CN102753664B

CN102753664B - Electrically and/or thermally conductive suspensions including graphite microfluids

Info

Publication number: CN102753664B
Application number: CN201080063919.5A
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: 2014-08-06
Anticipated expiration: 2030-12-15
Also published as: CN102753664A; WO2011084481A1

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 graphite microfluid is led and/or thermal conductance suspension

Related application: the application requires the U.S. Patent Application No. 12/638135 of application on December 15th, 2009, patent name is that the right of priority of the United States Patent (USP) of graphite microfluid is also its part continuation case; The application also requires the U.S. Patent Application No. 12/720382 of on March 9th, 2010 application, patent name be the control that in suspension, thermal conductance and/or electricity are led United States Patent (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 is subject to American National Natural Science Fund In The Light (No.CBET-0506830) and subsidizes.Government has established right for the present invention.

Technical field

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

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 optimal running effect.Tradition enhancement of heat transfer generally adopts and in system, expands contact area (for example fin) and increase hot-fluid flow velocity.Yet traditional heat dissipating method many times cannot 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 suspends in the fluid of relative low thermal conductivity.This fluid except enough thermal conduction is provided, this fluid in low thermal conductivity requirement system, can significantly reduce the size of heat exchanger.

Prepare this high heat-conducting fluid and there is certain difficulty.For example, in a lot of examples, in some heat exchangers, be difficult to prepare a kind of stable high heat conduction suspension.Meanwhile, some material, as, the suspension 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 difficult to realize daily use because its price is very high.

Can control thermal conductance and/or electricity and lead and will there is good application prospect in a lot of fields, for example heating and refrigeration system, electric power distribution, sensing etc.Recent research has completed the preparation of high heat conduction and conductive fluid.This class fluid can be by suspending high heat conduction and/or high conductive material in relatively low heat conduction and conductive fluid.Once solid particulate is suspended in certain fluid conventionally, the heat conduction of suspension and conductivity no longer change with regard to being fixed.In routine use, have the needs to this system, this suspension does not need the electricity that just can change self by adding other any materials to lead and thermal conductivity.

Summary of the invention

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

Microfluid has been described in one embodiment.In some scheme, the fluid that microfluid comprises a kind of hydrophobic and a large amount of graphite granules, 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 to not carry out functional group's processing at graphite surface.

In certain embodiments, this microfluid comprises a kind of in water and two kinds of fluids of 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 stable 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 to not introduce any functional group on graphite flake surface.

In other embodiments, a kind of method has been described.In some cases, this method comprises in fluid adds a large amount of graphite flakes, 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 to not induce one on graphite flake surface.This method has further comprised and in fluid, has formed stable graphite granule suspension.

This method also comprises, in some cases, provides a kind of fluid that comprises particle, and the freezing formation of fluid is comprised to the polycrystalline solids of grain and grain boundary; In certain embodiments, wherein the largest cross-sectional sized of most of particles is 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, at least the part particle in fluid, towards the zone migration of crystal boundary, is formed on the granule density of grain boundaries higher than inner at crystal grain.

In some cases, this method comprises providing and comprises the suspension medium of first-phase and the particle in suspension medium; At suspension two ends, apply thermal gradient and/or electromotive force and allow suspension medium generation first-phase to the phase transformation of second-phase, make thus the thermal conductivity of suspension and/or specific conductivity change.

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

Accompanying drawing explanation

In unrestricted embodiment of the present invention, will illustrate by example and accompanying drawing, accompanying drawing is schematic 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 marks in every figure, each part in neither inventing in each embodiment is listed, because have the people of conventional knowledge not need schematic diagram to understand the present invention for this area.In these figure:

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

Fig. 2 is according to an embodiment, comprises the optics picture before one the 30 * graphite granule cleavage of amplifying;

Fig. 3 comprises a typical scanning electron microscope of cleavage graphite (SEM) displaing micro picture;

Fig. 4, according to one group of example, has comprised the schematic diagram of graphite granule;

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

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

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

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 region a in the graphite flake in Fig. 8 B; (D) concentration is the typical optics displaing micro picture of 0.2%V/V graphite suspension; (E) concentration is that 0.2%V/V graphite suspension is preserved a month later typical photo;

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

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

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

Embodiment

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

Fig. 1 is the schematic diagram of graphite granule microtexture, can be used in 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 by typical Van der Waals force with adjacent graphene layer, although there is the existence of a small amount of covalent linkage.In certain embodiments, the surface of Graphene can be oxidized, in some cases, can provide at least part of hydrophilic group.For example, in some cases, the graphite granule total hydrophilic that can become, or, graphite granule can become have amphiphilic.

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

Graphite is also a kind of super lubricant.Super lubricating is a kind of phenomenon known in the art, and the frictional force that refers generally to two planes approaches, but do not reach zero.In microfluid super lubricant for example the use of graphite can effectively make frictional force in microfluid keep a very low value.Low-frictional force fluid can be realized the Efficient Cycle of fluid by relatively low pump power, reduce the damage to moving parts surface in equipment simultaneously.In addition, low friction, high heat-conducting fluid can both need effectively lubricating also to need the occasion of high heat transmission to realize dual-use.Do not wish to be subject to the restriction of any theory, the super lubrication of graphite comes from interlayer magnetism lower in graphite (for example, Van der Waals force).

Graphite granule can be comprised of the graphite that is much applicable to type.In certain embodiments, graphite granule can comprise or prepare from natural graphite.Fig. 2 has provided the typical graphite optics picture that amplifies 30 times.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 flat with what isolate, and dish shape particle exists.If keep complete, there are six side borders, after destroying, there is irregular or horn shape border.In some cases, natural graphite comprises amorphous graphite (being also carbonization hard coal), and this is also conventionally our said graphite.Its graphite granule comes from the rotten of coal, and exists with tiny particle.In this area, usually very tiny flake graphite is called to amorphous state.In addition, natural graphite comprises blocky graphite (referring to vein graphite), and it usually occurs in crack mineral ore or breaking part, with raw crystalline aggregate micro-or needle-like in a large amount of, exists.

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

In certain embodiments, graphite granule comprises cleavage graphite.Fig. 3 is the electron microscope picture of typical cleavage graphite in 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, and 50 times, 100 times, 300 times, or 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, or at least 500 times to the density of its initial graphite granule (being graphite flake).

Graphite granule described herein comprises the carbon (wt is mass parts for 95wt% at least, 99wt% at least, or 99.9wt% at least) of relative high-content, 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 (as metal, doped 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 situations.Intercalated graphite has superconduction ability (can reach zero resistance).

Although the embodiment here has 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 the common phenomenon in a kind of this area that base dissociates, and refers generally to Crystal Cleavage face and is parallel to base plane.These materials include, but are not limited to mica (biotite for example, white mica, phlogopite, lithionite, margarite, glaukonine etc.), clay mineral matter (kaolinite for example, illite, polynite, montmorillonite, vermiculite, talcum, magnalium skin stone, pyrophyllite, etc.) and other materials.

In certain embodiments, graphite granule is micro-meter scale.The selection of graphite size is all important to the raising of the heat conductivility of graphite microfluid stability and fluid, for example, relative centimetre or big scale particle more, micron-scale particle easily suspends in fluid.In addition, micro-meter scale suspension is not easy blocking heat-exchanger pipeline.At some, be in embodiment, the average largest cross-sectional sized of micron graphite particle 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, in Fig. 4, graphite granule 20 has width 22 and thickness 24.Maximum cross section is 26.The average cross-sectional dimension of particle refers to the mean number of these particle cross-sectional dimension.The scanning electron microscopy picture (SEM) that a big or small common method of test largest particle cross section is analysing particulates.

In some embodiment, in microfluid, the yardstick of the graphite of relatively high per-cent is micron order.For example, in certain embodiments, volume fraction is at least 80%, 90%, 95%, or the cross section of 99% graphite granule is between 500 nanometers to 10 micron, between 1 micron to 10 microns, or between 1 micron to 5 microns.

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

In certain embodiments, other shapes graphene-based particle of this microfluid except sheet.This graphene-based particle may comprise, the formations such as for example micron tube, or micron cone.Should be noted that other shapes also may occur.Do not wish limited any theory, micron tube and micron cone are perhaps that graphene film is because inner tensions is rolled formation.

In some instances, graphite granule described herein can functionalised and be with corresponding functional group.The people in this area with conventional technical ability will be understood that the implication of phrase " functional group ".Functionalisation of surfaces does not comprise the surface (allow graphite be exposed in oxygen, allow the some or all of surface of graphite be oxidized) of graphite oxide.In certain embodiments, hydrophobic graphite granule can surface functionalization, becomes relative water-wetted surface, can stable suspersion for example, at water seeking liquid, in water and alcohol.For example, after oxidation, graphite granule can form hydroxy functional group.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 adjusting graphite surface, will be described in detail below.In certain embodiments (for example, when microfluid comprises water seeking liquid, for example water and ethanol), functionalization graphite granule can improve the stability of graphite granule suspension, or forms stable suspension, anyway form unstable suspension.

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

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, ethylene glycol etc.), water, or the mixture of water and alcohol.In some instances, this microfluid comprises oil (for example, poly-alpha-olefin(PAO) oil, silicone oil, mineral oil, synthetic oil, oxide glycol/propylene oxide synthetic oil, the synthetic wet goods of poly-alkane glycol).In some instances, also may use other oils.The user that the selection of base fluid type mainly depends on this microfluid to.

In some cases, this microfluid comprises hydrophylic fluids (such as 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 stable water and liquid mutually.

(for example when microfluid comprise hydrophobic liquid, oil) in some cases, graphite granule for example can lack on surface, in the situation of functional group's (phenyl, carbonyl etc.) stable suspersion in fluid.In some cases, graphite granule can be under the effect that there is no surface dispersant stable suspersion in this fluid.In a situation, graphite granule not under the effect of all stablizers in this fluid stable suspersion.Here stablizer refers to any entity that can improve graphite granule stability in suspension.In the situation that lacking stablizer, graphite granule also can stable suspersion, but need to be under identical adjusting (being temperature, pressure condition etc.).Typical stablizer comprises, tensio-active agent for example, acid, base material, the stability functional group of graphite surface (for example phenyl, carboxyl) etc.

For example, in certain embodiments, the suspension that microfluid comprises stable graphite granule, and graphite surface does not have functional group's (or/and tensio-active agent, or/and stablizer).In some instances, microfluid may comprise functional group's graphite granule (or/and tensio-active agent, or/and stablizer), but when there is no these stablizers, graphite still can form stable suspension by stable suspersion.In some cases, the functional group of these graphite surfaces (or/and tensio-active agent, or/and stablizer) perhaps the suspension of graphite granule is not had to materially affect.In other cases, the functional group of graphite surface (or/and tensio-active agent, or/and stablizer) stability of suspension is had to some effects, but be not enough to form stable suspension due to the appearance of these stablizers.A special case, microfluid can for example, be suspended and form by graphite granule in oil (PAO oil).Graphite granule can be under the effect that there is no phenyl and/or carboxyl surface functional group stable suspersion in oil.A small amount of phenyl is or/and carboxyl can then be added in the graphite surface in microfluid.In this example, graphite granule is still said does not need functional group can form stable suspension, due to microfluid stable suspersion just before functional group forms.

Although in certain embodiments, microfluid does not comprise tensio-active agent, and in other embodiments, perhaps these microfluids comprise one or more tensio-active agents, polyvinyl alcohol polyvinyl alcohol(PVA for example), polyvinylpyrrolidone poly-vinylpyrrolidone (PVP), 12 (alkane) base 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, wishes to be not restricted to any theory, and the thermal conductivity of the microfluid is here because graphite High directional thermal conductivity coefficient causes.Meanwhile, by 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 inserting between particle) is less, and micron order graphite-phase is to nano graphite flakes, and the thermal resistance that hot-fluid is encountered is relatively less.

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, or 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, or is at least 3.0.Relative thermal conductivity is expressed as:

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

In formula, the thermal conductivity of the microfluid that K represents to comprise 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 graphite divided by the thermal conductivity of water.

In certain embodiments, the raising of the thermal conductivity of microfluid can reach and be at least 25% with respect to the neat liquid that there is no graphite granule, 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 formula ₀the same as described above.

The thermal conductivity of liquid can be measured by transient state hot wire process, 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 flow thermal conductivity coefficient, a diameter is that 50 microns of platinum filaments (there is the thick insulation layer of 25 microns on its surface) immerse in testing liquid completely.The impulse of current of accurately knowing is by hot line, and the temperature of generation raises and measures over time by resistance in monitoring heated filament.The thermal conductivity of liquid solves thermal conductivity equation by analysis transient temperature variation profile and obtains.

Under many circumstances, with respect to the base fluid specific conductivity without graphite granule, the specific conductivity of microfluid also can improve.For example, the specific conductivity of microfluid can at least 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, or at least 10000000 times.In certain embodiments, the specific conductivity of this microfluid is at least 0.001, is at least 0.01, is at least 0.1, is at least 1s/m, or is at least 10s/m.In certain embodiments, the specific conductivity of microfluid is at least 100 times of base fluid specific conductivity, is at least 500 times, is at least 1000 times, is at least 10000 times, is at least 100000 times, is at least 1000000 times, or at least 10000000 times.

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

On the one hand the preparation method of this microfluid is illustrated.This method comprises a large amount of graphite granules is added in liquid, forms stable suspension.Graphite granule possesses one or more features discussed above.In addition, whether suspension has stablizer, or stablizer, be before graphite granule suspends, add or suspend after add.

In certain embodiments, the process choosing ground of formation microfluid comprises graphite granule pretreatment process.Graphite granule is manufactured by suitable technique.For example, graphite granule can pass through intercalation or expansion natural graphite, grind, and spheroidal graphite, the methods such as electroless plating are produced.In one group of embodiment, graphite granule can be by cleavage.In this process, graphite is heated to high temperature (being generally 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, in graphite cleavage process, to add a kind of acid (for example sulfuric acid).Once 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, or at least 500 times.Accordingly, the volume of graphite, on the basis of original graphite, has reduced at least 50 times, and at least 100 times, at least 300 times, or at least 500 times.In certain embodiments, in the attenuating of graphite granule density, follow buoyancy to improve the suspension that has improved particle.Expanded graphite can add in fluid, and (being ultrasonic wave) processes to carry out sound wave subsequently.In some cases, graphite granule can be dry state, and can again disperse in 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 is peeled off, particle surface may comprise phenyl, epoxy group(ing), carboxyl etc.Be not restricted to existing any particular theory, remaining functional group for example can be, due to chemical graft (sulfuric acid, or other strong acid, oxygenant etc.) or the product in stripping process.In some cases, after stripping process, in graphite granule or graphite microfluid, substantially do not need to add any material (for example, there is no the functional group of graphite surface, there is no tensio-active agent, there is no stablizer).For example, in some cases, graphite granule is stripped from, and the particle being then stripped from can directly add in liquid and form and stablize graphite microfluid, and does not need to add any functional group, or acid, alkali, tensio-active agent, or other stablizers.In certain embodiments, graphite is by after stripping process, and graphite granule can directly form stable suspension, does not need to add any material (comprising acid, alkali, tensio-active agent, functional group etc.).For example, in many situations, after graphite is stripped from, a kind of acid, a kind of functional group, or other stablizers may be added in graphite and (also comprise acid treatment process), but graphite granule still can form stable suspension, even without acid or other stablizers.In many situations, acid, adding of alkali or other materials, does not have Effect of Materials to the stability of graphite granule suspension.

As mentioned above, system and method described herein can be for the preparation of thermal conductivity and/or electroconductibility enhance fluid, and relevant similar non-graphite microfluid.This class fluid can find some special purposes, for example, and in heat exchange system.Effectively heat transmission is conducive to carry out effectively cooling with relatively little interchanger.In addition, this microfluid also can be used as 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 is wound around and causes two to be separated.And micron graphite particle described herein relatively easily suspends, due to the little (2-2.2g/cm of density ³) and surface-area large or/and larger surface charge density.And graphite granule has thermal conductivity (about 1000W/Mk or more) in larger face.And relative carbon nanotube and other nano materials, micron graphite particle is relatively cheap.Graphite is also a kind of natural lubricant, can reduce the surface damage (for example figure layer of workpiece surface) with the device of fluid contact.Finally, the large-size of micron graphite (with respect to nano particle) be conducive to 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 Transport

The present invention relates to and control suspension thermal conductance and electric article of leading, system and method is also done general description at this.In certain embodiments, the suspension that comprises particle at some has variable thermal conductance and/or electricity lead (for example, particle can improve thermal conductance and or electricity lead).Here the thermal conductivity of suspension and/or electroconductibility can change by the phase transformation of suspension (for example, solidify or melt).For example, thermal conductivity and/or electroconductibility can improve by solidifying of suspension.In certain embodiments, comprise in the fluid process of setting of suspended particle and can form polycrystalline, comprise crystal boundary and crystal grain.Once after fluid solidifies, the particle in fluid can move to crystal boundary and gets on and cause the density of the particle on crystal boundary to be obviously greater than the density of crystal grain internal particle.On crystal boundary, the particle of high density has just formed particle network, as described below.

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

According to one group of embodiment, Fig. 7 A-7C has set forth the schematic diagram of suspension phase transition process.In Fig. 7 A, particle 110 is suspended in fluid 112, forms stable suspension.As shown in Figure 7 A, these particles have all been distributed in medium substantially.In other embodiment, when suspension medium is liquid, these particles may form a large amount of clusters in fluid.In certain embodiments, when suspension is under liquid state, these particles may form chain-like structure (for example, causing owing to solidifying with thaw cycle) in fluid.

In certain embodiments.Can there is one-level or multi-level phase change (for example, solidify and melt) in the medium in these suspension, these are compared thermal conductance or the electricity that process can change suspension and lead.For example in some cases, a kind of suspension of liquid state (suspension that comprises liquid medium) can solidify and form mixture (suspension that comprises particle and solid dielectric).The suspended substance here should be appreciated that it is that liquid suspension can be also solid-state matrix material.Fig. 7 B is schematic diagram after Fig. 7 A suspension solidifies.Once freezing, fluid 112 forms polycrystalline solids suspension medium, comprises 116 crystal grain and 118 crystal interfacies, so form solid composite.In refrigerating process, these particles can move to crystal boundary, make the granule density of grain boundaries significantly be greater than the endocorpuscular concentration of crystal grain.These particles have formed the network (being exactly an interconnective network of particle) of particle to the migration of crystal boundary.Fig. 7 B has provided the schematic diagram that particle 110 moves to polycrystalline crystal boundary 118 and forms network.

In some cases, this solid state composite (suspension solidifying) is liquid suspension relatively, has very large 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, or between 2 times at least 5 times.In some instances, the electroconductibility of solids suspension is at least at least 2 times of liquid suspension, 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.Be not subject to the restriction of other any particular theory, this solid union material has relatively large heat conduction or electroconductibility is due to particle gathering on crystal boundary (and internal stress), and gathering of this particle high density caused the formation of heat conduction or conductive network that heat and/or electric energy are effectively transmitted.The thermal conductivity of fluid or suspension can be by 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 formation liquid suspension.Fig. 7 C comprises that in Fig. 7 B, solids suspension melts the schematic diagram of rear formation liquid suspension again.In Fig. 7 C, particle 110 is dispersed in (being liquid 112) in liquid medium.As shown in Fig. 7 C, these particles are homodisperse.But in certain embodiments, it is network-like that these particles still keep, at least after melting, suspension medium keeping to a certain degree these networks.In some cases, these particles focus on formation cluster in a large number, and in other cases, after suspended substance melts, particle still keeps some network structures.

With respect to solid composite material, melt and can reduce its suspension thermal conductivity and/or electroconductibility.In certain embodiments, extremely when young 2 times of the thermal conductivity ratio solids suspensions of the liquid suspension after thawing, to when young 3 times, to when young 5 times, between 2-10 times, or between 2-5 times.Under certain conditions, the liquid suspension after 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 re-dispersed in medium institute extremely.

Under certain conditions, the later liquid suspension liquor ratio after again melting solidify before heat conduction and/or the electroconductibility of liquid suspension want high.For example, the first liquid phase suspension that has in some cases the first specific conductivity and the first thermal conductivity solidifies and forms solid union material.Subsequently, this solid state composite can melt and form second liquid suspension, and this second liquid has higher thermal conductivity and/or electroconductibility than first liquid suspension.Be not limited to existing any theory, the thermal conductivity of the second liquid suspension (suspension again melting) and/or electroconductibility are because still have the coacervate (having formed the network of particle) of some particles in second liquid suspension of solids suspension after dissolving than first liquid suspension height.In some cases, the heat conduction of these second liquid suspension 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 (solidifying/thaw cycle).In certain embodiments, suspension variation of (circulation is for the first time except rear) heat conduction and electroconductibility after the phase transformation circulation through repeatedly solidifying and melting is tending towards constant.For example under certain conditions, in the phase transformation of solid-liquid two-phase, the variation of heat conduction and electroconductibility is at least 20%, be at least 10%, be at least 5%, be at least 1%, or substantially keep identical multiple to change at least at 2, at least at 5, at least at 100, at least at 1000, or solidify after thaw cycle more.Should be realized that a solidify/thaw cycle comprises that suspension becomes transformation solid-state and from solid-state to liquid from liquid state.

Particle described herein can be comprised of a lot of suitable materials.For example under certain conditions, particle can be comprised of metal, can be pure metal or alloy.Under certain conditions, metal can be nanoscale particle.This metallic particles comprises, metal nano-tube for example, metal nanometer line, metal nano dish, nano metal sheet, or nano metal fiber.In certain embodiments, due to 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 metal oxides.

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

In certain embodiments, carbon back particle is used.Under certain conditions, carbon back particle comprises aromatic condensed ring network, and particle consists of basic carbon atom.A kind of aromatic condensed ring comprises at least 10, at least 50, at least 100, at least 1000, or at least 10000 aromatic nucleus.In certain embodiments, carbon back particle comprises relatively high carbon content (wt is mass parts for 95wt% at least for example, 99wt% at least, or 99.9wt% at least), and carbon content is calculated and do not comprised any other functional groups that are connected on particle.Carbon back particle condensed ring end may comprise arbitrarily some borders.For example, a slice Graphene comprises a plane one of carbon tip, and carbon nanometer comprises an on-plane surface end nanostructure.Under certain conditions, these end structures are replaced by hydrogen atom.In some cases, these end structures are included the group replacement (for example phenyl) of Sauerstoffatom.The example of carbon back particle 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, carbon back particle is because self has lot of advantages compared with high heat conduction and conductive capability.

In certain embodiments, the particle in suspension can be graphite granule, 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 be made 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 of mentioning in this patent.

Use graphite to be beneficial to especially preparation low viscosity suspension.As mentioned in literary composition, graphite also can be used as super lubricant.The super lubricated frictional force between two surfaces that refers to, approaches but non-vanishing phenomenon.The use of super lubricant (for example graphite) can keep lower frictional force in suspension.And low-frictional force fluid allows relatively little pump horsepower to carry out Efficient Cycle, and reduce the effective damage to moving parts in equipment.In addition the high thermal conductance fluid of low friction has dual function concerning needing the application of effectively lubricating and efficient heat transfer.Not with other conflict of theories, this super graphite lubrication effect is because reactive force less between graphene layer (being Van der Waals force) causes.

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

In some cases, the cross-sectional dimension of most of particles is less than 10 microns.As mentioned before, maximum cross section refers to that some graphite flakes can measure the ultimate range on two borders.So average maximum cross section refers to graphite flake and can measure several mean values of two ends ultimate range.The method of a general test maximum cross section size is to analyze SEM photograph.In certain embodiments, the cross-sectional dimension of most particles is less than 1 micron, is less than 100 nanometers, or between 1 nanometer-10 micron, between 10 nanometer-10 micron, or between 1 nanometer-1 micron, or between 1-100 nanometer.

In some cases, in suspension, the yardstick of most of particles is micron order.For example, in certain embodiments, at least 80%, at least 90%, at least 95%, or at least 99% particle to have maximum cross section be at least 10 microns, 1 micron, at least 100 nanometers, or between 1 nanometer-10 micron, between 10 nanometer-10 micron, between 1 nanometer-1 micron, between 10 nanometer-1 micron, or between 1 nanometer-100 nanometer.

In certain embodiments, these particles have larger flakiness ratio.For example, these particles are comprised 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 cone, nanotube, nano wire, nanofiber, nanocone and similar structures.The thickness of these structures is all less than the size of length direction substantially.In certain embodiments, great majority 80%, at least 90%, at least 95%, or two quadrature Length Ratios of at least 99% particle are at least 3: 1, be 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, or be at least 10000: 1.

In certain embodiments, these particles have larger thermal conductivity at least in one direction.In some cases, these particles are at least in a direction, and thermal conductivity is at least 10W/mK, is at least 50W/mK, is at least 100W/mK, 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, the thermal conductivity of these particles (at least one direction) is at least 5 times of base fluid thermal conductivity in suspension, at least 10 times, at least 100 times, at least 1000 times, at least 10000 times, at least 20000 times, or 5-20000 doubly, 10-20000 times, 100-20000 times, or 1000-20000 is doubly.

In certain embodiments, these particles have relatively high 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, 1000S/m, and 10000S/m, 100000S/m, 1000000S/m, probe temperature is 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 for example, is led efficiency far at the thermal conductance of first direction (and/or more multi-direction, direction in the face in lamellar structure) and/or electricity and is greater than second direction (being the direction of vertical first direction).Here it is anisotropic conductor.Thermal conductance and/or electricity are led more effective first direction, refer to the direction (being parallel and direction Graphene plane) along particle length direction.The thermal conductance of second direction and/or conductance ratio first direction are low, refer to the thickness direction (direction that for example graphene film multilayer is intersected) of particle.In certain embodiments, as fruit granule first direction is longer than second direction, this particle is exactly highly heat-conductive material in face.This anisotropic conductive material comprises, graphene film, graphite granule, carbon nanotube, carbon nano wire and analogous material.

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

Any suitable fluid (for example, liquid, colloid) may be used to the base fluid of suspension.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 cross-linked polymer chain, no matter is directly cross-linked or is cross-linked by linking agent.In some cases, can change this degree of crosslinking, and change the ability of its receptivity and reservation water.The polymer that can form hydrogel comprises containing polymeric silicon, polyacrylic ester, and cross-linked polymer is (for example, polyethylene oxide, polymeric amide and PVP (PVP), polyvinyl alcohol, acrylate polymeric (for example, sodium polyacrylate) and hydrophobic multipolymer

In certain embodiments, suspension medium is solid (for example, polycrystalline solids).This suspension medium can obtain by frozen liq.If polycrystalline solids is expected results, the liquid that can form by solidifying polycrystalline obtains.Conventional identification liquid solidifies a method that whether forms polycrystalline solids, can be for screening fluid, and for example, then freezing a kind of fluid carries out suitable crystal structure analysis.A kind of method that whether forms polycrystalline after conventional identification fluid solidifies is X-ray diffraction method (XRD).

Suspension medium comprises the composition that any form is suitable (not considering its phase).For example, the medium of this suspension comprises organic or inorganic components.These compositions including, but not limited to, water, alcohol (for example, ethylene glycol, ethanol), the combination of hydrocarbon polymer (for example, n-Hexadecane, eicosane, tridecane, dodecane, undecane, ten alkane, octadecane, pentadecane) or these materials.Under certain conditions, the medium of these suspension comprises water seeking liquid (for example, water, alcohol etc.).In general, hydrophobic nature and wetting ability refer to that a kind of fluid is whether can be under the effect that there is no tensio-active agent or other stablizers miscible and form the feature of stabilized mixture with water.In certain embodiments, high-melting-point substances is also contained in suspension medium relatively.For example, in some cases, suspension medium can comprise a kind of metal.For example, liquid can comprise scolder, as tin, and copper, silver, bismuth, indium, zinc, antimony, the mixture of lead and/or these metals.In some cases, also may use other fluids.Use which kind of fluid to depend on the purposes of this suspension.

In certain embodiments, the selection of the composition in this suspension medium is to depend on the zero pour of this composition and/or molten point (the zero pour is here different with molten some temperature) at least partly.For example, the selection of the composition of this suspension medium is due to its zero pour and/or molten for example, at some distinct temperature scope (between-120 ℃～200 ℃).Under certain conditions, the selection of this certain composition of suspension medium is to approach envrionment temperature or slightly low due to its zero pour and/or molten point.This suspension can be applied in some equipment to sensitive.Under certain conditions, the selection of the composition of this suspension medium is due to its zero pour and/or molten between-120 ℃～40 ℃, between-20 ℃～40 ℃ degree, between-5 ℃～40 ℃, between 0 ℃～35 ℃, between 15 ℃～25 ℃ etc.This by selecting the method for different zero pour and molten some medium can change phase transformation (therefore changes thermal conductance and electricity the is led ability) temperature of suspension, and be applied in some place especially.For example, water can be near temperature detection sensor 0 ℃.Another one example, n-Hexadecane, zero pour/molten point is 18 ℃, can be for detection of the sensor near room temperature.

Here said suspension comprises the particle of all suitable concns.In certain embodiments, the particle concentration volume fraction that suspension comprises is lower than 2%, or lower than 1%, or at 0.01%-2%, or between 0.05-2%, or between 0.1-2%, or between 0.5-1%, or between 0.6-0.9%, or between 0.7-0.85%.In certain embodiments, also can the suspension of compound particle concentration outside above-mentioned category.In industry, a conventional technology is the volume fraction of nano particle in calculating suspension.For example, when metering, first need to weigh the quality of particle.The volume of particle then can be by the quality that weighs divided by the density calculation of particle out.Then, the volume that the volume fraction of nano particle can be by particle calculates divided by the volume (the volume sum of particle and liquid medium) of suspension.

In certain embodiments, can in suspension or its solid-phase construction, apply voltage.For example,, when suspension, may play a role during as thermistor a part of at it.In certain embodiments, suspension may be as temperature sensor.In certain embodiments, when electromotive force is applied to liquid suspension two ends, its specific conductivity is lower.When being exposed at relatively low temperature, suspension solidifies, and the solid phase matrix material of formation will have higher specific conductivity.Under solid phase, higher specific conductivity will allow electric current by suspension, for example can be for the driving of atmosphere control system.The common skill that Certainly is in the industry to form temperature sensor by this solid phase matrix material, when it is exposed at sufficiently high temperature, can melt, and cuts off electric current thereupon.As another one example, this suspension can be used as current fuse.In certain embodiments, applying electrical potential can be clipped in the solid phase matrix material two ends that specific conductivity is higher, and electric current is passed through from matrix material.After electric current surpasses threshold value, solid phase matrix material can melt due to resistance heating (being joule heating).After melting, solid phase matrix material has the liquid phase of relatively low conductivity suspension by becoming.In suspension, relatively low specific conductivity will cause the electric current wherein passing through significantly to decline (or cut-off), plays thus the effect of fusible cut-out.

In some cases, the gradient of heat may for example, by suspension (liquid suspension, solid union material, or have both at the same time).For example, thermal gradient may be applied on the solid union material with higher heat-conductivity, causes heat to flow through solid composite material.If the temperature of solid composite material exceeds critical level, it will melt, and cause forming having the liquid suspension compared with lower thermal conductivity.The relative low-heat conductance of liquid suspension may cause by the reduction of the hot transmission quantity of suspension, and for example this, may protect the temperature sensor in suspension downstream.

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

Suspension described herein can obtain by any suitable method.In certain embodiments, suspension can be by getting up to obtain (for example,, by adding particle or add liquid in liquid in particle) by 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 of particle.For example, relatively the particle of hydrophobic can become relatively hydrophilic by functionalized its surface that makes, and can form stable suspension in as water and alcohol at water seeking liquid.In addition, relatively hydrophilic particle can be by functionalized its surface relative hydrophobic that becomes that makes.The surface of particle can be functionalized by a large amount of different functional groups, for example, comprise hydroxyl, carbonyl, epoxy group(ing) etc.

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

Suspension described herein may be to consist of stable particle suspension liquid in some cases.For example, in some instances, particle can stably be suspended in liquid suspension medium at least one day, at least one week, and January at least, June at least, or at least one year.Generally speaking, a stable suspension is a kind of suspension that does not have substantive solids precipitation to occur within the time cycle of its use.Form the system and method for this stable graphite suspension in other patents, for example, in the United States Patent (USP) " graphite microfluid " that is 12/638,135 at the number of patent application of on December 15th, 2009 application, have similar description, 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 will provide one or more superiority.For example, compare with the similar device based on electronics, the device of manufacturing based on suspension is relatively quick and cheap.In addition, this system based on suspension can be near room temperature execution work, and can just can change by changing simply the composition of suspension medium the execution temperature of device.The system of the suspension base in temperature or current control system also can be simply transported to another position by pump or other the fluid hierarchy of control from a position.

Example below 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, production and the test of graphite microfluid have been described.Natural graphite comes from Asbury Carbons company (Asbury Graphite Mills, Inc., NJ, USA).The chemical oxidation process (Carbon 43(2005) that uses the people such as Tryba to propose, pp.2397-2429, for all considerations, the document is done as a whole indexed) natural graphite is used for producing graphite intercalation compound.The hydrogen peroxide of different volumes mark (from 0 to 30%) and sulfuric acid H ₂sO ₄mix, prepare the oxygenant of intercalation technique.The natural graphite of 2.2 grams at room temperature reacts 30 minutes with the oxygenant of 100 milliliters.The slurry having reacted rinsing in deionized water reaches 6 to 7 to pH, is then placed on hot platform 80 ℃ of bakings 24 hours.Then graphite heats 5 seconds to 180 seconds in Haier's microwave oven of 1100W, compares with original size, and the volume of graphite will expand over 300 times.Then the graphite after expanding is added into the graphite granule that in solvent, ultrasonic dispersion suspends with generation for 15 to 120 minutes.

Start, measured the impact of graphite granule concentration on thermal conductivity.Polyalpha olefin synthetic base oil (" PAO "), ethylene glycol and water are used as the liquid phase part of microfluid.Volume fraction is respectively 0.1%, 0.3%, 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 thickness insulation layers is 50 microns is immersed in sample completely.In platinum filament, by the accurate pulsed current of dose known amounts, the function that the temperature causing rising is used as the time detects by monitoring the variation of resistance in platinum filament.By adopting the solution 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 respectively thermal conductivity figure and the thermal conductivity enhancing figure of the microfluid sample with different graphite particle volume fraction.In all three fluids, when being 1% volume fraction, graphite granule concentration all shows the thermal conductivity increase that surpasses 100%.As shown in Figure 5 B, the graphite granule that adds 1% volume fraction surpasses 1.27W/mK to improving its thermal conductivity in water, and when the increase of thermal conductivity reaches high 110%(corresponding to 25 ℃, deionized water thermal conductivity (0.6W/mK) surpasses the relative thermal conductivity of 2.1 times).In addition, Fig. 5 A-5B has illustrated that thermal conductivity presents nonlinearities change along with the variation of graphite granule volume fraction, and when higher graphite granule volume fraction, thermal conductivity improves increasing.

Then, the specific conductivity of ethylene glycol microfluid is measured.Volume fraction is respectively 0.01%, 0.02%, 0.03%, 0.05%, 0.07%, 0.85%, 0.1%, 0.2%, and 0.3% graphite granule is added in ethylene glycol.In addition the specific conductivity of pure glycol sample is also measured.Fig. 6 has comprised the specific conductivity (on logarithmic axis) of 9 test samples.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 fraction graphite granule microfluid, has increased by four orders of magnitude.

Embodiment 2

This example has been described by the electricity of phase transformation controlled material and thermal property.Use graphite-n-Hexadecane suspension, the specific conductivity of material can change two orders of magnitude at 18 degrees Celsius, and thermal conductivity can change three times.

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

Expansion form rear and cleavage graphite flake layer is observed by scanning electron microscope (SEM) (EOL JSM-6320).The microstructure of cleavage graphite is at room temperature observed by 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 may be because the internal stress of bringing out in preparation process causes.Fig. 8 C is the high resolution scanning Electronic Speculum figure in region in figure B " a ".Can find that this graphite flake comprises about 30 layers of atom, about 0.335 nanometer of average layer spacing, with the data consistent of observing in graphite.Fig. 8 D is that volume fraction is the light micrograph of graphite/n-Hexadecane suspension of 0.2%.From this photo, can observe graphite flake and form three-dimensional Percolation network.In light micrograph, ambiguous region is due to non-coplanar graphite flake layer overfocus or owe Jiao and cause.The formation of Percolation network shows the formation of dense thick graphite/n-Hexadecane suspension.Fig. 8 E is that graphite/n-Hexadecane suspension of 50 milliliter 0.2% is being prepared rear trimestral photo.Can find out that suspension is highly stable, in suspension, not see in fact precipitation.

The resistance of suspension is that these box two ends are vertically inserted with area 1.17cm2, the copper electrode that spacing is 4.85 centimetres by suspension being poured in a homemade conductive box.The system resistance of this conductive box is approximately 0.8 ohm.The electricity of graphite suspension is led by following formula and is calculated:

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

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

The thermal conductance measurement of graphite suspension is to use Nagasaka and Nagashima(J.Phys.E:Sci.Instrum.14,1435(1981)) the transient state hot wire process of development measures.The platinum filament that diameter that has applied 25 micron thickness insulation layers is 50 microns is immersed in sample completely.In platinum filament, by the accurate pulsed current of dose known amounts, the function that the temperature causing rising is used as the time detects by monitoring the variation of resistance in platinum filament.By adopting the solution 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 are changed significantly at 18 ℃.Fig. 9 A is specific conductivity and the temperature relation figure of graphite suspension.Under liquid state, the specific conductivity of graphite suspension is along with the variation of temperature is almost constant.When temperature is between 17.5 ℃ and 18.5 ℃, specific conductivity increases about two orders of magnitude.After n-Hexadecane freezes, specific conductivity settles out again.In solid-state and liquid state, specific conductivity all increases along with the increase of content of graphite.Yet as shown in Figure 9 B, the specific conductivity of suspension after freezing and the ratio of the specific conductivity of liquid suspension (this numerical tabular understands the increase of the freezing specific conductivity causing) reach the peak value of 250 times when the volume fraction about 0.8% of graphite.

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

In order to obtain the clear image of graphite/n-Hexadecane suspension Monte Carlo method in freezing and ablation procedure, we have used the suspension sample (0.05% graphite/n-Hexadecane) of a dilution.Under liquid state, graphite flake is evenly dispersed in n-Hexadecane relatively.In some cases, a part of graphite flake adsorbs mutually, forms graphite cluster.In Fig. 9 E, the region of black is corresponding to graphite cluster, and n-Hexadecane crystal demonstrates the structure of needle-like.In freezing process, graphite flake is shifted onto grain boundaries by the n-Hexadecane needle-like crystal of anisotropic growth, generates a kind of three-dimensional Percolation network (Fig. 9 F).When freezing n-Hexadecane melts again, except graphite Percolation network still exists, 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 hot variation.When freezing for the first time time, most of graphite flakes have been pulled to grain boundaries, have formed the Percolation network of close contact, have increased the contact area of graphite flake, have reduced heat and electric contact resistance.When freezing n-Hexadecane melts again, the contact area between graphite flake reduces rapidly.Yet many graphite flakes are limited in Percolation network, only have relatively less graphite flake to be suspended in the liquid of thawing.With respect to original suspension, the specific conductivity of the suspension heavily melting 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 in situation.

The specific conductivity of graphite suspension and the velocity of variation of thermal conductivity show the density dependent with graphite cluster.When graphite flake is transported to grain boundaries, the growth of n-Hexadecane crystal has promoted the formation of cluster.When graphite volume fraction is lower, many clusters isolate.Along with the increase of graphite volume fraction, increasing graphite cluster couples together, direct liquid and solid-state between the ratio of conductivity (comprising electricity and heat), as shown in Fig. 9 B and 9D.When graphite volume fraction further increases, graphite cluster 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, this is by the pressure decreased that n-Hexadecane crystalline anisotropy growth is caused.Result is observed the maximum variation of liquid and solid-state lower specific conductivity and thermal conductivity when graphite volume fraction 0.8%.

Figure 10 has shown a room temperature experimental installation, is used for measuring the contact resistance of two graphite flake layers that strip down under n-Hexadecane environment.Polyethylene vessel that comprise liquid n-Hexadecane are as container.Two graphite flake layers are immersed in n-Hexadecane, and each graphite flake is connected with volt ohm-milliammeter by the gold thread of 30 microns of diameters.Graphite flake is to strip down from high pyrolytic graphite (HOPG SPI-1, SPI Supplies company).The size of graphite flake is approximately 3 centimetres of 1 micron * 3 cm x.Graphite flake contacts by adjusting the position of gold thread.Temperature and the resistance of this device are measured by volt ohm-milliammeter.The internal stress of n-Hexadecane is measured (Pressures, Sensor Products company) by ultralow pressure characterization of membrane, and data are analyzed by Topaq software (Sensor Products company).The high pyrolytic graphite of peeling off is crooked uneven.When they are close to each other, contact area is very little, makes thus the resistance between graphite flake very high.There is strong anisotropic growth kinetics in n-Hexadecane, between different crystal orientation, gap is over 10 times.In n-Hexadecane refrigerating process, can form needle-like crystal, its slenderness ratio depends on chilling rate.Do not wish to be limited to any particular theory, the anisotropic growth of n-Hexadecane crystal may show to produce pressure at graphite flake, has increased fast their contact area.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 due to the repulsion fast-descending between elastic recovery and particle (Figure 11 A).When temperature drops to 17.5 ℃ from 18.5 ℃, the resistance of electric current declines 460 times, as shown in Figure 11 B.Figure 11 C is the stress pattern in freezing n-Hexadecane.Pressure is non-uniform Distribution between 74Psi and 400Psi.Mean pressure in freezing n-Hexadecane is approximately 160Psi.Do not wish to be fettered by any particular theory, perhaps pressure distribution heterogeneous is that the anisotropic growth due to n-Hexadecane crystal causes.The bending stiffness of graphite flake only has 9 * 10 ^-11square nanometers, causes under 160Psi mean pressure between graphite flake the variation of resistance over 400 times.

Claims

1. a method of preparing the fluid that comprises particle, provides a kind of fluid that comprises particle, and the freezing formation of fluid is comprised to the polycrystalline solids of grain and grain boundary; Wherein the largest cross-sectional sized of most of particles is 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, at least the part particle in fluid, towards the zone migration of crystal boundary, is formed on the granule density of grain boundaries higher than inner at crystal grain.

2. the process of claim 1 wherein in freezing suspension medium, particle forms a network.

3. the method for claim 2, particle forms an interconnective network.

4. the particle the process of claim 1 wherein comprises that those specific conductivity and/or thermal conductivities at least are in one direction at least fluid conductivity and/or 5 times of above materials of thermal conductivity.

5. the process of claim 1 wherein that particle comprises nanotube, nanometer disk, nano flake, nano wire or nanometer filament.

6. the process of claim 1 wherein that particle comprises carbon back particle.

7. the process of claim 1 wherein that particle comprises graphite flake, carbon nanotube, carbon nano wire or carbon nanometer filament.

8. the process of claim 1 wherein that particle comprises metal.

9. the process of claim 1 wherein that particle comprises metal nanometer line, metal nano fiber, metal nano dish, metal nano plate or metal nanoparticle.

10. the process of claim 1 wherein that particle comprises metal oxide.

11. the process of claim 1 wherein that the flakiness ratio of most of particles is at least 3:1.

12. the process of claim 1 wherein that fluid comprises water.

13. the process of claim 1 wherein that fluid comprises organic solvent.

14. the process of claim 1 wherein that fluid comprises alcohol.

15. the process of claim 1 wherein that fluid comprises hydrocarbon polymer.

16. the process of claim 1 wherein that fluid comprises n-Hexadecane, eicosane, triacontane, dodecane, ten alkane, undecane, octadecane or pentadecane.

The method of 17. claims 1, fluid comprises hydrogel.

The method of 18. claims 1, fluid comprises metal.

19. 1 kinds of methods of preparing the fluid that comprises particle, provide and have comprised the suspension medium of first-phase and the particle in suspension medium; Wherein the largest cross-sectional sized of most of particles is 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; At suspension two ends, apply thermal gradient and/or electromotive force and allow suspension medium generation first-phase to the phase transformation of second-phase, make thus the thermal conductivity of suspension and/or specific conductivity change.

The method of 20. claims 19, wherein suspension is a part for thermistor.

The method of 21. claims 19, wherein suspension is a part for temperature sensor.

The method of 22. claims 19, wherein suspension is a part for electrical fuses.

The method of 23. claims 19, wherein phase transformation is that resistive heating by suspension causes.

The method of 24. claims 19, wherein the thermal conductivity of phase transformation rear suspension liquid at least changes twice.

The method of 25. claims 19, wherein the specific conductivity of phase transformation rear suspension liquid at least changes 10 times.

The method of 26. claims 19, suspension at least bears 2 freeze/thaw cycles.

The method of 27. claims 19, wherein the variation between first-phase and second-phase is not less than 20% at all after dates of 5 freeze/thaw for thermal conductivity and/or specific conductivity.

The method of 28. claims 19, wherein the composition of suspension medium has at least fusing point and/or the freezing point of part based on composition to select.

The method of 29. claims 19, wherein the fusing point of the composition of suspension medium and/or freezing point are between-120 ℃ and 200 ℃.

The method of 30. claims 19, wherein suspended substance comprises liquid phase suspension, and phase transformation comprises and freezing.

The method of 31. claims 19, wherein suspended substance comprises solid composite material, phase transformation comprises thawing.