EP2339184A2

EP2339184A2 - Fluid transfer apparatus

Info

Publication number: EP2339184A2
Application number: EP09814824A
Authority: EP
Inventors: Sae Chae Jeoung; Tae Oh Yun; Hyun Joo Shin; Suk-I Woo; Yeon-Yl Park
Original assignee: Korea Research Institute of Standards and Science KRISS
Current assignee: Korea Research Institute of Standards and Science KRISS
Priority date: 2008-09-22
Filing date: 2009-09-22
Publication date: 2011-06-29
Also published as: JP2012503137A; WO2010033008A3; US20110171043A1; WO2010033008A2; KR20100033732A; KR101603489B1; JP5610544B2

Abstract

The invention relates to an apparatus for transferring a fluid, an object to be transferred, in the vertical or horizontal direction. More particularly, the apparatus of the present invention has a surface formed into a pattern recursively alternating in a fluid transfer direction such that the surface of the apparatus has a contact angle different from that of the fluid, and the fluid is transferred by the hydrodynamic force generated by the difference of the contact angles. The fluid transfer apparatus of the present invention, more particularly, a microfluidic tube for fluid transfer, minimizes the consumption of energy of external sources including an external device, physical vibration from wind power, force from an electromagnetic field generated by static electricity or an electric field, physical force, vibration from thermal energy, or the like, and enables the fluid to be transferred in the vertical or horizontal direction without using a pump.

Description

[Technical Field]

The present invention relates to an apparatus for vertically or horizontally transferring a fluid, which is a liquid to be transferred, and more particularly, to an apparatus having a novel structure, which can minimize energy consumption and control the direction in which the fluid is transferred.

[Background Art]

Requirements for technology and apparatus that can transfer water and various types of liquid and control the transfer thereof are proposed in various forms. Recently, energy and environmental issues have become increasingly important due to high oil prices and environmental problems, therefore the development of fluid transfer technology, which is applicable to various fields, consumes less energy, and is environmentally friendly, is required.
Studies on the surface preforming of solids associated with the transfer and transportation of liquid have been actively conducted over the past fifty years. In particular, methods of reforming various physical/chemical properties of the surface of an apparatus in order to impart a predetermined inclination to the physical properties that participate in the flow of water have been developed.
For example, in surface reforming technologies, research and development for reforming the surface properties by controlling the degree of processes, such as grafting-from polymerization, plasma processing, and corona discharge, which are well-known, have been conducted. For this, various bottom-up and top-down lithographic and nonlithographic methods have been already developed. However, these methods have encountered limitations in that they are generally only applicable within a short distance (J. Genzer et al, "Surface-Bound Soft Matter Gradients," Langmuir, 24, 2294-2317, 2008.
As a totally different method from the control of the flow of water through the surface reforming as described above, research was undertaken on the control of the motion of water by physically analyzing the motion of water droplets on a heating plate in 2006 (H. Linke et al, "Self-Propelled Leidenfrost Droplet," Phys. Rev. Lett., 96, 154502-1-154502-4, (2006)). However, this method consumes a great deal of energy.
In the meantime, the existing trend for the development of technology conceived from the transfer of water through the vascular tissues of the plant is generally used for environmental applications, such as the removal of heavy metals.
Such research is generally carried out in relation to molecular biology, with the aim of increasing efficiency and optimizing the effects by reforming the character of the plant.
With regard to the development fields of the technology conceived from the transfer of water through the vascular tissues of the plant, at present, major studies are underway on the speed of transferring water depending on changes in the composition and surrounding environment, including the types and concentrations of ions in the soil and water surrounding the roots. Investigation of genes, which participate in the biosynthesis of the components of the vascular tissues, such as cellulose, hemicellulose, and lignin, as well as functional genetic studies on the structural changes triggered by mutation, is being conducted using Arabidopsis thaliana, an annual weed, as a model plant. However, no major studies have been carried out on the influence of the transfer of water. In addition, neither monocotyledon nor woody plants have been studied.

[Disclosure]

[Technical Problem]

An object of the present invention is to provide an apparatus for vertically or horizontally transferring a fluid, which is a liquid to be transferred.
More particularly, the present invention provides an environmentally friendly fluid transfer apparatus that can transfer a fluid while consuming minimum energy, and provides a fluid transfer apparatus that can perform a very efficient heat exchange with the outside and ensure that any damage to the system of fluid transfer and the apparatus by external physical impacts or mechanical influences such as bending is minimized.

[Technical Solution]

In an aspect, the present invention provides an apparatus for transferring a fluid, an object to be transferred, the apparatus including a surface having surface sections formed into a pattern recursively alternating in a fluid transfer direction such that the surface sections have different contact angles with the fluid, wherein the fluid transport is controlled by the hydrodynamic force generated by the difference of the contact angles.
In an embodiment, the surface sections having different contact angles with the fluid have a fluid sliding angle ranging between preferably, 0° and 5°, practically 0.1° and 5°.
In an embodiment, the difference between the contact angles that the surface sections have ranges between preferably 3° and 180°.
In an embodiment, the surface is formed with repeated pattern having a toothed form with continuously increased contact angle on the tooth surface.
In an embodiment, the surface is an inner surface of a tube, which includes closed type surface bands which are connected at opposite ends or helical surface sections recursively alternating with each other, wherein the bands or the helical surface sections respectively have different contact angles with the fluid.
In an embodiment, a step is formed between the bands or the surface sections having different contact angles, wherein the surface section having a high contact angle with the fluid has a curvature to protrude.
In an embodiment, the tube has a diameter ranging between 100µm and 2000µm, preferably, and the width of the band or helical surface section has a range 0.0001 to 5 times the diameter of the tube.
In an embodiment, the width of the surface section having a high contact angle with the fluid is smaller than that of the surface section having a low contact angle with the fluid.
In an embodiment, the center line of the helical surface section in the widthwise direction intersects the lengthwise direction of the tube at an angle ranging between 20° and 70°.
In an embodiment, the step has a range 0.0001 to 0.01 times the diameter of the tube.
In an embodiment, the fluid to be transferred by the fluid transfer apparatus is water. Here, the surface having a different contact angle with the fluid includes a hydrophobic surface and a super-hydrophobic surface.
In an embodiment, the hydrophobic surface and the super-hydrophobic surface respectively are a polymer surface, wherein the super-hydrophobic surface is formed by irradiating ultrafast laser beams onto the hydrophobic surface.
In an embodiment, the hydrophobic surface is a poly(dimethylsiloxane) (PDMS) surface.

[Advantageous Effects]

The fluid transfer apparatus of the invention has advantages in that it can vertically or horizontally transfer a fluid using minimum amount of energy, such as the wind present in nature or artificial vibration, and control the direction in which the fluid is transferred.
The closed fluid transfer apparatus performs a very effective energy exchange with an external device, since it has a very precise tubular shape. This fluid transfer apparatus can minimize damage caused by external physical impacts or mechanical influences such as bending, be fabricated using a variety of materials including almost all types of high molecular material, metal, and nonmetal, and be used in various fields, such as a fluid transfer system for a multistory building; a ultra-power-saving silent cooler, which does not need a cooling motor; a biochip, which does not need a fluid pump; and a microfluidics chip.

[Description of Drawings]

FIG. 1 is an example view showing (only) the surfaces of an open or closed fluid transfer apparatus according to the invention, the surfaces being in contact with a fluid, which is a liquid to be transferred;
FIG. 2 is a conceptual view showing the cross section of a droplet having different contact angles;
FIG. 3 is a scanning electron microscope photograph that precisely observes a structure of a xylem of a lily stem;
FIG. 4 is a cross-sectional view showing an embodiment of an open type fluid transfer apparatus according to the present invention;
FIG. 5 is a perspective view showing an embodiment of an open type fluid transfer apparatus according to the present invention;
FIG. 6 is a view showing an example of a closed type fluid transfer apparatus according to the present invention;
FIG. 7 is a view showing another example of a closed type fluid transfer apparatus according to the present invention;
FIG. 8 is a view showing still another example of a closed type fluid transfer apparatus according to the present invention;
FIG. 9 is a view showing a further example of a closed type fluid transfer apparatus according to the present invention;
FIG. 10 is a view showing a further example of a closed type fluid transfer apparatus according to the present invention;
FIG. 11 is a view showing an exemplary application of the fluid transfer apparatus of the invention;
FIG. 12 is an optical photograph showing a mold of an open type fluid transfer apparatus and a PDMS substrate, which are manufactured according to the present invention;
FIG. 13 is a graph showing variation in a contact angle and a sliding angle, which is induced by the control of the fluence of the ultrafast laser; and
FIG. 14 is a view showing sequential still images of a droplet flowing through an open type fluid transfer apparatus which is manufactured according to the present invention.

*Description of Reference Numerals of Major Parts in the Drawings*

100: Droplet 210: High Contact Angle Surface
220: Low Contact Angle Surface 230: Toothed Surface
231: Surface having High Contact Angle in the Toothed Surface
232: Surface having Low Contact Angle in the Toothed Surface
233: Surface having Largest Contact Angle
200: Tube

[Mode for Invention]

Hereinafter, the fluid transfer apparatus of the present invention will now be described in greater detail with reference to the accompanying drawings. The figures, which will be presented later, are provided by way of example, with which a person having ordinary skill in the art can fully understand the principle of the invention. Therefore, the present invention is not limited to the following figures but can be embodied in other forms. Throughout the specification, the same reference numerals designate the same components, and some parts of the figures may be exaggerated in order to clarify the structure.
It is intended, however, that unless otherwise defined, the technical and scientific terminologies used herein may be understood by a person having ordinary skill in the art. In the following description of the present invention, detailed descriptions of known functions and components incorporated in the following description and the accompanying drawings will be omitted when it may make the subject matter of the present invention unclear.
The fluid transfer apparatus of the invention is an open type fluid transfer apparatus, in which at least two ends and at least one side surface are open, or a closed type fluid transfer apparatus, in which only two ends are open. The open type fluid transfer apparatus includes a plate that is macroscopically planar, a plate that has a macroscopic curvature, and polygonal, elliptical, and circular tubes, each of which has at least one open edge. The closed type fluid transfer apparatus, in which only two ends are open, includes polygonal, elliptical, and circular tubes. Here, the closed type fluid transfer apparatus is characterized by being a micro tube.
The fluid transfer apparatus of the invention is the above-described closed or open type fluid transfer apparatus, which specifies the surface that is in contact with a fluid so that it transfers the fluid by being supplied with minimum energy.
FIG. 1 is an example showing (only) the surfaces of the open or closed type fluid transfer apparatus of the invention, which are in contact with a fluid, which is a liquid to be transferred. The surfaces include surfaces 210 and 220, which define different contact angles with the fluid. The surfaces 210 and 220 are alternately and repeatedly formed in the direction in which the fluid is transferred (passage in the direction of an artificial fluid flow). The fluid is transferred by a hydrodynamic force, which is created by the difference between the contact angles.
More specifically, as shown in FIG. 2, the surface 210 that has a high contact angle with the fluid 100 to be transferred and the surface 220 that has a relatively low contact angle are continuously alternated and repeated. The fluid to be transferred, particularly, liquid droplets to be transferred, which are discontinuously transferred in the form of multiple liquid droplets, experience interfacial tension equilibrium made by three interfacial energies, including solid-liquid interfacial energy, solid-vapor interfacial energy, and liquid-vapor interfacial energy, at positions A and B, in which three phases are in contact. The fluid has a high contact angle θ1 on the surface 210, in which the solid-liquid interface energy is similar to the solid-vapor interfacial energy, and a relatively low contact angle θ2 on the surface 220, in which the solid-liquid interfacial energy is lower than the solid-vapor interfacial energy.
When the different contact angles θ1 and θ2 shown in FIG. 2 are formed inside a single liquid droplet 100, a force that is generated by the difference Δθ=θ1-θ2 between the contact angles transfers the liquid droplet 100 from the surface 210 having a high contact angle to the surface 220 having a low contact angle.
The above-mentioned fluid transfer mechanism of the invention is based on a new water transfer mechanism that was discovered by precisely investigating and analyzing the xylem of the plant.
FIG. 3 is a photograph that precisely observes a structure of xylem of a lily stem, in which FIG. 3(a) is a scanning electron microscope photograph in which the lily stem is cut parallel to a xylem direction. As can be seen from FIG. 3(a), a microstructure having a diameter of a few microns is present in xylem in a helical or double helical shape, and its surface is covered with lignins.
Further, micro rings that are inclined at an angle of about 60° to a proceeding direction of the xylem have been observed at an inner wall of xylem depending on the kind of plants.
FIG. 3(b) is a scanning electron microscope photograph in which a surface of the microstructure of this xylem is observed at a higher magnification. It can be found that lignins are randomly distributed on the surface of the microstructure with a size of a few tens to a few hundreds of nanometers. An effect which this micro-nano hybrid structure has on rheological properties is known as a so-called lotus effect, and a surface of the hybrid structure has the property of superhydrophobicity (or super-water-repellency).
Meanwhile, it can be found that, when these micro-sized helices are distributed on the surface, the surface of xylem between the helices has no microstructure, but is covered with the lignins for the considerable part. Thus, this part has the property of water-repellent surface at a considerable level due to the hydrophobic lignins.
The application of the present invention has discovered from this result that the surface of xylem has a regular repetitive rheological variation of the microstructure having super-water-repellency at the portion where the microhelices are present and the water repellency of the surfaces between the microhelices, and water is transferred in the xylem of the plant by a rheological force caused by this water-repellent difference.
The present invention is based on this discovery, and thus provides an apparatus in which a plane having a different contact angle with the fluid is alternated in a transferring direction of the fluid (an artificial flow direction of fluid) and is repetitively formed on a surface of the apparatus that contacts the fluid to provide a movement passage of the fluid, thereby dissipating minimum external energy to allow fluid to be transferred in vertical and horizontal directions.
When a droplet 100 moves due to a force caused by a difference in the aforementioned contact angle, the difference between the contact angles, a length of the surface having one contact angle in a movement direction of the fluid, an interval between the surfaces having different contact angles on the basis of the fluid movement direction, etc. must be basically decided according to a size of the droplet.
Preferably, the droplet must have a volume that can be transferred in a vertical and horizontal direction by a force caused by the difference of the contact angle regardless of gravity. Here, the density of the droplet must also be considered.
It is known that, when the droplet has a volume of about 3 to 4 µl, it can offset the influence of the gravity by the buoyancy pressure in air and the adhesion force of water itself. When a diameter of the tubular transfer device according to an embodiment of the present becomes large to have a gravitational effect, an influence of gradient force of a wall can be offset by the gravity. As such, the volume of the droplet is preferably less than 0.004 µm³ and more preferably from 1 nm³ to 0.004 µm³.
Preferably, to effectively transfer the droplet, the contact angle difference (Δθ=θ1-θ2) of the surface having different contact angles ranges from 3° to 180°. To prevent transfer efficiency from being reduced by resistance (drag force) when the fluid comes into contact with the surface, a sliding angle of the fluid preferably ranges from 0° to 5° on all the surfaces contacting the fluid to be transferred.
FIG. 4 is a cross-sectional view showing an open type fluid transfer apparatus according to an embodiment of the present invention in which a plate has a toothed surface.
The tooth 230 (surface forming a ridge) of the plate is characterized in that a contact angle is continuously reduced from one surface 231 having a relatively high contact angle to one surface 232 having a relatively low contact angle.
The contact angle is continuously reduced on the tooth 230 as in FIG. 4, so that the droplet 100 can be smoothly and continuously transferred. The droplet 100 is transferred from one surface 231 of the toothed surface having the high contact angle to an end of one surface 232 having the low contact angle, and then is transferred to an edge by physical vibration caused by inertia, an external device, a wind force, etc., by vibration caused by an electromagnetic force generated by static electricity or an electric field, a physical force, and thermal energy.
Here, the droplet transferred to the end of one surface 232 having the low contact angle has a probability of moving toward one surface 231 having a high contact angle or the edge again. The droplet moving toward one surface 231 having a high contact angle is again transferred to the end of one surface 232 having a low contact angle by a force caused by the aforementioned contact angle difference, so that all the droplets 100 are transferred in a single direction D.
FIG. 5 is a perspective view showing an open type fluid transfer apparatus according to an embodiment of the present invention. In a plate 200 having a toothed surface, a surface 230 where a contact angle is continuously reduced from one surface 231 having a high contact angle to one surface 232 having a relatively low contact angle is formed on a predetermined area rather than an entire area of the toothed surface of the plate 200 in a direction intended to transfer fluid, and thereby a specific channel can be formed on the plate surface. Here, as shown in FIG. 5, a surface 233 having the largest contact angle is formed on a lateral surface of the channel which is not a planed transfer direction of the droplets. Thus, it is preferable to previously prevent the droplet from departing from the channel.
The open type fluid transfer apparatus as shown in FIGS. 4 and 5, a maximum difference of the contact angle continuously varying at one tooth 230, a length L of the tooth 230, an inclined angle γ of the tooth 230, etc. must be decided according to a size of the droplet to be transferred.
In detail, the maximum difference of the continuously varying contact angle (the contact angle of the surface 231 minus the contact angle of the surface 232) may range from 3° to 180°. The length L of the tooth 230 may range from 100 to 5000 µm, and the angle γ may range from 7° to 90°.
FIGS. 6 through 10 show an example of a closed type fluid transfer apparatus according to an embodiment of the present invention, and more particularly a cylindrical micro tube. FIG. 9 shows the case where convexity and concavity are not formed on an inner surface of the tube, and FIGS. 6, 8, 9 and 10 show the case where convexity and concavity are formed on an inner surface of the tube. Particularly, an example where a surface having a high contact angle with the fluid to be transferred protrudes with a curvature (FIGS. 8 through 10) is shown, and an example where a tooth 230 similar to FIG. 4 is formed is shown (FIG. 6). In both cases, a fluid transfer direction is set from a lower portion to an upper portion of the tube.
At this time, a material of the tube 200 may be metal, ceramic, polymer, or glass without considering a contact angle with respect to fluid. In the case where convexity and concavity are present, the convexity and concavity formed in the inner surface of the tube are also formed of the same material as the tube. A surface 230 where a contact angle is continuously reduced from one surface 231 having a high contact angle, or one surface 210 having a high contact angle and one surface 220 having a low contact angle may be provided only on the inner surface of the tube using coating, deposition, surface modification, etc.
At this time, a material of the tube 200 may be metal, ceramic, polymer, or glass having a low contact angle with respect to fluid to be transferred. In the case where convexity and concavity are present, the convexity and concavity formed in the inner surface of the tube may also be formed of the same material as the tube. A surface 230 where a contact angle continuously increases or one surface 210 having a high contact angle may be provided using surface modification.
At this time, a material of the tube 200 may be metal, ceramic, polymer, or glass having a high contact angle with respect to fluid to be transferred. In the case where convexity and concavity are present, the convexity and concavity formed in the inner surface of the tube may also be formed of the same material as the tube. A surface 230 where a contact angle is continuously reduced or one surface 220 having a low contact angle may be provided using surface modification.
A diameter, particularly an inner diameter d, of the tube shown in FIGS. 6 through 10 decides a size of the droplet to be transferred. To discontinuously transfer a plurality of droplets having a volume of 0 to 0.004 µm³, the inner diameter d of the tube may range from 100 µm to 2000 µm.
In the case where the inner surface of the tube is a toothed surface as in FIG. 6, one tooth of the toothed surface is formed from one surface (lower position) having a high contact angle to one surface (upper position) having a low contact angle as described with reference to FIG. 4. A maximum difference of the contact angle continuously varying at one tooth may range from 3° to 180°. A length L of the tooth 230 may range from 100 to 5000 µm, and an angle γ between the tooth and the fluid transfer direction (direction of a major axis of the tube) may range from 7° to 90°.
FIG. 7 shows another example of a closed type fluid transfer apparatus having an even inner surface in which a high contact angle surface 210 with a droplet and a low contact angle surface 220 with a droplet are at both respective ends connected with each other, each surface forming a closed band 210 and 230, wherein the center line of the closed band 210 and 230 in the widthwise direction intersects the fluid transfer direction (the lengthwise direction of a tube) at 90°.
However, FIG. 7 shows only an example where an inner surface of a tube is formed such that a high contact angle surface and a low contact angle surface recursively alternate with each other in the fluid transfer direction, so that the center lines of the bands 210 and 230 in the widthwise direction intersect the fluid transfer direction (the lengthwise direction of the tube) at 90° or less.
Further, unlike the closed bands shown in FIG. 7, the inner surface of the tube may be a surface in which helical band surfaces having different contact angles recursively alternate.
Now a description will be made of an embodiment of a closed type fluid transfer apparatus that has an irregular inner surface of a tube, with reference to FIGS. 8 through 10. However, even though a closed type fluid transfer apparatus has an even inner surface of a tube, it also has a similar characteristic of fluid transfer to that of the closed type fluid transfer apparatus of this embodiment.
FIGS. 8 through 10 show examples of the closed type fluid transfer apparatus having an even inner surface in which a curved protrusion has a high contact surface with a fluid to be transferred.
As shown in FIG. 8(a), the inner surface has a high contact surface 210 with the fluid and a low contact surface 220 with the fluid, which alternate with each other, each surface forming a band (including a band portion curved by the protrusion) in which both respective ends of the surfaces having different contact angles are connected with each other, and wherein the center lines of the bands in the widthwise direction intersect the fluid transfer direction (the lengthwise direction of a tube) at 90°.
FIG. 8(b) is a perspective view showing only the inner surface of the tube, a section of which is illustrated in FIG. 8(a), wherein respective widths t1 and t2 of the high contact angle surface 210 and the low contact angle surface 220 have a dimension 0.0001 through 5 times, preferably, a diameter d of a tube.
More preferably, the width t2 of the high contact angle surface 210 is smaller than that of the high contact angle surface 210. While the surfaces 210 and 220 having different contact angles alternate, the surfaces having the same contact angle may of course have different widths.
It is preferred that the protrusion of the high contact angle surface 210 have a curvature that changes continuously and smoothly and that the protrusion have both negative and positive curvatures relative to a center axis of the tube.
The height h of the protrusion may preferably be 0.0001 through 0.01 times the diameter d of the tube.
FIG. 9 shows an example of a closed type fluid transfer apparatus in which center line of a band in the widthwise direction intersects the fluid transfer direction (the lengthwise direction of a tube) at a certain angle. Here, widths t1 and t2 of a high contact angle surface 210 and a low contact angle surface 220 mean the smallest widths, respectively. The tube is made of a material having a low contact angle, and the high contact angle surface is provided by surface modification of the tube material.
The angle (α) defined by the center line of the band in the widthwise direction and the fluid transfer direction (the lengthwise direction of the tube) may preferably range from 20° to 70°.
FIG. 10 shows an example of a closed type fluid transfer apparatus in which an inner surface of a tube is formed by helical type bands, which are not the closed type, alternating with each other, wherein the inner surface is formed by a band of a high contact angle surface 210 and a band of a low contact angle surface 220.
While FIG. 10 has illustrated that the high contact angle surface 210 has a single helical structure, the high contact angle surface 210 may of course have a multi-type helical structure, a width of which is identical or different.
The center line of the helical band in the widthwise direction intersects the fluid transfer direction (the lengthwise direction of the tube) at an angle ranging from 20° to 70°, preferably.
In the context of both the additional reduction in the contact resistance according to a micro nanostructure (surface irregularity) and continuous force-provision for droplet transfer, among examples of FIGS. 7 through 10, the closed type fluid transfer apparatus of the invention preferably has a similar structure to the helical structure of the example of FIG. 10.
FIG. 11 shows an exemplary application of the fluid transfer apparatus of the invention as a transfer unit that consists of the plurality of fluid transfer apparatuses of FIG. 10 to transfer fluids in the vertical direction.
A fluid, an object to be transferred by the above-mentioned fluid transfer apparatuses is water, particularly. Here, the surfaces 210 and 220 that have different contact angles with the fluid respectively are a hydrophobic surface and a super-hydrophobic surface, particularly.
A contact angle of the super-hydrophobic surface (with a water droplet) is larger than that (with a water droplet) of the hydrophobic surface, wherein the contact angle of the hydrophobic surface preferably ranges between 80° and 120°, and the contact angle of the super-hydrophobic surface preferably ranges between 90° and 180°.
The hydrophobic and super-hydrophobic surfaces respectively are a polymer surface, particularly. The super-hydrophobic surface is characteristically formed by irradiating the hydrophobic surface with an ultrafast laser beam. Here, the hydrophobic surface is a poly(dimethylsiloxane) (hereinafter referred to as 'PDMS') surface, particularly.
The surface modification using an ultrafast laser according to the present invention is characteristically carried out by irradiating an ultrafast laser onto a polymer substrate or an inner surface of a polymer tube, including PDMS, so as to form thereon a nano-size microstructure with a few to hundreds nanometers or less, thereby forming a super-hydrophobic surface.
Here, the ultrafast laser preferably has a pulse of femto sec., a wavelength of 700 to 1000 nm, a pulse width of 100 to 200 fs, spacing of 3 to 5 µm between laser beam spots, and the spot size on the substrate of 6 to 9 µm. Further, preferably, upon irradiation of the ultrafast laser, the feed rate of the substrate is 3 to 5 mm/sec, and chromatic aberration (N.A) of an objective lens for adjusting a focal point of a femto-sec laser beam is 0.1 to 0.2. Further, preferably, the fluence of the ultrafast laser is 2 to 8 J/cm², the average number of pulses irradiated onto the substrate surface is 1.5 to 2.5. Here, the fluence of the ultrafast laser for surface modification to obtain the contact angle of 90° to 180° characteristically ranges from 2 J/cm² to 8 J/cm², and that to obtain a sliding angle of 5 ° characteristically ranges from 4J/cm² to 8 J/cm².
In order to experimentally prove excellence of the present invention, an open type fluid transfer apparatus having a similar structure to that of FIG. 3 was manufactured by surface modification using polydimethylsiloxane and laser beams.
First, as shown in FIG. 12(a), a stainless metal plate was manufactured to provide a stainless mold surface having a section similar to that of FIG. 3. Next, the mold surface was washed and applied with a mixed solution, which is obtained by mixing prepolymer of PDMS with an initiator in a ratio of 10:1 and stirring it, to polymerize the same, thereby forming a PDMS substrate of a fluid transfer apparatus as shown in FIG. 12(b). Here, the manufactured PDMS substrate has a toothed surface with tooth faces, each having a length (L) of 5.0 mm, and a slope angle (γ) of 12°.
Next, the toothed surface of the PDMS substrate was partially irradiated with an ultrafast laser to fine process it, thereby modifying the rheological property of the toothed surface.
In the irradiation step, the surface of the PDMS substrate was irradiated with laser having a wavelength of 810 nm and a pulse width of 150 fs, using a laser device (from Quantronix, USA). Here, the PDMS substrate was held on an XY-stage and moved at a feed rate of 4 mm/sec in an x-axis. In this case, considering the feed rate and the repetition speed of the laser, the spacing between respective laser spots is 4µm. Further, the PDMS substrate was exposed at a fixed focal point to femto-sec laser beams through an objective lens (N.A=0.14) which was held on another stage linearly-movable in a z-axis. Here, considering optical characteristics of the objective lens, the laser spot size on the surface of the PDMS substrate is 7.7 µm. Thus, the average number of laser pulses irradiated onto the surface of the PDMS substrate was restricted to approximately 1.9, thereby minimizing the effect of accumulated heat possibly occurring due to repetitive irradiation of the ultrafast laser with time intervals of 1 ms (1 kHz).
It could be seen that in the case of the PDMS substrate directly surface-modified using the femto-sec laser, a contact angle is 165° and a sliding angle is 3° or less, so that it belongs to Cassie-Boxter (C-B) model.
More particularly, a super-hydrophobic DPMS substrate was fabricated by the irradiation of an ultrafast laser with proper intensity of fluence, and the microstructure of the surface of the PDMS substrate that was surface-treated was formed so that a hyperfine structure of nano size is arranged on the microstructure of micro size, forming a very rough surface, which was found as being the same as the microstructure of the super-hydrophobic surface that is discovered in nature.
FIG. 13 is a graph showing variation in a contact angle and a sliding angle, which is induced by the control of the fluence of the ultrafast laser. It could be seen that the contact angle of 90° to 170° is obtained under the fluence ranging from 2 J/cm² to 8 J/cm², and the sliding angle of 3° or less is obtained under the fluence ranging from 4J/cm² to 8 J/cm².
FIG. 14 shows sequential still images of a droplet flowing through an open type fluid transfer apparatus that is similar to that of FIG. 3 fabricated by using the PDMS substrate and the irradiation of the ultrafast femto-sec laser, where still images are obtained from a moving picture picking up the droplet flow. From FIG. 14, it could be seen that the droplet rolls very fast from the region (
) (super-hydrophobic region) to the last region (
) (hydrophobic region of the PDMS substrate itself) (near edge) of the toothed surface through the remaining intermediate region which was surface-modified.
In the meantime, like the above open type fluid transfer apparatus, the closed type fluid transfer apparatus can be micro-structured as follows. The PDMS substrate is fabricated so that the width is made thinner and the surface is irregular in which micro features (protrusions) are formed inclined, at a certain angle, against a direction of water flow. Here, the angle defined between the micro feature and the water flow can be precisely estimated and designed by taking a relation with a diameter of a micro fluid tube into consideration when designing the device. Then, the fabricated PDMS substrate is subjected to the above-mentioned laser irradiation or another existing method to change rheological property, and then is formed into a tube, thereby providing a closed type micro fluid tube of the invention.
The fields of the surface structure and function of fluid transfer, which were proposed by the present invention, are very advanced and highly novel fields in view of understanding the principle thereof. Thus, through the present invention, it is possible to analyze the relation between the microstructure of the inner surface of the fluid tube and the rheological property, so that it can be understood that the present invention has highly applicability regarding practical implementation.
Although the present invention has been described with reference to the embodiments and drawings associated with such as specific manufacturing processes or the like, they have been presented for helping one understand general principles of the invention and do not limit the invention, so those skilled in the art will appreciate that various modifications, additions and substitutions are possible from the description.
Therefore, the present invention is not limited to the embodiments described, but includes all of features as disclosed in the accompanying claims, and changes and equivalents thereof.

Claims

An apparatus for transferring a fluid, an object to be transferred, the apparatus comprising a surface having surface sections formed into a pattern recursively alternating in a fluid transfer direction such that the surface sections have different contact angles with the fluid, wherein the fluid transport is controlled by the hydrodynamic force generated by the difference of the contact angles.
The apparatus according to claim 1, wherein the surface sections having different contact angles with the fluid have a fluid sliding angle ranging between 0° and 5°.
The apparatus according to claim 2, wherein the surface is formed with repeated pattern having a toothed form with continuously increased contact angle on the tooth surface.
The apparatus according to claim 2, wherein the surface is an inner surface of a tube, which includes closed type surface bands connected at opposite ends or helical surface sections recursively alternating with each other, wherein the bands or the helical surface sections respectively have different contact angles with the fluid.
The apparatus according to claim 4, wherein a step is formed between the bands or the surface sections having different contact angles.
The apparatus according to claim 5, wherein the surface section having a high contact angle with the fluid has a curvature to protrude.
The apparatus according to any one of claims 4 to 6, wherein the tube has a diameter ranging between 100µm and 2000µm.
The apparatus according to claim 7, wherein the width of the band or helical surface section has a range of 0.0001 to 5 times the diameter of the tube.
The apparatus according to claim 8, wherein the width of the surface section having a high contact angle with the fluid is smaller than that of the surface section having a low contact angle with the fluid.
The apparatus according to claim 7, wherein the center line of the helical surface section in the widthwise direction intersects the lengthwise direction of the tube at an angle ranging between 20° and 70°.
The apparatus according to claim 6, wherein the step has a range of 0.0001 to 0.01 times the diameter of the tube.
The apparatus according to any one of claims 1 through 6 or of claims 8 through 11, wherein the fluid is water.
The apparatus according to claim 12, wherein the surface having different contact angles with the fluid includes a hydrophobic surface and a super-hydrophobic surface.
The apparatus according to claim 13, wherein the hydrophobic surface and the super-hydrophobic surface respectively are a polymer surface.
The apparatus according to claim 14, wherein the superhydrophobic surface is formed by irradiating ultrafast laser beams onto the hydrophobic surface.
The apparatus according to claim 15, wherein the hydrophobic surface is a poly(dimethylsiloxane) (PDMS) surface.