KR100928057B1 - Super water-repellent surface modification method using ultrafast laser - Google Patents

Abstract

The present invention relates to an ultra-fast laser process capable of making nano- and micro-sized microstructures and hybrid surface layers thereof on a substrate such as PDMS while controlling their position and size under micron-sized resolution. By using ultrafast laser irradiation, it has a controllable position and shape pattern on the substrate, and it is a new process technology that has not been known so far that can change the rheological properties of polymer solid surface such as PDMS. Innovatively reduces additional production cost factors, such as building clean processes and expensive process environments such as vacuum deposition equipment, and enables various types of patterning and microprocessing under general laboratory conditions. It is a new technology.

The laser process technology will be a patent that includes the original process technology, which is essential for the development of various devices using polymers in various fields such as electronic, optical, and bio. In particular, the laser process technology has a range of applications in the development of various devices in various fields, such as solving problems arising from the adhesion of liquids such as water on the surface of the shaking plate of electronic, display, optical, bio, and mouth instruments. Can be extended.

 Super Water Repellent, Ultra Fast Laser, Surface Treatment, Rheology, PDMS, Fluence, Single Pulse, Femtosecond

Description

Ultrafast laser surface modification method to generate superhydrophobic surface}

The present invention relates to a superhydrophobic surface modification method using an ultrafast laser for generating a superhydrophobic surface of a polymer substrate using an ultrafast laser.

Interest in rheologically characteristic and extreme surfaces such as super water repellency has long been received in both basic research and applications.

The water-repellent super water-repellent surface not only controls the wetting properties of microarray devices, such as micro- and nano-sized biologically quantitative approaches, but also protects microelectronic devices from adverse effects from ambient water or moisture. It is also used for surface treatment to control cell growth and for self-cleaning of surfaces such as windows and walls exposed to the outside.

Super water-repellent surfaces have already been used in various ways by evolution in nature, especially on insect wings, eyes, and the legs and legs of water striders that live in leafy plants such as lotus and mosquitoes. . In particular, super water-repellent properties with high contact angle (usually 150 ° or more), which means the angle of tangential direction of water droplets on the surface, and very small sliding angle, which means the minimum tilt at which water droplets on the surface begin to roll. The demand for surface generation is increasing.

In general, the method mainly used in the production site to have a super water-repellent has been achieved by applying a chemically hydrophobic polymer such as Teflon to the target solid surface. In particular, a variety of methods such as surface coating and plasma treatment have been attempted to treat mydevice array surfaces which are being actively developed as biomedical devices. These methods have been used in much the same way to treat surfaces of medical devices intended for insertion into the human body, such as stents. However, this chemical surface coating technology has a very short time because the adhesion between the target surface and the coated compound is modified in a short time by the physical external environment such as friction with the surrounding chemical environment and friction. It is causing a problem.

In recent years, micro-nano-shaped surfaces have been fabricated to impart superhydrophobic properties using many different types of polymers, semiconductors, metals, and ceramics, including lithographic and nonlithographic approaches. A method has been devised. Among these methods, super water-repellent PDMS surface can be produced by two-stage replication with the surface of lotus leaf directly as master. The above method mainly uses the lithography technology that has been used in the conventional semiconductor process, and uses a multi-step nano process that uses very complicated and expensive equipment. Therefore, the complexity and cost of production cost and long process time are inevitable.

On the other hand, using a CO ₂ laser by changing the surface properties of PDMS was announced production is possible the second water-repellent surface. Recently, it has been announced that a superhydrophobic silicon surface can be fabricated by irradiating an ultrafast laser to a silicon surface while SF ₆ gas is injected into a vacuum chamber.

Known laser surface processing techniques have the following technical limitations. The CO ₂ laser process not only avoids thermal deformation on the surface of the target material, but also cannot be applied when the size of the process target is several hundred micrometers or less. In addition, it is possible to limit the application of a polymer including a specific vibration mode (vibration mode). Silicon surface treatment technology in an etched chamber with SF ₆ is basically a disadvantage of having to install and maintain an expensive vacuum chamber and another suitable etching compound for surface treatment other than silicon. There was a problem that the development is not easy because the need for research and development.

Therefore, in order to overcome the above disadvantages, the present invention has devised an ultra-fast laser surface process that can achieve new technological advances that can be applied even in the air.

In the superhydrophobic surface modification method using the ultrafast laser of the present invention, the ultrafast laser beam is irradiated on the surface of the polymer substrate to the surface of the polymer substrate including PDMS, and the microstructure of the microstructure of several to hundreds of microns or less is several to several hundred nanometers. It is characterized by modifying the surface of the polymer substrate to have a nano-size microstructure and to have a super water-repellent surface having a contact angle of 90 ° to 170 ° and a sliding angle of 3 ° or less.

In addition, the ultra-fast laser is characterized by having a few ~ hundreds femtosecond pulse.

In addition, the wavelength of the ultra-fast laser beam is 700 ~ 1100 nm, the pulse width is 100 ~ 700 fs, the transfer speed of the substrate is 3 ~ 5 mm / sec, the interval between the laser beam spot is 3 ~ 20 ㎛, The chromatic aberration (NA) of the objective lens for adjusting the focus of the femtosecond laser beam is 0.1 to 0.2, the laser beam spot size of the substrate surface is characterized in that 6 ~ 20 ㎛.

In addition, the fluence of the ultra-fast laser having a contact angle of 90 ° to 170 ° is characterized in that 2 to 8 J / cm ² .

In addition, the fluence of the ultra-fast laser having a sliding angle of 3 ° or less is characterized in that 4 to 8 J / cm ² .

At this time, the number of average laser pulses irradiated to the substrate surface is characterized in that 1.5 ~ 2.5.

In addition, by filling the polymer mold on the surface of the surface-modified substrate with a super water-repellent surface-modified substrate by the above method and replicating the same as the surface of the substrate; b) separating the duplicated mold from the substrate; c) filling the polymer mold on the duplicated surface of the duplicated mold with the separated duplicated mold as a base material and curing the duplicated mold in the same manner as the face of the duplicated mold; d) repeating step c); Characterized in that comprises a.

Super water-repellent surfaces appear in the wings, eyes and legs of leaf insects of natural plants, with high contact angles (usually 150 ° or more) and low sliding angles (usually 3 ° or less). As a nano / micro hybrid type, the technology to physically understand and simulate the natural state that expresses super water repellency and super hydrophilic phenomena is developed and optimized for three-dimensional process to improve surface properties and performance without chemical surface coating process step. The use time can be significantly increased.

Surface machining using a femtosecond laser process has been found to be an optically promising method for making PDMS surfaces superhydrophobic. The moderate intensity laser irradiation is very similar to the nano / micro hybrid form, which mimics the natural lotus leaf. The development of new process technologies for these super water-repellent materials and surfaces has received a lot of attention in the field of application, and the water-repellent super water-repellent surfaces approach the new micro or nano size and control the wetting properties of microdevices that perform biological quantification. It can be used for surface treatment to grow and self-clean as well as to protect microelectronic devices that are not affected by water or moisture. In particular, the technology of the present invention takes advantage of these characteristics, and it is significant because it overcomes the short stability of a method such as compound coating, which has been generally used so far, and develops a source technology for surface treatment technology that can be used for a long time. can do.

The contact angle and the sliding angle of the droplet, which is a rheological property of the substrate surface, are determined by the surface energy and the surface tension of the liquid, which are the physical and chemical properties of the substrate. Since the properties of the liquid cannot be changed, the rheological properties of the surface are determined by the properties of the surface. So far, the rheological properties of the surface can be explained by the chemical properties of the compounds constituting the surface, the roughness of the surface, and the curvature of the microstructures present on the surface.

The Wenzel model presented earlier by Wenzel and the Cassie model presented by Cassie and Baxter are two different models that illustrate the dependence of the contact angle and the slip angle on the surface of the liquid droplets on the surface roughness. The Cassie model explained the increase in contact angle due to the microscopic air pockets caused by the microstructure on the surface under the droplets, while the Wenzel model showed the change in contact angle as the contact surface increased because the rough surface was completely filled with liquid. Explained. While these two different models differ in their assumptions, the fact that micro- and nano-sized microstructures play a very important role in achieving a super water-repellent surface is the same in both models. On the other hand, it should be noted that in the above models, microstructures or nanostructures are not enough to change the rheological properties of the surface. In other words, the micro-nano hybrid microstructure, in which the nanostructures exist simultaneously on the microstructure, is key to the rheological properties.

Considering these theoretical models, it is very important to make new technological advances in designing and realizing new ways to fabricate superhydrophobic surfaces with mixed micro and nanostructures.

The present invention realizes nano and micro hybrid structures by focusing on the surface of the substrate by using the existing ultra-fast laser ultra-fine processing technology and optical method, which has excellent precision, and utilizes the advantages of the ultra-high speed laser process to maximize New expansions for the production of rheologically useful surfaces, such as water repellency, enable high quality ultrafine processes using them.

Ultrafast lasers have been reported to improve the degree of size dispersion of colloidal nanoparticles significantly better than nanosecond lasers by irradiating a laser onto a solid surface already in the liquid phase. In addition, the inventor of the present invention obtained a result that the nanostructure is formed on the microstructure by irradiating the ultrafast laser on the single crystal Ge. Measurements of ultrafast laser ablation of bulk crystalline Ge substrates show two different process thresholds. In particular, the influence of the second threshold has been shown to be very effective in producing nanostructures suspended on irregular Ge microstructures.

The present invention proposes a technique for surface-treating ultrafast lasers having superhydrophobic properties by irradiating ultrafast lasers to polymer surfaces including PDMS. In particular, the microstructure of the treated surface was very similar to that of lotus leaf in nature, and the high contact angle and low slip angle of water droplets were observed. In particular, the PDMS used as an embodiment in the present invention has high optical transparency, such as high transmittance from short wavelength ultraviolet rays to near infrared rays, and has high chemical and thermal stability, and biological determination with high elasticity for nanocasting suitable for mass production. The biocompatibility that makes this possible is well known. In addition, the technology of the present invention can minimize the spatially excellent resolution and thermal mechanical damage to produce a pattern of complex structure directly on the surface of PDMS, such as for inserting the human body such as biomedical devices and stents of various forms using the same It could be extended to the manufacture of medical devices.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments.

FIG. 1 is a flowchart illustrating a process of assigning a superhydrophobic property to a surface of a PDMS substrate through an ultrafast laser surface modification process and a replication process thereof, and FIG. 2 is a diagram of PDMS (ab) directly modified using an ultrafast laser and its negative ( Scanning electron microscopy images of the cd) and positive (ef) replica surfaces, and the optics of water droplets dropped on PDMS (a) and its negative (b) and positive (c) replica surfaces directly surface-modified using an ultrafast laser. 4 (a) and 4 (b) are schematic diagrams illustrating Cassie-Baxter and Wenzel models, which are two different models used to explain rheological properties that are dependent on surface microstructures. , (c) is a schematic diagram for explaining the state of the surface of the negative replica PDMS substrate, Figure 5 shows the change in the contact angle and sliding angle according to the fluence control of the ultrafast laser This is a graph.

FIG. 1 schematically illustrates a process of fabricating a superhydrophobic PDMS surface through a femtosecond laser surface modification process on a solid PDMS piece and a replication process thereof.

In the superhydrophobic surface modification method using the ultrafast laser of the present invention, the ultrafast laser beam is irradiated on the surface of the polymer substrate to the surface of the polymer substrate including PDMS, and the microstructure of the microstructure of several to hundreds of microns or less is several to several hundred nanometers. It is characterized by modifying the surface of the polymer substrate to have a nano-size microstructure and to have a super water-repellent surface having a contact angle of 90 ° to 170 ° and a sliding angle of 3 ° or less. At this time, the ultra-high speed laser has several to several hundred femtosecond pulses, the wavelength of the ultra-high speed laser beam is 700 to 1000 nm, the pulse width is 100 to 200 fs, and the substrate transfer speed is 3 to 5 mm / sec. The distance between the spots is 3 to 5 μm, the chromatic aberration NA of the objective lens for adjusting the focus of the femtosecond laser beam is 0.1 to 0.2, and the size of the laser beam spot on the substrate surface is 6 to 9 μm. In addition, the fluence of the ultra-fast laser is 2 ~ 8 J / cm ² , the number of average laser pulses irradiated to the substrate surface is preferably 1.5 to 2.5. In this case, the fluence of the ultrafast laser having a contact angle of 90 ° to 170 ° is 2 to 8 J / cm ² , and the fluence of the ultrafast laser having a sliding angle of 3 ° or less is 4 to 8 J / cm ² . .

In the present invention, a laser having a wavelength of 810 nm pulse width of 150 fs (Quantronix, USA) was irradiated onto PDMS polymer surface. The solid PDMS plate was prepared by mixing PDMS base / curing agent in a 10: 1 weight ratio, stirring, removing bubbles in a vacuum state, and curing at 25 ° C. for 24 hours. The PDMS plate was mounted on an orthogonal XY-stage and the substrate was moved at a speed of 4 mm / sec in the x-axis direction. The distance between each laser spot is 4 um considering the moving speed and the repetition speed of the laser. . The femtosecond laser beam was focused on the PDMS surface through an objective lens (N.A. (chromatic aberration) = 0.14) mounted on another stage capable of linear movement in the Z-axis. Considering the optical considerations of the objective lens, the laser spot size of the PDMS surface is 7.7 um. Therefore, the average number of laser pulses irradiated on the PDMS surface of each part is limited to about 1.9 times to minimize the accumulated thermal effect that may be generated by repeated irradiation of ultrafast lasers irradiated at 1 ms time (1 kHz) intervals. It was.

After the surface modification process, the master PDMS plate was coated with 1H, 1H, 2H, and 2H-perfluorooctyl- tricholrosilane to minimize the adhesion between the master substrate and the replicated PDMS.

Using a super water-repellent surface-modified substrate as a base material, the polymer mold is filled and cured on the surface of the surface-modified substrate in the same manner as the surface of the substrate, and the duplicated mold is separated from the substrate and then the separated mold is separated into the base material. By filling the polymer mold on the duplicated surface of the duplicated mold and cured to replicate the same as the face of the duplicated mold.

Using the coated substrate as a master, the replica was replicated in the same manner as in the above PDMS substrate fabrication process. A positive replica was obtained by repeatedly replicating the negative replica obtained at the first replication and the second replication. It is known that the size of the microstructure obtained through the above replication is approximately 20 nm.

1H, 1H, 2H, 2H-perfluorooctyl- for 2 hours under vacuum to minimize the effects of chemically modified surfaces on the ultrafast laser process to measure the rheological properties of the surface-modified PDMS. tricholrosilane was coated. All replicated PDMS substrates were also coated to eliminate the effects on the rheological properties of chemical variations. All contact angles were presented as arithmetic mean values of measurements made on five different surfaces using a commercialized dynamic contact angle device.

2 (a) and 2 (b) are electron micrographs measured under two different magnifications of the surface-modified PDMS substrate. The laser fluence used at this time is 3.5 J / cm ² . Figures 2 (a) and (b) are enlarged pictures 5,000 times and 200,000 times, respectively. Ultra-high speed lasers show that three-dimensional PDMS microstructures remain in place without uniform ablation of the PDMS substrate. The size of FIG. 2 (a) is 60 μm in width and 44 μm in length and is an image of a process surface having an area of 2640 μm ² , which shows that the size of the observed microstructure is about several micrometers. At this time, the average size of the generated microstructures and the spacing between the microstructures were 6 μm and 10 μm, respectively. The creation of such a structure shows that the volume-to-surface ratio of the PDMS surface can be significantly increased by the method of the present invention.

Scanning electron micrographs also show that in addition to the microstructures observed previously, grains significantly smaller than micrometers are observed. It can be seen that the nanostructures between 3 nm and about 300 nm in size are formed not only on the above-mentioned three-dimensional microstructure but also in the valley between the microstructures. It is unusual to note that almost all of the nanoparticles produced are circular in shape. Surface measurements using scanning electron microscopy did not confirm the presence of micro balls and cones regularly, which were reported to be observed when the silicon surface was irradiated with an ultrafast laser under an etch gas atmosphere such as SF ₆ or Cl ₂ . In addition, no evidence of the presence of micro-sized micro-pores reported in the records of CO ₂ laser irradiation on PDMS.

2 (c) and 2 (d) are scanning electron micrographs of negative replicas produced by replicating a surface-modified PDMS substrate as a master. It should be noted that the image features a negative copy of the micro and nano-sized micropores on the observed negative replica PDMS surface compared with the PDMS substrate surface modified with a femtosecond laser. On the other hand, the positively replicated PDMS substrate surface replicated relatively well compared to the surface structure of the directly modified PDMS disk (Fig. 2 (e), 2 (f)). From the SEM images of the microstructures of these negative and positive replica surfaces, the PDMS replication method agrees with the known fact that the microstructure size of the replication limit is up to about 20 nm. In other words, it can be seen that the surface rheological properties of the surface modification through the ultrafast laser of the present invention are still effective in mass production through the above replication.

FIG. 3 is an optical micrograph of droplets observed by dropping several microliters of water onto three different PDMS surfaces previously formed, namely directly modified, negative replicated and positive replicated. The values obtained by averaging the contact angles measured at five different surfaces using the tangents formed at the point where the traces of the substrate surface and the droplets meet using the observed images in this manner are shown in Table 1 below.

The average contact angle of positive replicated PDMS is 150.4˚, direct surface modified PDMS is 165.6˚ and negative replica PDMS is 136.4˚. For reference, the measured contact angle at the intact PDMS surface is 107.1 °. Therefore, by direct modification, the contact angle on the PDMS surface was 165.6˚, the negative replica increased the contact angle to about 136.4˚, and the positive replica increased the contact angle to about 150.4˚. It can be seen that the measured contact angle is larger than 150 °, which is generally the contact angle with water droplets shown in super water repellency.

Super water-repellent surfaces, on the other hand, are known to show very small sliding angles as well as large contact angles of more than 150 °. In the case of PDMS surface subjected to direct surface modification process by laser and its positive replica PDMS surface, water droplets rolled up very quickly even with slight tilting, whereas in vertically negative surface But even if turned upside down, the water droplets did not roll or fall. Quantitatively measured slip angles are shown in Table 1. The comprehensive results of the measured contact and sliding angles indicate that the surface modified PDMS and positive replica PDMS surfaces exhibit typical characteristics of super water-repellent surfaces such as contact angles greater than 150 ° and very small slip angles. . These results clearly show that the technical progress on the effectiveness and mass productivity of the ultrafast laser surface development process technology of the present invention has been achieved.

Consideration of the microstructure of the surface of the superhydrophobic PDMS fabricated based on the present invention is very important in terms of expanding the applicability of the present technology in the future. In particular, it is a significant technological progress to develop a process technology capable of artificially producing the microstructure adopted through long evolution in nature. Therefore, the result of this study is as follows. Superhydrophobic phenomena of the lotus leaf surface observed in nature are known to be due to the presence of nano and micro structures present on the leaf surface. It is known that the average size of the micro-projections is about 6μm and the distance between the protrusions is about 10μm. Nano-sized structures can also be found on or between these micro-sized protrusions. It can be seen that the microstructure shape, size and distribution are surprisingly similar to the surface of the PDMS substrate and the positive replica PDMS fabricated by the method of the present invention. As shown in many previous studies, the rugged structure is a decisive factor in the superhydrophobicity of the lotus leaf. It is known that both lotus leaf and its positive replica have a contact angle of 160 ° and a cloud angle of 2 °. As shown in (a) of FIG. 2, the average size of the protrusion structure of the PDMS irradiated with a laser is 6 μm and the distance between the protrusions is about 10 μm. On the other hand, the valley between the projections and the projections of the PDMS surface irradiated with femtosecond laser is covered with hemispherical nanostructures rather than fabric-shaped nanostructures. Contact angles of droplets on PDMS substrates irradiated with ultrafast lasers are more than 160 ° and hysteresis of contact angles is small. Ultrafast laser beams were used to identify the shape of micro-sized protrusions and hemispherical nanostructures on the surface of PDMS fabricated in such a way that it was sufficiently possible to create superhydrophobic surfaces of artificial polymers. In particular, the PDMS surface processed by the same method is very similar to the surface form of natural lotus leaf as well as hydrophobic.

So far, studies have demonstrated the nonwetting ability of lotus leaf surfaces by heterogeneous wetting models by directly replicating or mimicking superhydrophobic surfaces commonly observed in nature, and were developed in 1944 by Cassie and Baxter.

Figure 4 (a) is a schematic diagram according to the proposed in the Cassie model of the presence of an air bag under the droplets. When the high contact angle and the low slip angle of the liquid drop placed on the surface due to the influence of the rough surface due to the presence of the microstructure are explained theoretically, the following equation is established.

COS qC-B = Fs COS qY (1-Fs)

 qc-b and qy are the c-b contact angle and the young contact angle of the uneven surface, respectively.

 fs is part of the project area of the solid surface in contact with the liquid.

 fs is always less than or equal to 1 and the contact angle of a bumpy surface is always greater than a flat surface.

On the other hand, Figure 4 (b) is a diagram illustrating the Wenzel model in the form that the liquid droplets placed on the rough surface is in complete contact with all surface areas including all microstructures. In this case, the contact angle between the solid surface and the liquid is formulated as follows.

COS qW = r COS qY

 qw and qy represent the contact angle and young contact angle of the wenzel model, respectively.

 r defines the roughness of the surface as a percentage of the project area of the solid surface, which is the actual area.

There can generally be between two states, the Wenzel state and the Cassie-Boxter (C-B) state. The specific roughness rc at this transition point is expressed as:

 rc = Fs (1- Fs) / COS qY

In general, when the surface roughness is smaller than the above specific roughness (rc), it belongs to the Wenzel state, whereas when r> rc, small droplets float on the mixed surface of gas and solid, which is in the C-B state. On the other hand, it is also possible to easily determine the rheological state of each surface from the slip angle. In other words, if the slip angle is small, the state is C-B. If the slip angle is large, the state is Wenzel. On the other hand, from the conditions of the superhydrophobic surface, the slip angle must be small in order for a surface to have the superhydrophobic property.

On the other hand, the PDMS substrate surface-modified directly with a femtosecond laser has a contact angle of about 165 ° and a slip angle of 3 ° or less, which means that it belongs to the C-B model shown in FIG. This condition is another result that is very similar to the surface state of lotus leaf observed in nature.

On the other hand, the contact angle of the negative replica substrate, which replicates the surface of PDMS surface modified directly, is 136.4˚, while the slip angle is very large. This is very unusual considering the fact that the roughness r of these two different PDMS substrates is not significantly different. This singularity can be understood to arise from the fact that the microstructures of the surfaces of the two different PDMS substrates are the same in shape but the degree of tilt they form with the substrate surface is completely opposite. The fs of the negative replicated substrate is much greater than that of the directly surface modified PDMS substrate. That is, the flat part of the cloned PDMS is on the surface in contact with the droplets on the substrate, whereas in the case of the direct surface-modified PDMS, the liquid is in contact with the upper part of the hemispherical microstructure. This phenomenon is consistent with the fact that the diameter of the microstructures is approximately 6 μm while the gaps between the protrusions are large enough between them, which is easily observed in the scanning electron microscope image shown in FIG. 2.

In summary, when comparing the surface roughness of the PDMS substrate and the negative replica substrate with respect to the specific roughness rc that forms the transition between the Wenzel state and the CB state, the rc and the negative surface of the negative replica were directly modified with the rc of the PDMS plate. It can be said that it is larger than, syn. In other words, it can be assumed that the surface of the negative replica is completely wet, which can be explained by the wenzel model. Figure 4 (c) is a picture of the droplet on the negative replica. This hypothesis is further supported by the fact that negative replica plates show relatively large contact angles but very large slip angles.

The surface-modified PDMS surface through the proposed process of the present invention shows high contact angle and very low slip angle, which are typical superhydrophobic characteristics, which clearly demonstrates the usefulness of the proposed technique. In particular, the microstructure of the surface of the PDMS substrate, which is directly surface-modified, is not only the size of the nanostructure on the microstructure, but also the distribution of the microstructure like the lotus leaf in nature. In addition, the positive duplicated substrate manufactured using the modified PDMS substrate as a master also shows a super water-repellent property with a significant meaning. This has shown empirically that the technique of the present invention can easily achieve high productivity. Another interesting result, on the other hand, is that the negative replication PDMS is in the Wenzel state and has a high contact angle while the slip angle is high.

As described above, the technique of the present invention can construct a polydiemthyl silane (PDMS) surface that mimics the ultrafine structure of a lotus leaf in a natural state, especially under ultrafast laser fluence of moderate strength. It was confirmed that the embodiment. In particular, the surface microstructure of the surface-treated PDMS is realized that a very rough surface state is realized by properly arranging the nano-sized microstructure on the micro-sized microstructure, which is the same as that of the superhydrophobic surface found in nature. Can be. The processed PDMS surface showed super water-repellent properties, and the contact angle was 165˚ and the sliding angle was found to be superhydrophobic. In addition, a negative replica obtained by replicating the surface of a processed PDMS as a master exhibits a large contact angle hysteresis with a relatively high contact angle of 90 ° while having a relatively large contact angle of 136 °. Found. In addition, it was confirmed that the negative replica (positive replica), which reproduced it again, maintains the superhydrophobic surface-treated with the first ultrafast laser. From the above results, the ultrafast laser surface treatment technology of the present invention proved to be a very useful technique that can be applied to the production of a large amount of superhydrophobic surface.

5 is a graph showing the change of the contact angle and the sliding angle by controlling the fluence of the ultrafast laser. The fluence of the ultrafast lasers having a contact angle of 90 ° to 170 ° is 2 to 8 J / cm ² , and the fluence of the ultrafast lasers having a sliding angle of 3 ° or less is 4 to 8 J / cm ² . have.

Figure 1 is a flow chart for the process of giving a super water-repellent property to the surface of the PDMS substrate through the ultrafast laser surface modification process and its replication process.

Figure 2 is a scanning electron microscope image of PDMS (a-b) and its negative (c-d) and positive (e-f) replication surface directly surface-modified using an ultrafast laser.

3 is an optical microscope image of water droplets dropped directly on the surface of the PDMS (a) and its negative (b) and positive (c) replica surface modified using an ultrafast laser.

4 (a) and (b) are schematic diagrams illustrating Cassie-Baxter and Wenzel models, which are two different models used to explain rheological properties depending on the presence of microstructures on the surface, respectively. Is a schematic diagram for explaining the state of the surface of the negative replication PDMS substrate.

5 is a graph showing the change of the contact angle and the sliding angle according to the fluence control of the ultrafast laser.

Claims (8)

a) Microsized microstructures of several hundreds of microns or less have nano-sized microstructures of several hundreds or hundreds of micrometers and have 90-170 degrees by irradiating beams of ultrafast lasers on the surface of polydimehylsiloxane (PDMS) substrates. Replicating in the same manner as the surface of the substrate by filling and curing the polymer mold on the surface of the surface-modified substrate with the superhydrophobic surface-modified substrate as a base material having a super-water-repellent surface having a contact angle of 3 ° and a sliding angle of 3 ° or less; b) separating the duplicated mold from the substrate; c) filling the polymer mold on the duplicated surface of the duplicated mold with the separated duplicated mold as a base material and curing the duplicated mold in the same manner as the face of the duplicated mold; d) repeating step c); Super water-repellent surface modification method using an ultra-fast laser, characterized in that comprises a. The method of claim 1, The ultrafast laser is a super-hydrophobic surface modification method using an ultrafast laser, characterized in that having a few ~ hundreds femtosecond pulse. The method of claim 2, The wavelength of the ultra-fast laser beam is 700 to 1100 nm, the pulse width is 100 to 700 fs, the substrate feeding speed is 3 to 5 mm / sec, the spacing between the laser beam spots is 3 to 20 μm, and femtosecond laser Chromatic aberration (NA) of the objective lens for adjusting the focus of the beam is 0.1 ~ 0.2, the size of the laser beam spot on the surface of the substrate is a super water-repellent surface modification method using an ultra-fast laser, characterized in that 6 ~ 20 ㎛. The method of claim 3, wherein Fluorescence of the ultra-fast laser having a contact angle of 90 ° to 170 ° is a super water-repellent surface modification method using an ultra high speed laser, characterized in that 2 to 8 J / cm ² . The method of claim 4, wherein The super water-repellent surface modification method using an ultra-high speed laser, characterized in that the average number of laser pulses irradiated to the substrate surface is 1.5 ~ 2.5. The method of claim 3, wherein The fluence of the ultra-fast laser having a sliding angle of 3 ° or less is 4 to 8 J / cm ² Super-water repellent surface modification method using an ultra-fast laser, characterized in that. The method of claim 4, wherein The super water-repellent surface modification method using an ultra-high speed laser, characterized in that the average number of laser pulses irradiated to the substrate surface is 1.5 ~ 2.5. delete

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