least 2 times of the first liquid suspension height, at least 5 times, or 2-10 doubly between.

Suspension medium described herein can experience phase transformation many times (promptly solidifying/thaw cycle).In certain embodiments, suspension-s is tending towards constant in the variation through (after promptly circulation removes for the first time) heat conduction of the phase transformation of repeatedly solidifying and melting circulation back and electroconductibility.For example under certain conditions, the variation of heat conduction and electroconductibility is at least 20% in the solid-liquid two phase phase transformations, is at least 10%; Be at least 5%, be at least 1%, perhaps keep identical multiple to change basically at least at 2; At least at 5; At least at 100, at least at 1000, perhaps more solidify thaw cycle after.Should be realized that one solidifies/and thaw cycle comprises that suspension-s becomes solid-state and from solid-state transformation to liquid from liquid state.

Particle described herein can be made up of a lot of suitable materials.For example under certain conditions, particle can be made up of metal, can be pure metal or alloy.Under certain conditions, metal can be a nanoscale particle.This metallic particles comprises, metal nano-tube for example, metal nanometer line, metal nano dish, nano metal sheet, perhaps nano metal fiber.In certain embodiments, because the high heat conduction and the high conductive characteristic of particle itself, so the use of metallic particles has some advantages.In certain embodiments, particle can comprise some MOXs.

In certain embodiments, particle comprises the crystalline material that shows base plane cleavage characteristic.Basal cleavage is a kind of common phenomenon, is meant that material is along being parallel to the dissociated characteristic of crystal base plane direction.These materials include, but are not limited to following material, blotite for example, white mica, phlogopite, lithionite; Margarite, glaukonine etc.), clay mineral matter (kaolinite for example, illite, polynite, smectite; Vermiculite, talcum, magnalium skin stone, pyrophyllite, etc.) and other materials.

In certain embodiments, the carbon back particle is used.Under certain conditions, the carbon back particle comprises the aromatic condensed ring network, and particle is made up of basic carbon atom.A kind of aromatic condensed ring comprises at least 10, at least 50, at least 100, at least 1000, and perhaps at least 10000 aromatic nucleus.In certain embodiments, the carbon back particle comprises higher relatively carbon content (perhaps 99.9wt% at least, wt is a mass parts for 95wt% at least for example, 99wt% at least), and carbon content is calculated and do not comprised any other functional groups that are connected on the particle.Carbon back particle condensed ring end possibly comprise some borders arbitrarily.For example, a slice Graphene comprises a plane one of carbon tip, and the carbon nanometer comprises the terminal nanostructure of an on-plane surface.Under certain conditions, these end structures are replaced by Wasserstoffatoms.In some cases, these end structures are comprised that the group of Sauerstoffatom replaces (for example phenyl).Carbon back particulate instance includes, but are not limited to graphene film, graphite granule, carbon nanotube, carbon nano wire, carbon nanometer plate, carbon nanobelts, carbon nanofiber.In certain embodiments, the carbon back particle has lot of advantages owing to self higher heat conduction and conductive capability.

In certain embodiments, the particle in suspension-s can be graphite granule, and is as shown in Figure 1.Graphite granule can be formed by the graphite of a lot of forms.In certain embodiments, graphite granule can comprise or processed by natural graphite.According to one group of embodiment, Fig. 2 has provided the optics picture of a typical graphite granule.Any type of graphite (comprises natural graphite, synthetic graphite.Peel off graphite etc.) can be as the particle of the suspension-s of mentioning in this patent.

Use graphite to be beneficial to preparation LV suspension-s especially.Mention as indicated that graphite also can be used as super lubricant.The super lubricated frictional force between two surfaces that is meant, near but non-vanishing phenomenon.The use of super lubricant (for example graphite) can keep lower frictional force in suspension-s.And the low-frictional force fluid allows less relatively pump horsepower effectively to circulate, and reduces the effective damage to moving parts in the equipment.The high thermal conductance fluid of low in addition friction has dual function concerning the application that needs effectively lubricating and efficient heat transfer.Not with other conflict of theories, this super graphite lubrication effect is owing to less action force between graphene layer (being Van der Waals force) causes.

In certain embodiments, this grain diameter has (perhaps a less than) micro-meter scale at least.The selection of grain diameter is most important to forming steady suspension.For example, the particle of micro-meter scale with respect to millimeter or more the particle of big scale suspend easily.And the possibility that the suspension-s that comprises micrometer size granule stops up heat pipes is millimeter or more large-size particle suspension-s is little relatively.

In some cases, most of particulate cross-sectional dimension are less than 10 microns.Of preamble, the maximum cross section is meant that some graphite flakes can measure the ultimate range on two borders.So average maximum cross section is meant graphite flake and can measures several MVs of two ends ultimate range.The method of a general test maximum cross section size is to analyze the SEM photograph.In certain embodiments, most particulate cross-sectional dimension are less than 1 micron, less than 100 nanometers, or between 1 nanometer-10 micron, between 10 nanometers-10 micron, perhaps between 1 nanometer-1 micron, perhaps between the 1-100 nanometer.

In some cases, most of particulate yardsticks are micron order in the suspension-s.For example, in certain embodiments, at least 80%, at least 90%; At least 95%, perhaps to have the maximum cross section be 10 microns at least 99% particle at least, 1 micron; At least 100 nanometers are perhaps between 1 nanometer-10 micron, between 10 nanometers-10 micron; Between 1 nanometer-1 micron, between 10 nanometers-1 micron, perhaps between 1 nanometer-100 nanometer.

In certain embodiments, these particles have bigger flakiness ratio.For example, these particles are made up of some thin slices.In general, the thickness of thin slice is far smaller than lateral length.In certain embodiments, these particles comprise elongated structure, micron tube for example, micro wire, micrometer fibers, micron awl, nanotube, nano wire, nanofiber, nanocone and similar structures.These thickness of structure are basically all less than the size of length direction.In certain embodiments, great majority 80%, at least 90%; At least 95%, perhaps two quadrature length ratios of particle of at least 99% were at least 3: 1, were at least 5: 1; Be at least 10: 1, be at least 50: 1, be at least 100: 1; Be at least 500: 1, be at least 1000: 1, perhaps be at least 10000: 1.

In certain embodiments, these particles have big thermal conductivity at least in one direction.In some cases, in a direction, thermal conductivity is at least 10W/mK to these particles, is at least 50W/mK, is at least 100W/mK at least, and 500W/mK is at least 1000W/mK, is at least 5000W/mK, and probe temperature is 25 degree.In certain embodiments, at 25 degree, these particulate thermal conductivitys (at least one direction) are at least 5 times of base fluid thermal conductivity in the suspension-s; At least 10 times, at least 100 times, at least 1000 times; At least 10000 times, at least 20000 times, perhaps 5-20000 doubly; 10-20000 times, 100-20000 times, perhaps 1000-20000 doubly.

In certain embodiments, these particles have higher relatively electric conductivity in a direction.In some situation, for example the electric conductivity of these particulate materials (at least in a direction) is at least 100S/m, and 1000S/m, 10000S/m, 100000S/m, 1000000S/m, probe temperature are 25 degree.In some cases, the electric conductivity of these particulate materials (at least one direction) is 5 times of base fluid electric conductivity, 10 times, and 1000 times, 10 ⁶, 10 ¹², 10 ¹⁶, 10～10 ¹⁶Doubly, 10 ⁶～10 ¹⁶Doubly, probe temperature is 25 degree.

In some cases, particle described herein is led efficiency far greater than second direction (being the direction of vertical first direction) at the thermal conductance and/or the electricity of first direction (and/or more multi-direction, for example direction in the face in the lamellar structure).Here it is anisotropic conductor.Thermal conductance and/or electricity are led more effective first direction, are meant the direction (being parallel and Graphene planar direction) along the particle length direction.The thermal conductance of second direction and/or conductance ratio first direction are low, refer to particulate thickness direction (the for example direction of graphene film multilayer intersection).In certain embodiments, be longer than second direction like the fruit granule first direction, this particle is exactly a highly heat-conductive material in the face.This anisotropic conductive material comprises, graphene film, graphite granule, carbon nanotube, carbon nano wire and analogous material.

In some cases, these particles have low relatively specific conductivity, but high relatively thermal conductivity.For example, these particles comprise silit (for example, nanometer silicon carbide particle, SiC nano fiber).In certain embodiments, these particles can comprise SP 1.In some cases, these particles can comprise some polymkeric substance (for example polymer fiber).For example, these particles comprise electrical isolation, but relative high thermal conductivity high polymer material.

Any suitable fluid (for example, liquid, colloid) may be used to the base fluid of suspension-s.In some cases, suspension medium comprises hydrogel.Hydrogel is a kind of material that comprises polymer network, and these networks can limit and comprise water in its structure.This hydrogel comprises the cross-linked polymer chain, and is no matter directly crosslinked or crosslinked through linking agent.In some cases, this degree of crosslinking be can change, and its receptivity and the ability that keeps water changed.The polymer that can form hydrogel comprises and contains polymeric silicon that polyacrylic ester, cross-linked polymer are (for example; Polyethylene oxide, polymeric amide and Vilaterm are than pyrrolidone (PVP), Z 150PH; Acrylate polymeric (for example, ZX-I) and hydrophobic multipolymer

In certain embodiments, suspension medium is solid (for example, a polycrystalline solid).This suspension medium can obtain through frozen liq.If the polycrystalline solid is an expected results, can forms polycrystalline liquid and obtain through solidifying.A kind of identification liquid commonly used solidifies whether form polycrystalline solid method, can be used to screen fluid, and for example, freezing a kind of fluid carries out suitable crystal structure analysis then.Whether forming the polycrystalline method after a kind of identification fluid commonly used solidifies is X-ray diffraction method (XRD).

Suspension medium comprises the suitable composition of any form (not considering its phase).For example, the medium of this suspension-s comprises organic or inorganic components.These compositions are including, but not limited to, water, alcohol (for example, terepthaloyl moietie, ethanol), the combination of hydrocarbon polymer (for example, n-Hexadecane, eicosane, tridecane, dodecyl, undecane, ten alkane, octadecane, pentadecane) or these materials.Under certain conditions, the medium of these suspension-s comprises water seeking liquid (for example, water, alcohol etc.).In general, hydrophobic nature and wetting ability be meant a kind of fluid whether can not have under tensio-active agent or other function of stabilizer miscible and form the characteristic of stabilized mixture with water.In certain embodiments, the HMP material is also contained in the suspension medium relatively.For example, in some cases, suspension medium can comprise a kind of metal.For example, liquid can comprise scolder, like tin, and copper, silver, bismuth, indium, zinc, antimony, the mixture of lead and/or these metals.In some cases, also possibly use other fluids.Use which kind of fluid to depend on the purposes of this suspension-s.

In certain embodiments, the selection of the composition in this suspension medium at least partly is to depend on the zero pour of this composition and/or molten point (the zero pour here is different with molten some temperature).For example, the selection of the composition of this suspension medium is because its zero pour and/or dissolve point some distinct temperature scope (for example-120 ℃～200 ℃ between).Under certain conditions, the selection of this certain composition of suspension medium is because its zero pour and/or molten point are perhaps low slightly near envrionment temperature.This suspension-s can be applied in some to the high temperature apparatus sensitive.Under certain conditions, the selection of the composition of this suspension medium is owing to its zero pour and/or dissolves point between-120 ℃～40 ℃, between-20 ℃～40 ℃ degree, between-5 ℃～40 ℃, between 0 ℃～35 ℃, between 15 ℃～25 ℃ etc.This through selecting different zero pour and the method for dissolving the some medium can change phase transformation (therefore change thermal conductance and electricity the is led ability) temperature of suspension-s, and be applied in some special place.For example, near temperature detection sensor water can be used for 0 ℃.The another one example, n-Hexadecane, zero pour/molten point is 18 ℃, can be used to detect near the transmitter room temperature.

Here said suspension-s comprises the particle of all suitable concns.In certain embodiments, the particle concentration volume(tric)fraction that comprises in the suspension-s is lower than 2%, perhaps is lower than 1%; Perhaps at 0.01%-2%; Perhaps between 0.05-2%, perhaps between 0.1-2%, perhaps between 0.5-1%; Perhaps between 0.6-0.9%, perhaps between 0.7-0.85%.In certain embodiments, also can the suspension-s of compound particle concentration outside above-mentioned category.A technology commonly used is the volume(tric)fraction of nano particle in calculating suspension-s in the industry.For example, when metering, at first need weighing particulate quality.The particulate volume then can come out divided by the particulate density calculation through the quality of weighing.Then, the volume(tric)fraction of nano particle can be calculated through the volume (the volume sum of particle and liquid medium) of particulate volume divided by suspension-s.

In certain embodiments, can in suspension-s or its solid-phase construction, apply voltage.For example,, possibly play a role during at it when suspension-s as thermistor a part of.In certain embodiments, suspension-s maybe be as TP.In certain embodiments, when electromotive force was applied to the liquid suspension two ends, its specific conductivity was lower.When being exposed under the low relatively temperature, suspension-s solidifies, and the solid phase matrix material of formation will have higher specific conductivity.Higher specific conductivity will allow electric current through suspension-s under the solid phase, for example can be used for the driving of atmosphere control system.The common skill that Certainly in the industry is to constitute TP by this solid phase matrix material, can melt when it is exposed under the sufficiently high temperature, cuts off electric current thereupon.As the another one example, this suspension-s can be used as current fuse.In certain embodiments, applying electrical potential can be clipped in the higher solid phase matrix material two ends of specific conductivity, makes electric current from matrix material, pass through.After electric current surpassed threshold value, the solid phase matrix material can be owing to resistance heating (being joule heating) melts.Melt back solid phase matrix material and will become the liquid phase suspension-s that has than low conductivity.The electric current that relatively low specific conductivity will cause wherein passing through in the suspension-s significantly descends (perhaps ending), plays the effect of fusible cut-out thus.

In some cases, the gradient of heat maybe be by on suspension-s (liquid suspension for example, solid-state matrix material, or have both at the same time).For example, thermal gradient possibly be applied on the solid-state matrix material with higher heat-conductivity, causes heat to cross solid composite material.If the temperature of solid composite material exceeds critical level, it will melt, and cause forming the liquid suspension that has than lower thermal conductivity.The relative low-heat conductance of liquid suspension may cause the reduction through the heat transfer amount of suspension-s, and for example this, possibly protect the temperature sensor in suspension-s downstream.

Suspension-s described herein can be used for controlling the transmission of heat or electricity in certain embodiments in a plurality of positions.For example, liquid in some cases suspension-s can be transported to first position and freezing, to improve electricity and/or heat flowing in first position.In some cases, solid composite material can be melted again, is transported to second position, and freezing again electricity and/or hot flowing to improve second position place.Can constantly implement this additional transmitting step to improve electricity and/or heat in the 3rd, the 4th, the 5th perhaps electricity and/or the heat flow of any additional position.Transmission between the different positions can be passed through, and for example, the gradient of on suspension-s, exerting pressure realizes (for example, use vacuum, pump, or any suitable device).

Suspension-s described herein can obtain through any suitable method.In certain embodiments, suspension-s can be through getting up to obtain (for example, through in liquid, adding particle or in particle, adding liquid) with multiple particle and liquid combination.

In some cases, particle described herein can functionalizedly make it comprise surface functional group.The functionalized stability that can enhanced granule suspension-s of particulate.For example, hydrophobic relatively particle can become hydrophilic relatively through functionalized its surface that makes, and can in water seeking liquid such as water and alcohol, form steady suspension.In addition, hydrophilic relatively particle can be through functionalized its surface relative hydrophobic that becomes that makes.The particulate surface can be functionalized by a large amount of different functional groups, for example comprises hydroxyl, carbonyl, epoxy group(ing) or the like.

In some cases, particle can form steady suspension in liquid under the situation that lacks surface functional group.In some instance, particle can form steady suspension in liquid under the situation that lacks tensio-active agent.In some cases, particle can form steady suspension in liquid under the situation that lacks stablizer.As pointed at elswhere, stablizer refers to respect at (that is: temperature, pressure etc.) under the identical condition but lack for the particle under the situation of stablizer any entity that can increase stability of suspension.The instance of stablizer comprises: for example, dispersion agent, acidity, basic material are adsorbed on the stable functional group (being phenyl, carboxyl) of particle surface and materials similar.

Suspension-s described herein possibly be to be made up of stable particle suspension liquid in some cases.For example, in some instance, particle can stably be suspended in the liquid suspension medium at least one day, at least one week, January at least, June at least, perhaps at least one year.Generally speaking, a steady suspension is a kind of suspension-s that in the time cycle of its use, does not have substantive solids precipitation to take place.The system and method that forms this stable graphite suspension for example has similar description in the number of patent application of on December 15th, 2009 application is 12/638,135 USP " graphite microfluid " in other patents, this patent at this by whole reference.

System and method described herein and traditional thermistor and other temperature and/or current control system are compared, and perhaps one or more meliority will be provided.For example, and similarly compare, make relatively fast and cheap based on the device of suspension-s based on the device of electronics.In addition, this system based on suspension-s can near execution work room temperature, and can just can change the execution temperature of device through the composition of changing suspension medium simply.The system of the suspension-s base in temperature or current control system also can simply be transported to another position through the pump or other the fluid hierarchy of control from a position.

Following Example attempts to illustrate the specific embodiment of this invention, but can not be interpreted as limitation, can not simplify whole categories of this invention.

Embodiment 1

In this example, the production and the test of graphite microfluid have been described.Natural graphite come from Asbury Carbons company (Asbury Graphite Mills, Inc., NJ, USA).The chemical oxidation process that people such as use Tryba propose (Carbon 43 (2005), pp.2397-2429, from all considerations, the document is done as a whole by index) natural graphite is used for producing graphite intercalation compound.Different volumes fractional hydrogen peroxide (from 0 to 30%) and sulfuric acid H ₂SO ₄Mix, prepare the oxygenant of intercalation technology.2.2 the natural graphite of gram and 100 milliliters oxygenant at room temperature reacted 30 minutes.The slurry that has reacted rinsing in deionized water reaches 6 to 7 to pH, is placed on then on the hot platform 80 ℃ of bakings 24 hours.Then graphite heated 5 seconds to 180 seconds in Haier's microwave oven of 1100W, and with original size compared, the volume of graphite will expand above 300 times.Graphite after then expanding is added into the graphite granule that ultra-sonic dispersion suspended with generation in 15 to 120 minutes in the solvent.

The influence of graphite granule concentration to thermal conductivity measured in beginning.Polyalpha olefin synthetic base oil (" PAO "), terepthaloyl moietie and water are used as the liquid phase part of microfluid.Volume(tric)fraction is respectively 0.1%, 0.3%, and 0.5%, 0.6%, 0.7%, 0.8%, 0.9% and 1.0% graphite granule is added in three kinds of solution, forms 24 kinds of graphite microfluid samples.Use the transient state hot wire process of Nagasaka and Nagashima invention to measure for the thermal conductivity of every kind of graphite microfluid sample.In this example, the platinum filament that diameter that has applied 25 micron thick insulation layers is 50 microns is immersed in the sample fully.Through the accurate pulsed current of dose known amounts, the function that the temperature that is caused rising is used as the time detects through changes in resistance in the monitoring platinum filament in the platinum filament.Through adopting separating of heat conduction equation to analyze the profile that transient temperature changes, the thermal conductivity of each sample just can be decided.

Fig. 5 A-5B has comprised the thermal conductivity figure and the thermal conductivity enhancing figure of the microfluid sample with different graphite particle volume(tric)fraction respectively.When graphite granule concentration is 1% volume(tric)fraction, all show in all three fluids and surpass 100% thermal conductivity increase.Shown in Fig. 5 B; The graphite granule that adds 1% volume(tric)fraction will improve its thermal conductivity in the water and surpass 1.27W/mK, and that the increase of thermal conductivity reaches is high 110% (during corresponding to 25 ℃ deionized water thermal conductivity (0.6W/mK) surpass 2.1 times relatively hot conductance).In addition, Fig. 5 A-5B has explained that thermal conductivity presents nonlinearities change along with the variation of graphite granule volume(tric)fraction, and when higher graphite granule volume(tric)fraction, thermal conductivity improves increasing.

Then, the specific conductivity of ethylene glycol microfluid is measured.Volume(tric)fraction is respectively 0.01%, 0.02%, and 0.03%, 0.05%, 0.07%, 0.85%, 0.1%, 0.2% and 0.3% graphite granule is added in the terepthaloyl moietie.The specific conductivity of pure glycol sample is also measured in addition.Fig. 6 has comprised the specific conductivity (on logarithmic axis) of 9 specimen.The specific conductivity of microfluid never comprises 7 * 105 of graphite granule and is increased to the 0.6s/m that surpasses that comprises 0.2% volume(tric)fraction graphite granule microfluid, has increased by four one magnitude.

Embodiment 2

This example has been described through the electricity of phase transformation controlled material and thermal property.Use graphite-n-Hexadecane suspension-s, conductivity of electrolyte materials can change two one magnitude at 18 degrees centigrade, and thermal conductivity can change three times.

The suspension-s that is in this example comprises the cleavage graphite flake layer that is suspended in the n-n-Hexadecane (99.5+%, Sigma Aldrich produces).At first, the graphite flake layer of cleavage by natural graphite (Asbury Graphite Mills, Inc., NJ, USA) through the preparation of chemical graft and dilatometry, (Carbon 43 (2005), pp.2397-2429 like the technology of people such as Tryba proposition.The oxygenant of intercalation process using comprises 85 milliliters sulfuric acid (96%, Alfa Aesar produces) and 15 milliliters hydrogen peroxide (30%, Alfa Aesar produces).In intercalation technology, the natural graphite of 2.2 grams and 100 milliliters oxygenant at room temperature reacted 60 minutes.Subsequently, remaining salt and acid are removed in the slurry that has reacted rinsing in deionized water.With the slurry by filtration after the rinsing and be placed on the hot platform 110 ℃ of bakings 24 hours to obtain graphite intercalation compound.Expanded graphite is to obtain in 30 seconds through the graphite intercalation compound for preparing is added thermal expansion in the microwave oven of 1100W.It is 1% graphite suspension that graphite after the expansion then is dispersed in the n-n-Hexadecane solvent to obtain volume(tric)fraction.In order to obtain graphite flake layer, the expanded graphite in the suspension-s passed through the ultrasonic cleavage of high-energy ultrasonic probe (750,750 watts of Sonics Vc, the output of 80% power) 15 minutes.Obtain homodisperse product.Volume(tric)fraction is respectively 0.2%, 0.4%, and 0.6%, 0.8% suspension-s is through further interpolation n-n-Hexadecane and continue acquisition in ultrasonic 3 minutes.By the time the sample cool to room temperature has just obtained steady suspension.

XPS analysis shows that the surface of graphite flake layer contains 8% Sauerstoffatom, is not restricted to any theory, these Sauerstoffatoms perhaps come from graphite surface hydroxyl, epoxy group(ing) and carboxyl.

The form of expansion back and cleavage graphite flake layer is observed through ESEM (SEM) (EOL JSM-6320).The microstructure of cleavage graphite is at room temperature observed through transmission electron microscope (TEM) (JEOL 200cx, JEOL 2011).The mean diameter of graphite flake is several microns, and thickness is a few to tens of nanometers.Fig. 8 A has comprised typical in above-mentioned sulfuric acid intercalation, the graphite flake SEM image of microwave expansion and ultrasonic cleavage process.Most of graphite flakes are uneven, and some of them have formed web-like (Fig. 8 B).This possibly be because the internal stress of bringing out in the preparation process causes.Fig. 8 C is the high resolution scanning Electronic Speculum figure in zone " a " among the figure B.Can find that this graphite flake comprises about 30 layers of atom, about 0.335 nanometer of average layer spacing is with observed data consistent in the graphite.Fig. 8 D is that volume(tric)fraction is the light micrograph of graphite/n-Hexadecane suspension-s of 0.2%.From this photo, can observe graphite flake and form three-dimensional and exceed and ooze network.Ambiguous zone is owing to non-coplanar graphite flake layer overfocus or owe Jiao and cause in the light micrograph.Exceed the formation of oozing network and show the formation of dense thick graphite/n-Hexadecane suspension-s.Fig. 8 E is that graphite/n-Hexadecane suspension-s of 50 milliliter 0.2% is preparing the trimestral photo in back.Can find out that suspension-s is highly stable, in suspension-s, not see deposition in fact.

The resistance of suspension-s is through pouring suspension-s in the homemade conductive box, and these box two ends vertically are inserted with area 1.17cm2, the copper electrode that spacing is 4.85 centimetres.The system resistance of this conductive box is approximately 0.8 ohm.The electricity of graphite suspension is led by computes:

A mistake! Do not find Reference source.[1]

Wherein R is the resistance of measuring, and K=3.83cm-1 is the conductive box constant.

The thermal conductance measurement of graphite suspension is to use the transient state hot wire process of Nagasaka and Nagashima (J.Phys.E:Sci.Instrum.14,1435 (1981)) development to measure.The platinum filament that diameter that has applied 25 micron thick insulation layers is 50 microns is immersed in the sample fully.Through the accurate pulsed current of dose known amounts, the function that the temperature that is caused rising is used as the time detects through changes in resistance in the monitoring platinum filament in the platinum filament.Through adopting separating of heat conduction equation to analyze the profile that transient temperature changes, the thermal conductivity of each sample just can be decided.

The specific conductivity of graphite suspension and thermal conductivity change noticeably at 18 ℃.Fig. 9 A is the specific conductivity and the temperature relation figure of graphite suspension.Under liquid state, the specific conductivity of graphite suspension is along with variation of temperature is almost constant.When temperature was between 17.5 ℃ and 18.5 ℃, specific conductivity increased about two one magnitude.After n-Hexadecane freezed, specific conductivity settled out again.In solid-state and liquid state, specific conductivity all increases along with the increase of content of graphite.Yet shown in Fig. 9 B, the specific conductivity of the suspension-s after freezing reached 250 times peak value with the ratio of the specific conductivity of liquid suspension (increase of the clear freezing specific conductivity that causes of this numerical tabular) at about 0.8% o'clock in the volume(tric)fraction of graphite.

Shown in Fig. 9 C, the thermal conductivity of graphite suspension is also along with freezing and rise.When volume(tric)fraction 0.8%, the thermal conductivity of suspension-s has increased by 3.2 times (Fig. 9 D) through freezing.

In order to obtain graphite/n-Hexadecane suspension-s clear image that microstructure develops in freezing and ablation procedure, we have used the suspension-s sample (0.05% graphite/n-Hexadecane) of a dilution.Under liquid state, graphite flake is evenly dispersed in the n-Hexadecane relatively.In some cases, a part of graphite flake adsorbs each other, forms graphite grain bunch.In Fig. 9 E, the zone of black is corresponding to graphite grain bunch, and the n-Hexadecane crystal demonstrates acicular structure.In the refrigerated process, graphite flake is shifted onto the crystal boundary place by the n-Hexadecane needle-like crystal of anisotropic growth, generates a kind of three-dimensional and exceedes and ooze network (Fig. 9 F).When the refrigerated n-Hexadecane melts again, remove graphite and exceed and ooze network and still exist, some graphite flakes that freely suspend also can be observed (Fig. 9 G).

The electricity of graphite suspension is relevant with the evolution of its microstructure with the variation of heat.When first time refrigerated the time, most of graphite flakes have been pulled to the crystal boundary place, have formed exceeding of tight contact to ooze network, have increased the contact area of graphite flake, have reduced the contact resistance of heat with electricity.When the refrigerated n-Hexadecane melted again, the contact area between the graphite flake reduced rapidly.Yet many graphite flakes are limited in exceeding and ooze in the network, have only less relatively graphite flake to be suspended in the liquid of thawing.With respect to primary suspension-s, the specific conductivity of the suspension-s that heavily melts doubles.After first circulation, exceed and ooze structure and become more stable, specific conductivity and thermal conductivity are tending towards constant at ratio freezing and that heavily melt under the situation.

It is relevant with the density of graphite grain bunch that the specific conductivity of graphite suspension and the velocity of variation of thermal conductivity show.When graphite flake is transported to the crystal boundary place, n-Hexadecane crystalline growth the group bunch formation.When the graphite volume(tric)fraction was low, many groups bunch were isolated.Along with the increase of graphite volume(tric)fraction, increasing graphite grain bunch couples together, direct liquid and solid-state between the ratio of conductivity (comprising electricity and heat), shown in Fig. 9 B and 9D.When the graphite volume(tric)fraction further increases, graphite grain bunch has just formed good connection under liquid state.When denseer graphite suspension is frozen, the variation of specific conductivity and thermal conductivity will diminish.Moreover the grain-size of n-Hexadecane will reduce along with the increase of content of graphite, and this pressure that n-Hexadecane crystalline anisotropy growth will be caused reduces.The result makes the maximum of liquid and solid-state specific conductivity down and thermal conductivity change and when graphite volume(tric)fraction 0.8%, is observed.

Figure 10 has showed a room temperature experimental installation, is used for measuring the contact resistance of two graphite flake layers that strip down under the n-Hexadecane environment.Vilaterm vessel that comprise liquid n-Hexadecane are as container.Two graphite flake layers are immersed in the n-Hexadecane, and each graphite flake links to each other with volt ohm-milliammeter through the gold thread of 30 microns of diameters.Graphite flake is from high pyrolytic graphite (HOPG SPI-1, SPI Supplies company), to strip down.The size of graphite flake approximately is 3 centimetres of 1 micron * 3 cm x.Graphite flake contacts through the position of adjustment gold thread.The temperature of this device and resistance are measured through volt ohm-milliammeter.The internal stress of n-Hexadecane is measured (Pressures, Sensor Products company) through the ultralow pressure characterization of membrane, and data are analyzed through Topaq software (Sensor Products company).The high pyrolytic graphite of peeling off is crooked uneven.When they were close to each other, contact area was very little, made that thus the resistance between the graphite flake is very high.There is intensive anisotropic growth kinetics in n-Hexadecane, and gap is above 10 times between the different crystal orientation.In the n-Hexadecane refrigerating process, can form needle-like crystal, its slenderness ratio depends on chilling rate.Do not hope to be limited to any particular theory, n-Hexadecane crystalline anisotropic growth possibly show generation pressure at graphite flake, has increased their contact area fast.After freezing, contact area and resistance tend towards stability.After n-Hexadecane heavily melts, the pressure that graphite flake shows be released and contact area because the repulsion between elastic recovery and the particle descends fast (Figure 11 A).When temperature drops to 17.5 ℃ from 18.5 ℃, the resistance of electric current descends 460 times, shown in Figure 11 B.Figure 11 C is the stress pattern in the refrigerated n-Hexadecane.Pressure is non-uniform Distribution between 74Psi and 400Psi.Mean pressure in the refrigerated n-Hexadecane is approximately 160Psi.Do not hope that perhaps pressure distribution heterogeneous causes owing to n-Hexadecane crystalline anisotropic growth by any particular theory constraint.The bending stiffness of graphite flake only has 9 * 10 ^-11Square nanometers, cause under the 160Psi mean pressure between the graphite flake changes in resistance above 400 times.

Claims

1. microfluid comprises:

A kind of hydrophobic fluid and a large amount of graphite granules, the average largest cross-sectional sized of graphite granule are between 500 nanometers and 10 microns, and wherein graphite granule lacks on its surface under the situation of functional group and in fluid, forms steady suspension.

2. the microfluid in the claim 1, wherein fluid comprises oil.

3. the microfluid in the claim 1, wherein graphite granule is not included in its surperficial functional group.

4. the microfluid in the claim 1, wherein graphite granule can form steady suspension in fluid under the situation that lacks dispersion agent.

5. the microfluid in the claim 1, wherein graphite granule can form steady suspension in fluid under the situation that lacks stablizer.

6. the microfluid in the claim 1, wherein graphite granule comprises graphite flake.

7. the microfluid in the claim 1, wherein graphite granule comprises the graphite of cleavage.

8. the microfluid in the claim 1, wherein the average largest cross-sectional sized that has of graphite granule is between 1 micron and 10 microns.

9. the microfluid in the claim 1, graphite granule concentration is between 0.01% and 2% volume(tric)fraction in its fluid.

10. the microfluid in the claim 1, graphite granule wherein kept stable suspersion at least one day in fluid.

11. the microfluid in the claim 1, its thermal conductivity strengthens at least 10%.

12. the microfluid in the claim 1, wherein the flakiness ratio of graphite granule was at least 10: 1.

13. a microfluid comprises:

At least a liquid in water or the alcohol and a large amount of graphite granules; The average largest cross-sectional sized of graphite granule is between 500 nanometers and 10 microns; Wherein graphite granule forms steady suspension in fluid.

14. the microfluid in the claim 13 further comprises a kind of basic material.

15. the microfluid in the claim 14, basic material wherein comprises a kind of oxyhydroxide.

16. the microfluid in the claim 15, oxyhydroxide wherein can make the part graphite granule functionalized at least.

17. the microfluid in the claim 13, fluid wherein is made up of water.

18. the microfluid in the claim 13, fluid wherein is made up of alcohol.

19. the microfluid in the claim 18, alcohol wherein comprises terepthaloyl moietie.

20. method; Comprise and add a large amount of graphite granules in a kind of fluid; The average largest cross-sectional sized of wherein a large amount of graphite granules is between 500 nanometers and 10 microns, and these graphite granules form steady suspension in fluid under the situation that lacks dispersion agent; In fluid, form the stable suspension of graphite granule.

21. in the method for claim 20, further be included in and add graphite granule to the preceding a large amount of graphite granule of cleavage of fluid.

22. a microfluid comprises:

A kind of liquid and a large amount of lamellas; Wherein the flakiness ratio of each lamella is at least 10:1, and the average largest cross-sectional sized of a large amount of lamellas is between 500 nanometers and 10 microns, and a large amount of lamella forms steady suspension in fluid under the situation that lacks sheet surfaces functional group.

23. a method provides a kind of particulate fluid that comprises, and the freezing formation of fluid is comprised the polycrystalline solid of crystal grain and crystal boundary; Wherein most of particulate largest cross-sectional sized are less than 10 microns, and particle thermal conductivity at least one direction when measuring for 25 ℃ is at least 5W/mK and/or specific conductivity is at least 10S/m; In freezing step, the part particle in the fluid is towards the zone migration of crystal boundary at least, and the granule density that is formed on the crystal boundary place is higher than at crystal grain inner.

24. in the method for claim 23, wherein in the refrigerated suspension medium, particle forms a network.

25. in the method for claim 24, particle forms an interconnective network

26. in the method for claim 23, particle wherein comprises that those specific conductivity and/or thermal conductivities at least in one direction are at least liquid electric conductivity and/or the material of thermal conductivity more than 5 times.

27. in the method for claim 23, wherein particle comprises nanotube, nanometer disk, nano flake, nano wire or nanometer filament.

28. in the method for claim 23, wherein particle comprises the carbon back particle.

29. in the method for claim 23, wherein particle comprises graphite flake, carbon nanotube, carbon nano wire or carbon nanometer filament.

30. in the method for claim 23, wherein particle comprises metal.

31. in the method for claim 23, wherein particle comprises metal nanometer line, metal nano fiber, metal nano dish, metal nano plate or metal nanoparticle.

32. in the method for claim 23, wherein particle comprises MOX.

33. in the method for claim 23, wherein most of particulate flakiness ratios were at least 3: 1.

34. in the method for claim 23, wherein fluid comprises water.

35. in the method for claim 23, wherein fluid comprises organic solvent.

36. in the method for claim 23, wherein fluid comprises alcohol.

37. in the method for claim 23, wherein fluid comprises hydrocarbon polymer.

38. in the method for claim 23, wherein fluid comprises n-Hexadecane, eicosane, triacontane, dodecyl, ten alkane, undecane, octadecane or pentadecane.

39. in the method for claim 23, fluid comprises hydrogel.

40. in the method for claim 23, fluid comprises metal.

41. a method provides the suspension medium that comprises first phase and the particle in suspension medium; Apply thermal gradient and/or electromotive force at the suspension-s two ends and allow suspension medium that the phase transformation of first to second phase takes place, make the thermal conductivity of suspension-s and/or specific conductivity change thus.

42. in the method for claim 41, most of particulate largest cross-sectional sized are less than 10 microns.

43. in the method for claim 41, particle thermal conductivity at least one direction when measuring for 25 ℃ is at least 5W/mK and/or specific conductivity is at least 10S/m.

44. in the method for claim 41, wherein suspension-s is the part of thermistor.

45. in the method for claim 41, wherein suspension-s is the part of TP.

46. in the method for claim 41, wherein suspension-s is the part of electrical fuses.

47. in the method for claim 41, wherein phase transformation is that resistive heating by suspension-s causes.

48. in the method for claim 41, wherein the thermal conductivity of phase transformation rear suspension liquid changes twice at least.

49. in the method for claim 41, wherein the specific conductivity of phase transformation rear suspension liquid changes 10 times at least.

50. in the method for claim 41, suspension-s bears 2 freeze/thaw cycles at least.

51. in the method for claim 41, wherein thermal conductivity and/or specific conductivity are not less than 20% in the variation of 5 freeze/thaw week after dates between first phase and second phase.

52. in the method for claim 41, wherein the composition of suspension medium has at least part to select based on the fusing point and/or the freezing point of composition.

53. in the method for claim 41, wherein the fusing point of the composition of suspension medium and/or freezing point are between-120 ℃ and 200 ℃.

54. in the method for claim 41, wherein suspended substance comprises liquid phase suspension-s, and phase transformation comprises and freezing.

55. in the method for claim 41, wherein suspended substance comprises solid composite material, phase transformation comprises thawing.