Structured nanoporous materials, production of structured nanoporous materials and use of structured nanoporous materials
阅读说明：本技术 结构化纳米多孔材料、结构化纳米多孔材料的制造以及结构化纳米多孔材料的应用 (Structured nanoporous materials, production of structured nanoporous materials and use of structured nanoporous materials ) 是由 依尚·希瓦尼阿 伊藤真阳 山本大辅 于 2019-03-13 设计创作，主要内容包括：本发明公开了一种用于制造结构化聚合物材料的方法。在该方法中,提供了一种包含基本上均质的前体聚合物材料的主体。在该主体内设置电磁辐射的干涉图案以形成部分交联的聚合物材料,干涉图案包含电磁辐射强度的最大值和最小值,因此干涉图案导致前体聚合物材料的空间差异交联,以形成具有相对较高交联密度的交联区域和具有相对较低交联密度的非交联区域,交联区域和非交联区域分别对应于电磁辐射强度的最大值和最小值。然后,使部分交联的聚合物材料与溶剂接触,以促使至少一些非交联区域的膨胀和开裂,从而形成含有孔的结构化聚合物材料。(A method for making a structured polymeric material is disclosed. In the method, a body comprising a substantially homogeneous precursor polymeric material is provided. An interference pattern of electromagnetic radiation is disposed within the body to form a partially cross-linked polymeric material, the interference pattern comprising maxima and minima of electromagnetic radiation intensity, whereby the interference pattern causes spatially-differentiated cross-linking of the precursor polymeric material to form cross-linked regions having a relatively high cross-link density and non-cross-linked regions having a relatively low cross-link density, the cross-linked regions and non-cross-linked regions corresponding to the maxima and minima of electromagnetic radiation intensity, respectively. The partially crosslinked polymeric material is then contacted with a solvent to cause swelling and cracking of at least some of the non-crosslinked regions, thereby forming a structured polymeric material containing pores.)
1. A method for making a structured polymeric material, the method comprising:
providing a body comprising a precursor polymeric material;
providing an interference pattern of electromagnetic radiation within said body comprising a precursor polymeric material to form a partially cross-linked polymeric material, said interference pattern comprising maxima and minima of the intensity of said electromagnetic radiation, said interference pattern thereby causing spatially-differentiated cross-linking of said precursor polymeric material to form cross-linked regions of relatively higher cross-link density and non-cross-linked regions of relatively lower cross-link density, said cross-linked regions and said non-cross-linked regions corresponding respectively to maxima and minima of the intensity of said electromagnetic radiation,
contacting the partially crosslinked polymeric material with a solvent to cause swelling and cracking of at least some of the non-crosslinked regions to form a structured polymeric material containing pores,
wherein the precursor polymeric material is substantially homogeneous.
2. The method of claim 1, wherein the precursor polymeric material consists of a single phase when the interference pattern of electromagnetic radiation is disposed within the body of precursor polymeric material.
3. A method according to claim 1 or claim 2, wherein the precursor polymeric material comprises one or more homopolymers, one or more copolymers and/or one or more block copolymers when the interference pattern of electromagnetic radiation is provided within the body of precursor polymeric material.
4. The method of claim 1 or claim 2, wherein the precursor polymeric material comprises substantially no block copolymer.
5. The method of any one of claims 1 to 4, wherein the precursor polymeric material comprises a photoinitiator operable to cause crosslinking of the precursor polymeric material upon exposure to visible light.
6. The method of any one of claims 1 to 5, wherein the solvent used to promote swelling and cracking falls outside of, but sufficiently close to, the hansen solubility spheres of the precursor polymeric material when drawn in hansen space to plasticize and swell the precursor polymeric material.
7. The method of any one of claims 1 to 6, wherein the precursor polymeric material is formed as a layer on a substrate, a surface of the substrate providing a reflective interface for providing the interference pattern.
8. The method of any one of claims 1 to 7, wherein a first region of the precursor polymeric material is selectively exposed to the electromagnetic radiation and a second region of the precursor polymeric material is not exposed to the electromagnetic radiation such that expansion and cracking occur only in the first region in which the structured polymeric material containing pores is formed.
9. The method of claim 8, wherein the second region is shielded from the electromagnetic radiation by a mask.
10. The method of claim 8, wherein the first region is selectively exposed to the electromagnetic radiation by a laser.
11. The method of any one of claims 1 to 7, wherein a first region of the precursor polymeric material is selectively exposed to electromagnetic radiation to form a first interference pattern having a characteristic first periodicity to form a layered porous structure having a corresponding first periodicity, and a second region of the precursor polymeric material is selectively exposed to electromagnetic radiation to form a second interference pattern having a characteristic second periodicity different from the first periodicity to form a layered porous structure having a corresponding second periodicity.
12. A method for making a structured polymeric material, the method comprising:
providing a body comprising a precursor polymeric material;
selectively exposing a first region of the precursor polymeric material to electromagnetic radiation to form a first interference pattern having a characteristic first periodicity;
selectively exposing a second region of the precursor polymeric material to electromagnetic radiation to form a second interference pattern having a characteristic second periodicity different from the first periodicity,
wherein the first and second interference patterns interact with the precursor polymeric material to form a partially cross-linked polymeric material, each interference pattern comprising maxima and minima of the intensity of the electromagnetic radiation, the interference patterns thereby causing spatially-differentiated cross-linking of the precursor polymeric material to form cross-linked regions of relatively higher cross-link density and non-cross-linked regions of relatively lower cross-link density, the cross-linked regions and the non-cross-linked regions corresponding to maxima and minima, respectively, of the intensity of the electromagnetic radiation,
the method further comprises:
contacting the partially crosslinked polymeric material with a solvent to cause swelling and cleavage of at least some of the non-crosslinked regions to form a hierarchical porous structure having a corresponding first hierarchical porous structure periodicity in the first region and a hierarchical porous structure having a corresponding second hierarchical porous structure periodicity in the second region, the second hierarchical porous structure periodicity being different from the first hierarchical porous structure periodicity.
13. The method of claim 12, wherein the first interference pattern and the second interference pattern are formed by electromagnetic radiation of different incident angles, or different wavelengths, or both.
14. Use of a nanoporous material having a plurality of lamellae, adjacent lamellae being separated by an intermediate spacer layer, wherein the spacer layer comprises an array of spacer elements integrally formed with and extending between adjacent lamellae, the spacer layer having interconnected pores extending within the spacer layer, the lamellae and spacer layer being operable to reflect illumination light, for displaying an image.
15. The use of claim 14, wherein a first region of the nanoporous material has adjacent flakes separated by a first characteristic spacing and a second region of the nanoporous material has adjacent flakes separated by a second characteristic spacing different from the first characteristic spacing, such that the first and second regions exhibit different structural colors under white light illumination.
16. Use of a nanoporous material having a plurality of lamellae, adjacent lamellae being separated by an intermediate spacer layer, wherein the spacer layer comprises an array of spacer elements integrally formed with and extending between adjacent lamellae, the spacer layer having interconnected pores extending within the spacer layer, for conducting a fluid along the spacer layer.
17. Use of a nanoporous material having a plurality of lamellae, adjacent lamellae being separated by an intermediate spacer layer, wherein the spacer layer comprises an array of spacer elements integrally formed with and extending between adjacent lamellae, the spacer layer having interconnected pores extending within the spacer layer, wherein at least one spacer layer is exposed at the surface of the nanoporous material, the exposed spacer layer providing the hydrophobic surface.
18. A polymer structure having a plurality of lamellae, adjacent lamellae being separated by an intermediate spacer layer, wherein the spacer layer comprises an array of spacer elements integrally formed with and extending between adjacent lamellae, the spacer layer having interconnected pores extending within the spacer layer, wherein the lamellae are substantially non-porous.
19. A polymer structure having a first region and a second region adjacent to the first region, wherein the first region differs from the second region in that the first region is a nanoporous material having a plurality of lamellae, adjacent lamellae being separated by an intermediate spacer layer, wherein the spacer layer comprises an array of spacer elements integrally formed with and extending between adjacent lamellae, the spacer layer having interconnected pores extending within the spacer layer.
20. The polymer structure of claim 19, wherein the first region is formed as a track.
21. A polymer structure having a first region and a second region, each of the first and second regions having adjacent lamellae separated by an intervening spacer layer, wherein the spacer layer comprises an array of spacer elements integrally formed with and extending between adjacent lamellae, the spacer layer having interconnected apertures extending within the spacer layer, wherein in the first region adjacent lamellae are separated by a first characteristic spacing and in the second region adjacent lamellae are separated by a second characteristic spacing different from the first characteristic spacing, such that the first and second regions display different structural colors under white light illumination of the same angle of incidence.
22. The polymer structure according to any one of claims 18 to 21, wherein the first region and the second region have substantially the same composition.
23. The polymer structure according to any one of claims 18 to 22, wherein the polymer structure is in the form of a layer, the first region and the second region extending through the thickness of the layer.
24. The polymer structure according to any one of claims 18 to 23, wherein the spacing layer has a porosity greater than a porosity of the sheet.
25. The polymeric structure of any one of claims 18 to 24, wherein the nanoporous material is a cross-linked polymeric material.
26. The polymer structure according to any one of claims 18 to 25 wherein the average thickness of the lamellae in the structure is at least 20 nm.
27. The polymer structure according to any one of claims 18 to 26 wherein the average thickness of the lamellae in the structure is at most 200 nm.
28. The polymer structure according to any one of claims 18 to 27 wherein the lamellae in the nanoporous structure have a periodic spacing of at least 40 nm.
29. The polymer structure according to any one of claims 18 to 28 wherein the lamellae in the nanoporous structure have a periodic spacing of at most 1000 nm.
30. A polymer structure according to any one of claims 18 to 29, wherein the spacer elements are substantially solid cylindrical in structure.
31. A microfluidic device comprising the polymer structure of any one of claims 18 to 30.
32. A security document incorporating a polymeric structure according to any one of claims 18 to 30.
Technical Field
The present invention relates to structured nanoporous materials, methods of making structured nanoporous materials, and applications of structured nanoporous materials. Such materials have utility in various technical fields, in particular but not exclusively in optical technology, for example for anti-counterfeiting measures, and in microfluidic technology, for example for diagnostic applications.
Background
Disclosure of Invention
Technical problem
Drawings
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
fig. 1 shows a cross-sectional SEM image of a crack lithographic structure formed in a polystyrene film using Phenanthrenequinone (PQ) as a photocrosslinker, the film being exposed to different wavelengths of light (340, 385, 395, 405nm, from left to right in fig. 1) prior to immersion in glacial acetic acid.
Fig. 2 shows the corresponding structural colors of the film shown in fig. 1.
FIG. 3 is a graph of FIG. 3 depicting solvents that can be used for crack lithography on polystyrene films relative to Hansen solubility spheres.
FIG. 4 illustrates how the distance between layers of a crack lithographic structure decreases with increasing molecular weight.
FIG. 5 shows an image of ethanol percolation flow along a channel formed by crack lithography.
FIG. 6 an image of a mixed solution of rhodamine dye and 50nm polystyrene fluorescent gel flowing along a channel similar to that shown in FIG. 5 is shown in FIG. 6.
FIG. 7 shows cross-sectional SEM images of crack lithographic structures formed in various resists. (a) Polystyrene, (b) poly-4-chlorostyrene, (c) polyfluorostyrene, and (d) a styrene block copolymer, polystyrene-b-poly (acrylic acid). The scale of these images is the same and is shown in fig. 7(a) on a 500 μm scale.
FIG. 8 plots the reflected intensity versus wavelength of incident light for a crack lithographic structure formed using interference patterns generated using different wavelengths of incident light in the resist.
FIG. 9 is a graph showing the relationship between the Bragg peak wavelength and the light source wavelength for various resist compositions.
Fig. 10 shows a phase diagram of a crack lithographic structure (also referred to as COS structure) formed based on composition and molecular weight.
Fig. 11 shows a cross-sectional SEM image of a crack lithographic structure formed on an aluminum foil substrate.
FIG. 12 is a cross-sectional SEM image of a crack lithographic structure formed on a mirror glass substrate.
FIG. 13 left hand image (left hand image) of FIG. 13 shows an SEM cross-sectional view of a polystyrene-based crack lithographic structure prior to etching. The right hand image (right image) shows the corresponding structure after etching.
Fig. 14 left-hand image of fig. 14 shows a SEM cross-section of a poly (pentafluorostyrene) -based crack lithographic structure. The right hand image shows the corresponding structure after etching.
Fig. 15-17 fig. 15, 16 and 17 summarize three types of applications of the disclosed material proposed in this work.
Fig. 18 shows a cross-sectional SEM image of a crack lithographic structure produced using a laser microbeam.
Fig. 19-24 illustrate the proposed evolution mechanism of the crack lithographic structure.
FIG. 25 further illustrates the crack photolithography process.
Fig. 26 shows a modification of fig. 25 in which a mask or plate film is placed over a portion of the resist and the remainder of the resist is exposed to incident light.
FIG. 27 shows that the crack lithographic structure is not limited to being supported on a reflective surface.
Fig. 28 shows a schematic cross-sectional perspective view of the CL channel, while demonstrating structural color and microfluidic flow.
Fig. 29 shows an exemplary image of a CAD file from a microfluidic pattern to be written into a resist.
Fig. 30 shows a microfluidic pattern image corresponding to fig. 29, where resist has been written and developed by a CL process.
FIG. 31 shows a graph of Hansen parameters corresponding to the solvents listed in Table 4 for developing crack lithography in Polystyrene (PS). Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
FIG. 32 shows a graph of Hansen parameters corresponding to the solvents listed in Table 5 for developing crack lithography in Polycarbonate (PC). Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
FIG. 33 shows a graph of Hansen parameters corresponding to the solvents listed in Table 6 for developing crack lithography in PMMA. Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
FIG. 34 shows a graph of Hansen parameters corresponding to the solvents listed in Table 7 for developing crack lithography in Polysulfone (PSF). Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
Detailed Description
Detailed description of the preferred embodiments and other optional features of the invention
The present disclosure provides a description of the principle of forming new basic structures. This disclosure is provided to provide the inventor with the clearest thought of what is believed to be the underlying mechanism of the preferred embodiments of the invention at the time of writing this document, without being bound by theory. In the described embodiments, this mechanism is exploited to create regular heterostructures by controlled nanoscale explosive rupture.
Some preferred embodiments are described in the context of a lithographic process. The conventional concept of photolithography is to selectively expose a photosensitive film to light using a mask and then remove the exposed or unexposed areas. Herein, we report a new method, sometimes referred to herein as "crack lithography", in which exposed regions of a film are expanded by photo-induced stress to create a precise three-dimensional porous structure that exhibits structured color characteristics and the ability to act as a microfluidic channel. The development of optical elements and microfluidic chips has been initiated by simple techniques, which are the mainstay of inkless printing, counterfeiting techniques and medical diagnostics.
Photolithography is the main technique for fabricating ultra-fine patterns for semiconductor devices, microelectronics, and liquid crystal displays1. It is also from micro-electro-mechanical (MEMS) to micro-fluidic systemsOther new technological advances. In a typical photolithography process, a designed pattern is printed onto a photoresist and exposed to ultraviolet-visible light or an electron beam. After a chemical or physical development process, the resist is selectively removed and a topographical pattern is created on the substrate. Traditionally, resists are referred to as negative or positive resists2. For negative tone resists, the exposed resist may survive development, removing the unexposed resist. For positive resists, the unexposed resist may survive development, removing the exposed resist. As discussed in more detail below, the method of crack lithography is similarly to expose a portion of the polymer layer to electromagnetic radiation and develop the characteristic microstructure only in the exposed portion.
There has also been much research effort in creating three-dimensional structures with photonic crystal optical properties. However, for this purpose, classical lithographic techniques employing selective material removal in planar films are limited to layer-by-layer structure development3. A better approach involves applying a 3-D interference pattern in a thin film4-6So that all exposed resist material can be removed to develop the photonic structure. Although complex layered photonic structures can be developed in this way, the technique requires precision and in practice it is often difficult to efficiently replicate structures over large areas.
Here we present a broad technical platform by showing a novel lithography technique in the preferred embodiment. Crack lithography can create highly ordered layered porous structures in polymer films, creating printable areas of pigment-free, structural color. Crack photoresists have similar development steps as conventional photolithography, i.e. resist film formation, selective area exposure and subsequent solution development. This therefore makes it possible to easily employ crack lithography using existing technical infrastructure.
Crack lithography is based on the findings of some inventors and has been previously reported to produce a layered porous structure7,8. In the initial discovery, this layered structure was formed by a highly specific environment. Here, we report thatTo form such porous layered structures, and to a great extent to a wide range of materials and situations. This leads to a printing method of photonic crystal type structures that can be applied in microfluidic chips as well as thin transparent flexible films.
In this disclosure, some of the embodiments are demonstrated using Polystyrene (PS), other styrenic polymers, Polycarbonate (PC), poly (methyl methacrylate) (PMMA), and Polysulfone (PSF). The inventors have found that even this common polymer is able to form highly periodic porous photonic structures by a mechanical cleaving process. Cracking is a phenomenon observed during mechanical deformation of plastic materials9-11. In crack lithography, a polystyrene film (or a polymer blend containing styrene, or other suitable polymer) is deposited on a reactive surface, similar to classical lithography, and then patterned by exposure to light and solvent. However, during crack lithography, interference patterns of high and low light intensities are generated within the mold section of the exposed film due to interference between incident light and backreflected light from the substrate. When UV light is used as a light source and Polystyrene (PS) is used as a resist, the PS is crosslinked at high light intensity points.
Fig. 1 shows a cross-sectional SEM image of a crack-lithographically-structured formed in a polystyrene film using Phenanthrenequinone (PQ) as a photocrosslinker, the film being exposed to different wavelengths of light (340, 385, 395, 405nm, from left to right in fig. 1) prior to immersion in glacial acetic acid. Fig. 1 shows the growth period in a layer. SEM images of the films had the same magnification (
Another photocrosslinker used in this work is 4,4' -bis (diethylamino) benzophenone (BDABP). Although our studies were initiated with PQ, it was found that BDABP could be a more versatile photoinitiator in terms of miscibility with other polymers and more efficient absorption spectra at high wavelengths to shorten the crosslinking time.
Fig. 2 shows the corresponding structural color of the film shown in fig. 1. Viewing the film revealed a visible structural color difference due to the variation in the sheet period. The structural color and flake period exhibit bragg peaks in the specular reflectivity that increase with increasing wavelength of the original light.
An image may be created using structural color effects. The inventors used microbeams to write structural colors generated by crack lithography into a1 μm transparent PS film, which was then removed from its original reflective surface and placed on a glass slide for viewing, creating a 6mm square image. The image is clearly visible in high definition.
After exposure to a developing solvent (described later), the less crosslinked layer of the exposed film swells with the solvent, losing its glassy nature and becoming more flowable. The swelling-induced stress causes plastic deformation of the intermediate solvent-filled layer and manifests as crack-like fibrillation of the intermediate layer. If a photocrosslinking agent generating free radicals such as Phenanthrenequinone (PQ) is added to the polystyrene12,13Crosslinking may be caused to occur upon exposure to high wavelength visible light (as shown in fig. 2). Thus, by adding an appropriate wavelength sensitive photosensitizer, the pattern of high and low crosslink density regions applied can be tuned using the incident wavelength of light.
Environmental Stress Cracking (ESC) is a form of cracking that occurs when exposed to a weak solvent or when a weak solvent penetrates into a material, causing the material to deform and ultimately causing cracking. Generally, ESC occurs when a solvent does not dissolve but has a weak interaction with the material. This can be better characterized by the Relative Energy Difference (RED), which is the hansen solubility parameter and the relative index of the hansen solubility sphere14,15. According to the experiments of the inventors, it was found that a solvent capable of generating crack corrosion in a polystyrene film was drawn in a specific narrow region at a certain distance from hansen solubility spheres, which represent a solvent dissolving polystyrene in hansen solubility space. As shown in fig. 3.
Thus, the inventors' evaluation, for a particular polymer-solvent combination, can predict the formation of the morphology seen in crack lithography based on the tendency of the polymer to undergo environmental stress cracking upon exposure to the solvent under stress. Hansen considered this in reference 14, where hansen solubility parameters, Relative Energy Difference (RED) numbers and solvent molar volume (V) were used to assist in determining the region where ESC can be performed. We quote from the conclusion of this paper:
the plot of RED number versus molar volume V of the challenge chemical is taken as a method to correlate ESC in polymer. In these figures, there is a region of moderate absorption at the middle RED number, and ESC can occur. At higher RED numbers, the absorption is not large enough or at lower absorption the relaxation occurs preferentially. Lower RED numbers can severely attack or dissolve the polymer. The RED numbers result from HSP differences between challenge chemicals and polymers, with larger RED numbers indicating less equilibrium absorbance. V relatively reflects the transport (kinetic) phenomenon between the tested solvents. All other things being equal, smaller and more linear molecules will diffuse and absorb faster.
Further guidance regarding predicting ESCs in solvent-affected polymers is given in reference A1.
According to hansen solubility parameter theory, the solubility of a polymer depends on: energy (D) due to dispersion forces between molecules, energy (P) due to dipolar intermolecular forces between molecules, and energy (H) due to hydrogen bonds between molecules. These three parameters D, P and H form a three-dimensional Hansen solubility space. The solvent is represented as a point in hansen space and the polymer is described as a sphere of radius Ro.
The molar volume of the solvent is an important parameter for Environmental Stress Cracking (ESC). The higher molar volume of solvent has a lower ability to penetrate the polymer network and is difficult to initiate ESCs. The molar volume of the mixed solvent was calculated as the arithmetic mean of the component solvents based on the mixed volume ratio.
The Relative Energy Difference (RED) values listed above are calculated according to mathematical formula 1:
[ mathematical formula 1]
RED＝Ra/Ro
Thus, RED and V provide guidance for selecting suitable polymer and solvent combinations for generating ESCs. It can be appreciated that there is a complex relationship between RED and V and the occurrence of ESC. It can be said that a preferred embodiment of the present invention uses a polymer-solvent combination, wherein the solvent is located between the hansen solubility spheres of the polymer and the ESC + hansen solubility spheres of the polymer.
The areas of the film having a high crosslink density (corresponding to the high intensity areas of the interference pattern) induce pressure in the areas of the film having a low crosslink density (corresponding to the low intensity areas of the interference pattern). These low crosslink density regions remain glassy. Once sufficient mobility is obtained by the presence of the solvent, this is an additional driving force for the expansion of the low crosslink density regions and subsequent fibrillation. The same stress exists in the horizontal plane of the membrane, sometimes resulting in extensive cracking and buckling in the membrane. Notably, the same cracks as fibrillation were also observed in the voids of these large cracks.
When crack lithography was applied using polymers of different molecular weights, the interlayer distance was found to decrease with increasing molecular weight (fig. 4); it is common for stress induced cracking phenomena that longer cracks are observed in low molecular weight materials (especially below the polymer entanglement length).
Some of the most prominent features of crack lithographic structures are layered high refractive index layers separated by low refractive index regions. These bragg layers produce the phenomenon of structured color, where the color of the resonant reflection depends on the separation of the layers and is therefore directly related to the wavelength of the crosslinking radiation. However, polystyrene alone is not crosslinked in visible light, and thus it is not possible to obtain a visible structural color using polystyrene alone. However, many photosensitizers were tested, most notably Phenanthrenequinone (PQ), which is capable of absorbing under visible light conditions to generate cross-linking free radicals12,13. Using PQ as an additive and illuminating the film with light at higher wavelengths (up to 450nm) it is possible to create structured porous polymer films with large periodic intervals, resulting in a vivid photonic crystal structure color throughout the visible spectrum from UV to low IR (fig. 2). Since the wavelength of the light irradiated on the same polymer film can be simply changed, multicolor printing can be produced within the same film. This is in good agreement withThe situation where physical self-assembly of objects of excessively uniform size (e.g. colloidal crystals) produces structural colour16,17Different.
Using laser microbeams, crack lithography can prove powerful as a printing technology platform. A CAD-generated fine pattern (in this case, an image corresponding to Vermeer's picture of "pearl earring-worn maiden") was written directly onto the PQ-containing PS film using a 405nm wavelength laser. In one experiment, a single color demonstration was performed, using a single laser to write an image to the film. However, by using three wavelengths corresponding to RGB, full color can be printed on the same polymer film. The inventors have found that it is possible to produce a catalyst having a thickness of
Laser microbeam printing of crack lithographic structures is one way to create very small printed features with many applications, especially in the field of security printing. However, large area printing is also possible using masking techniques and broad monochromatic exposure. The inventors have found that structural colors can be printed on a 6 inch silicon wafer in tens of seconds. Thus, crack lithography offers another potential for convenient high-resolution printing.
The porosity within the layer creates a unique capability. The pores between the crosslinked multilayers are continuous in the horizontal plane of the membrane. Thus, by exposing the polymer film to the circuit-like pattern, a fluid channel may be formed. This property is very advantageous in the production of microfluidic channels. Microfluidic technology is rapidly expanding in the field of chemical and biological synthesis and analysis of low sample volumes, especially where only small amounts of sample are available. It is a rapidly developing field due to its economic advantages18,19. Nevertheless, perhaps the single greatest obstacle to microfluidic technology is that the development of microfluidic devices themselves is expensive. The most common method is to use classical lithography techniques, using conventional resists to transfer the fluid circuit pattern to a channel structure within a glass substrate. The PDMS layer was then bonded to the entire glass plate to create a closed channel circuit20,21. This entire multi-step process can be circumvented by printing porous channel circuits directly into the polymer film using crack lithography.
In one experiment, the inventors printed the microfluidic channels directly in a polymer film with a thickness of about 2 μm. In this method, no separate step is required to close the microfluidic channel. The channel height can be freely adjusted by changing the wavelength of the illuminating light, so that in principle the channel height can be varied in the flow.
Figure 5 shows an image of ethanol flow along the channel permeate (
Crack lithography is performed in resists that can produce photocrosslinking. We have demonstrated that this technique can be used with other members of the styrene family, including poly (pentafluorostyrene) and penta (chlorostyrene). An example is shown in fig. 7. This suggests that we can independently alter the mechanical and chemical properties of the porous channel, for example to make it more hydrophobic. Thus, the resist may contain additives as long as it does not interfere with the overall crosslinking ability by adverse phase separation (see FIG. 10 on PS-PMMA blend). It can also be generated in copolymeric materials where the phase separation can be more controlled. This crack was also demonstrated in polystyrene-b-polyacrylic acid (PS-b-PAA), resulting in a microfluidic channel with a more hydrophilic interior (fig. 7).
So far we have reported structures grown on silicon wafers, which are convenient reflective surfaces that can be handled. Any substrate can be used to develop crack lithography as long as it is reflective. We have demonstrated the printing process on metal, aluminum foil and glass (fig. 11 and 12, respectively).
The film can also be peeled off from the support layer in pure water without damaging the development structure. As long as the film is sufficiently thick, it can be considered self-standing.
Another feature of crack lithography is that the intermediate layer is bridged by nano-scale pillars. As shown in fig. 13 and 14, the columnar structure may be exposed by surface etching and lift-off. This structure can be used as a Cassie state, has air pockets on the surface to prevent wetting, and exhibits superior hydrophobicity. When crack lithography is applied using poly (2,3,4,5, 6-Pentafluorostyrene) (PFS) having hydrophobicity as a resist, a maximum contact angle of 160 degrees is achieved. The developing solvent is as above. Crack lithography combines the advantages of bottom-up self-organization and top-down lithography. Such a superhydrophobic structure also tends to increase the area if a large light source is used, and a high-order structural texture having superhydrophobicity can be printed on the same surface if the characteristics of photolithography are used.
The standing wave interference pattern phenomenon is well known in nature and has in fact been considered to have so far a great stimulating effect on the development of good microstructures using classical lithography. Which is known to cause waviness in the sidewalls of such microstructures22,23. Strategies in classical lithography to prevent this problem include the use of an anti-reflective film (bottom anti-reflective coating-BARC) under the resist24. However, in our studies, we actually utilized these interference patterns to create a layered porous structure with high periodicity.
At the end of this section, we present crack lithography as a broad platform printing technique. By combining the principle of environmental stress cracking with interference-based crosslinking in thin films, we can create masked or laser-patterned layered porous structures in simple homopolymers as well as more complex chemical compositions with additional functionality. The simplest applications are small-scale inkless printing, such as found in the vast anti-counterfeiting industry, or easy preparation of microfluidic devices. However, the unique structure developed in crack lithography means that there are applications that utilize their mechanical structure or their function to act as a microreactor, or even their ability to act as a channel for a gas, liquid or even optical path.
Fig. 15, 16 and 17 summarize three types of applications of the disclosure suggested in this work. They are structural color, superhydrophobic applications, and liquid flow applications, respectively.
Materials and methods and further discussion
Specialty grade polystyrenes (PS, 16, 28, and 160kDa) were obtained from Polymer Source Inc. Commercial grades of polystyrene (35 and 192kDa), bisphenol A polycarbonate (PC, 45kDa), poly (methyl methacrylate) (PMMA, 120kDa) and polysulfone (PSF, 35kDa) were obtained from Sigma-Aldrich (USA).
Commercial grades of PS, PC, PMMA and PSF were purified according to the following protocol: 3g of polymer was dissolved in 50ml of solution (toluene for PS, chloroform for PC, PMMA and PSF) and sonicated for 30 min at 50 ℃. The solution was filtered through a 0.2 μm PTFE Membrane syringe filter (mdi Membrane Technology inc., India) with alumina powder in the syringe. The filtrate was mixed with 200ml DI water in a flask and shaken vigorously for 1 minute. The mixture was left to separate for 20 minutes, after which the water was drained. The water mix-drain step was repeated 4 more times. 200m of methanol was added dropwise to the solution to reprecipitate the polymer. The precipitate was collected by filtration (Whatman filter paper, grade 41, USA). The purified polymer was dried in a vacuum oven at 50 ℃ for 2 days and then stored in a desiccator.
Table 1 shows some exemplary combinations of resists and solvents used to demonstrate crack lithography. Table 8 summarizes the solubility parameters of the mixed solvents indicated by asterisks.
[ Table 1]
TABLE 1
Resist and method for producing the same
Casting solvent
Developing solvent
PS
Toluene, chloroform
Acetic acid, mixed solvent
PS/PMMA blends
Toluene, chloroform
Acetic acid, mixed solvent
PS-b-PMMA
Toluene, chloroform
Acetic acid, mixed solvent
PFS
Butyl acetate or ethyl acetate
Ethyl acetate MeOH 2:8
Poly (4-chlorostyrene)
Toluene
Acetic acid
PS/PQ
Chloroform, dichloromethane
Acetic acid, mixed solvent
PS/TS
Chloroform
Acetic acid, mixed solvent
PS-b-PMMA/PQ
Chloroform
Acetic acid, mixed solvent
PS/PMMA/PQ
Chloroform
Acetic acid, mixed solvent
Table 2 shows some combinations of polymers, photoinitiators and solvents for spin coating and for micro LED printing.
[ Table 2]
TABLE 2
Table 3 shows hansen parameter calculation details for different polymers and different solvents.
[ Table 3]
TABLE 3
Table 4 shows the results of developing crack lithography in Polystyrene (PS) using different solvents. Fig. 31 shows the corresponding hansen parameter map, in which the numbers assigned to each solvent in table 4 are shown. Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
[ Table 4]
TABLE 4
Numbering
Solvent(s)
Numbering
Solvent(s)
1
Acetic acid (aa)
●
13
2-propanol
×
3
Acetonitrile
×
14
THF
×
4
Butanol
×
15
Toluene
×
6
1-chloropentane
×
19
EtOH/1-Chloropentane (9/1, w/w)
●
8
Ethanol (EtOH)
×
20
Acetonitrile/1-propanol (1/1, w/w)
×
9
Ethyl acetate
×
21
EtOH/THF(9/1，w/w)
●
12
1-propanol
×
22
Ethanol/toluene (9/1, w/w)
●
Table 5 shows the results of developing crack lithography in Polycarbonate (PC) using different solvents. Fig. 32 shows the corresponding hansen parameter map, in which the numbers assigned to each solvent in table 5 are shown. Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
[ Table 5]
TABLE 5
Table 6 shows the results of crack development lithography in PMMA using different solvents. Fig. 33 shows the corresponding hansen parameter map, in which the numbers assigned to each solvent in table 6 are shown. Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
[ Table 6]
TABLE 6
Numbering
Solvent(s)
Numbering
Solvent(s)
1
Acetic acid (aa)
×
11
Methanol
×
2
Acetone (II)
×
12
1-propanol
×
7
Methylene dichloride
×
18
aa/Water (6/6, 7/6, 5/3, v/v)
×
8
Ethanol
×
18
aa/Water (5/4, 4/3, 3/2, v/v)
●
9
Ethyl acetate
×
Table 7 shows the results of developing crack lithography in Polysulfone (PSF) using different solvents. The corresponding hansen parameter plot is shown in fig. 34, which shows the numbers assigned to each solvent in table 7. Dots indicate successfully developed crack lithography, and crosses indicate unsuccessfully developed crack lithography.
[ Table 7]
TABLE 7
Numbering
Solvent(s)
Numbering
Solvent(s)
1
Acetic acid (aa)
×
15
Toluene
×
2
Acetone (II)
×
16
Acetone/aa (8/5, 13/5, 20/5, v/v)
●
7
Methylene dichloride
×
17
Acetone/methanol (3/2, 15/2, v/v)
×
9
Ethyl acetate
×
17
Acetone/methanol (15/9, 15/7, v/v)
●
12
1-propanol
×
1 crack corrosion process
The resists and developing solvents are listed in tables 1-8.
1-1 preparation of films
1-1-1PS
PS (20-35kDa, Sigma Aldrich) was dissolved in toluene (Aldrich) solution to form a 5-10 wt% PS solution. The PS chloroform or dichloromethane solution was then mixed with the photoinitiator 7.2
1-1-2 Polymer blends
Polymer blends of Polystyrene (PS) and poly (methyl methacrylate) (PMMA) consist of PS (35kDa or 20kDa, Sigma Aldrich) and PMMA (4kDa,8.6k or 15kDa, HORIBA STEC) in various mixing ratios. To crosslink PS and degrade PMMA under visible light, 0.8
1-1-3 other homopolymers
Butyl acetate or ethyl acetate was used for spin-coating solvent of poly (2,3,4,5, 6-Pentafluorostyrene) (PFS) and toluene (Aldrich) was used for solvent of poly (4-chlorostyrene).
1-2 spin coating
The solution was spin cast on a substrate with a mirror surface, such as a polished silicon wafer, metal, and glass, by a spin coater (MS-a100, Mikasa). Spin casting is known to leave residual stresses in the film; for clarity, the film is unstressed by high temperature annealing (e.g., 190 ℃ for polystyrene) prior to exposure to electromagnetic radiation for crosslinking.
1-3 crosslinking
The polymer film without added photoinitiator was exposed to UV light (wavelength 254 nm; CL-1000, UVP) to effect crosslinking. The polymer film containing the photoinitiator was exposed to visible light generated by an LED lamp (Thorlabs). The wavelengths of the LED lamps are 285, 300, 340, 375, 385, 395, 405, 420, 455 or 490nm, respectively. Alternatively, the polymeric film containing the photoinitiator is exposed to visible light generated by a laser. The beam size of the laser is varied by a plano-convex lens and/or a polymer film (such as PS-b-PMMA) is placed out of focus so that the beam is maximally expanded to a 7mm x 7mm square.
For micro-pattern printing, the film was exposed by an LED light source using a digital mask (maskless lithography tool D-light DL-1000GS/KCH, NanoSystemsolutions) or a laser lithography system (DWL 4000, Heidelberg Instruments Mikrotechnik).
1-4 development
After crosslinking the PS by UV or visible light, the film is developed by immersion in glacial acetic acid or other suitable solvent as shown in tables 1-8 for 10-180 seconds at room temperature.
2 analysis of
2-1 structural analysis
The structure of the resulting crack photolithography film was studied by scanning electron microscopy (FE-SEM; JSM-7500F, JEOL or SU8000, Hitachi, using an accelerating voltage of 15.0 kV) and using an ultraviolet visible spectrometer (MCPD-3700, Otsuka Electronics; using a 210-.
2-2 contact Angle
The surface energy was measured by contact angle gauge (DSA25S, KRUSS). CF at 89sccm by Scotch tape or by a reactive ion etcher (RIE-10NR-KF, SAMCO)4Flow rate, pressure of 10Pa and 50W/cm2The power of (2) is subjected to the peeling treatment.
2-3 flow assay
For flow channel studies, the flow of the solution was observed by optical microscopy (Axioscope a1 MAT, Carl Zeiss) or confocal microscopy (Nikon). The solution was injected from the scratch of the film.
3 further discussion of
Hansen solubility parameter analysis for crack lithography solvents.
Fig. 3 shows hansen solubility parameter analysis of crack lithography solvents. Toluene, which is a good solvent in hansen space, and a mixed solvent for successful development are plotted. The large spheres show the interaction radius of polystyrene. The shaded dots indicate acetic acid, and the black dots indicate the mixed solvent.
If crack lithography is to be induced in polystyrene, as shown in fig. 3, it is necessary to perform development using solvents having different solubilities compared to the solvents dissolving PS (those contained within the large spheres in fig. 3). That is, although it should not dissolve the film, it is necessary to select a solvent that will plasticize and swell the film. Table 8 summarizes some of the mixed solvents used in this work. Solvents that can be used for crack development are present in a relatively narrow range.
[ Table 8]
TABLE 8 Mixed solvent combinations that yield solvents with altered Hansen solubility parameters
Effect of molecular weight on crack lithography
Figure 4 shows the variation in the periodic spacing seen in the porous structure when other identical crack photolithography processes were carried out using different molecular weight styrenes.
The upper graph of fig. 4 shows electron microscope cross sections of polystyrene and polyfluorostyrene of different molecular weights that have undergone the same crack lithography process and have been irradiated using the same preliminary wavelength (254 nm). The greatest degree of cracking was observed in the low molecular weight samples, since the higher molecular weight polymers were more entangled and mechanically elastic to swelling. This observation is reflected in the spectral reflectance curves of these samples (as shown in the lower part of fig. 4), where bragg diffraction peaks are observed for low molecular weight samples at higher wavelengths.
Effect of Polymer composition on crack lithography
FIG. 7 shows a cross-sectional SEM image of crack lithographic structures observed in styrene homopolymer (polyfluorostyrene, poly 4-chlorostyrene) and styrene block copolymer polystyrene-b-poly (acrylic acid).
Figures 8-10 illustrate the use of polymer blends to form crack lithographic structures with polymer blends.
For the sample reported in fig. 8, a microscope image of the reflected color from a1 micron thick polymer blend film containing 82% or 89% polystyrene (Mw 35k) and 4% or 5% PMMA, respectively, in addition to 14% or 6% PQ or TX, was observed. These approximate ratios of PQ or TX can be used as photosensitizers to achieve the above results. The cast films were irradiated with light of different wavelengths from 254nm to 532nm before development with acetic acid. A change in structure color was observed indicating a different expansion of the layers within the crack lithographic structure. This fact is reflected in the plot shown in fig. 8, where the spectral reflectance data of the sample shows Bragg diffraction peaks (Bragg diffraction peaks) moving from UV through visible light and towards the IR range of the electromagnetic spectrum. In fig. 9, the spectral peaks of a PS/PMMA blend with the addition of sensitizers PQ and TX to shift the structural size of the crack lithographic structure from UV to visible light are plotted. FIG. 10 shows a phase diagram of crack lithographic structures formed from PS/PMMA blends. Squares and triangles indicate the locations where COS structures were observed (squares) and not observed (triangles), respectively. As above, different mixtures of PS and PMMA of different molecular weights are mixed in solutions and films of these solutions are subjected to a crack lithography process. In fig. 10, the x-axis corresponds to the ratio of PMMA in the blend. The total molecular weight (Mw) is shown on the y-axis and is the sum of the PS and PMMA molecular weights. The solid line is the estimated boundary line guiding the eyes. Insets (a) and (b) in fig. 10 show SEM cross-sectional views of successful crack lithography structures and failed films, respectively, of the PS/PMMA blend. Scale bar represents 500 nm. FIG. 10 shows that crack lithographic structures can be created in polymer mixtures depending on the molecular weight and mixing ratio of the components. In fact, the ability to observe crack lithographic structures may be related to the molecular mixing mechanism of the two polymers, as the boundary between a crack lithographic structure and a non-CL structure is similar in form to the cloud point boundary between miscible and immiscible phases of a two-component phase diagram.
Function of the substrate
Crack lithography has also been demonstrated on reactive substrates other than silicon. Fig. 11 shows a cross-sectional SEM image of a crack lithographic structure formed on an aluminum foil substrate. Fig. 12 shows a cross-sectional SEM image of a crack lithographic structure formed on a specular glass substrate. In each of fig. 11 and 12, a polymer film was used using a PS-b-PMMA resist, and the scale bar in each image represents 500 nm.
Super hydrophobic surface
Fig. 13 and 14 illustrate the use of this material to form a highly hydrophobic surface. FIG. 13 left hand image shows an SEM cross-sectional view of a polystyrene based crack lithographic structure prior to etching. The right hand image shows the corresponding structure after etching. The inset in each image shows the measurement of the contact angle between the surface and the water droplet. Before etching, the surface contact angle was 95 °. After etching, the contact angle was 140 °.
Fig. 14 left hand image shows SEM cross-sectional view of a poly (pentafluorostyrene) -based crack lithographic structure prior to etching. The right hand image shows the corresponding structure after etching. The inset in each image shows the measurement of the contact angle between the surface and the water droplet. Before etching, the surface contact angle was 105 °. After etching, the contact angle was 160 °.
Printing resolution
Fig. 18 shows a cross-sectional SEM image of a crack lithographic structure generated using a laser microbeam. The width of the laser microbeam is shown on the image. Fig. 18 shows that the development of the crack lithographic structure is sharply aligned with the laser microbeam.
Evolution of crack lithographic structures
Fig. 19-24 show the proposed mechanism of crack lithographic structure evolution.
It has been noted that crack lithography results from back reflection and interference of incident light, which results in standing wave phenomena inside the polymer film. The spacing of the equal intensity planes is given by λ/2n, where λ is the normal incident wavelength in the medium above the thin film. Fig. 20 shows a general case where θ is an incident angle with respect to a heavy line perpendicular to the substrate plane. n (or n (λ)) is the wavelength dependent refractive index of the material. Fig. 19 shows a case where light is incident at an angle perpendicular to the substrate.
The spacing of the planes can be varied by varying the wavelength of incidence, the angle of incidence, or the polymer material itself. Typically, the medium above the layer is air, but may also be other media, such as water or oil.
Fig. 20 shows a case where light is incident at an angle oblique to the substrate. The effect of this is to create a greater degree of separation between the planes.
As shown in fig. 21, in the plane of high
As shown in fig. 22, it is shown that the formation of the high
As shown in fig. 23, upon exposure to a solvent having a weak interaction with the uncrosslinked polymer to the extent of swelling or plasticization, the solvent penetrates into the low-density crosslinked
Environmental Stress Cracking (ESC) is the most common feature in plastics, but can also affect materials such as metals (e.g., hydrogen embrittlement). When a plastic under stress is exposed to a weak solvent that can penetrate into the polymer, the solvent can plasticize the weakest point of the material where the stress density is highest, allowing cracks to nucleate and grow. The way in which cracks develop is by the formation of voids and fibrils before the crack itself. The development of partial cracks can lead to an extended series of fibrils. This is schematically illustrated in reference S1 and experimental observations were made in polyethylene (reference S2) and polystyrene (reference S3). Although cracking and crack formation are generally undesirable in plastics, this is a very common feature of plastics under extended service. However, in some cases, ESC may be aggressively promoted to create new materials. The best known example is stretching a polymer film to produce well-defined fibrils and voids that can be used in film technology. Thus, the most common membrane separator in lithium ion batteries is actually a cracked polyethylene sheet.
During standard photolithography, the photoresist is exposed to light. The light is transmitted through the resist and reflected from the back of the substrate. Interference between the back-reflected light and the incident light creates standing waves of high and low light intensity within the film. The periodic difference in crosslink density results in uneven development of the photoresist walls during chemical development. There are many examples where such a wavy sidewall development is found without a backside anti-reflective coating (BARC). To avoid this effect, BARC coatings have been developed, which are essentially another layer of polymer between the resist and the support. By properly tailoring the properties of the BARC layer, light reflected from the support will interfere destructively with light reflected from the BARC layer, so that there is no back-reflected light. See, e.g., references S4 and S5.
Development of structural color for crack lithography
FIG. 25 further illustrates the crack lithography process. A crack lithographic resist 32, such as polystyrene, is deposited on the
The right hand portion of fig. 25 shows the final structure of the crack-photodefinable film after exposure to light and a developing solution (such as acetic acid). If light is incident on the
Fig. 1 shows the structure observed by cross-sectional electron microscope experiments when a polystyrene film with Phenanthrenequinone (PQ) as a photocrosslinker was exposed to different wavelengths of light (340, 385, 395, 405nm) before being immersed in glacial acetic acid. Fig. 1 shows the increased period of the layers (scale bar 500nm) by a cross-sectional SEM image of the film with common magnification. The unique structure color of each peak is represented in fig. 2 by the bragg diffraction peak associated with the structure. This phenomenon is not limited to polystyrene samples. This was also observed in polymer blends containing 80% polystyrene and 20% polymethylmethacrylate, as shown in figure 8. This was also observed in other blends of polystyrene and indeed in other polymers capable of crack lithography.
Fig. 26 illustrates a modification of fig. 25 in which a mask or stencil (tencel) 33 is placed over a portion of the resist and the remainder of the resist is exposed to incident light. After development in acetic acid, the crack
An alternative printing approach is to use focused light or laser light of a particular wavelength, power and angle incident on the resist for a programmable period of time and written in a particular pattern. This avoids the use of masks or templates. The inventors have simply demonstrated this by drawing lines in the resist (polystyrene). The sample was then exposed to acetic acid, revealing the drawn structure. More complex structures can be drawn, which can be pre-compiled by CAD or other graphic filesThe process. These documents were found to be faithfully written into the polymer film as a structural color. The intensity of the color that can be produced depends on the amount of energy deposited by the laser, which depends on the laser power flux (W/m)2) And duration of exposure to laser light (a) over a given area. The complexity of the CAD pattern is the subject of the author, and the pattern is faithfully reproduced into the resist pattern. The structured color pattern can be written simultaneously by using multiple laser sources of different wavelengths (using multiple angles of incidence if necessary).
FIG. 27 shows that the crack lithographic structure is not limited to being supported on a reflective surface. As long as the original resist film has mechanical elasticity, it can be taken out of the original process by further steps. This step may be performed by mechanically peeling off the substrate, or by a water displacement method or by another method that causes the resist film to be separated from the support. As an illustration of this, a complex monochromatic image was written by a crack lithography process onto a thick (2 micron) block copolymer film of thick polystyrene-b-polymethylmethacrylate, where the film was initially spin-coated on a glass support. After image development, the sample was immersed in water, whereby the water invaded into the space between the polymer and the support, leaving the polymer film on the water surface. Thereafter, the film was subsequently mechanically picked up on a transparent slide for analysis, showing that the image had been faithfully reproduced.
The structural color features of the Crack Lithography (CL) printing process are described in detail above. However, it is important to note that the areas where crack lithography exists contain a continuous pore path (in the plane of the film) that can be controlled by the crack lithography conditions. Within the porous path, an external material may be incorporated and/or flow may be facilitated. Thus, a CL process can be used to create a flow path such as that used in a microfluidic device. To demonstrate this, a suitable pattern was prepared from a CAD file and faithfully reproduced in the resist, and as shown in fig. 5 and 6, the flow of liquid through the channels can be demonstrated. These liquids may be aqueous or organic, and may even be of other types, as long as the material constituting the CL matrix is elastic to them. Also, gas can be flowed through the material and/or light can be flowed through the material (using the structure as a fiber channel). The main advantage of such a channel is that by the CL process the channel can be formed to be self-closing, which is a clear difference from using classical lithographic techniques, which require the connection of an upper sealing surface after the creation of the channel.
Fig. 28 shows a schematic cross-sectional perspective view of a CL channel formed by a
Fig. 29 schematically shows an example image of a microfluidic pattern CAD file to be written into resist. Fig. 30 schematically shows the corresponding image of the microfluidic pattern that has been written with resist and developed by the CL process, showing that the CAD file image is faithfully reproduced.
As already discussed and as shown in fig. 13 and 14, the surface energy of the CL surface can be changed by removing the upper layer of the CL structure. This may be done by mechanical stripping or using the surface of the tape, or may be done more systematically by using a vapor etching process. The structure directly below the CL surface consists of a plurality of pillars that create surface roughness, thereby increasing the hydrophobicity of the surface. Thus, using a patterned CL process, a mask (such as the circular mask in figure (d)) is used, followed by etching of the entire film by reactive ion etching, resulting in a surface with a water contact angle much higher than that of a non-CL surface. This results in a method of producing a superhydrophobic pattern on a film that exhibits differences in ice-forming or water repellency properties.
As shown in fig. 15-17, there are a number of possible advantages of CL structures that combine inherent CL structures with the ability to be printed using photolithographic techniques and that take advantage of the resulting structural properties, such as superhydrophobicity or structural color, as well as other properties of the structured material. For example, the structural color itself will change as the internal voids are filled with new materials of different refractive index. Thus, based on this filling of the inner hole, the structure can be used as a sensor.
Furthermore, the structure may be filled with reactive substances which may be converted to be more stable in the printed structure itselfThe chemical form of the compound. For example, if the printed wire is filled with a metal precursor (e.g., silver perchlorate (AgClO)4) It can be subsequently reduced to metallic silver by UV light (365nm), whereby a conductive circuit can be created without using a metal vapor deposition process. Thus, such a functionalized pattern can be used as a sensor. Such channels can be used to create porous gas channels, or as conduits for light channels, so the fiber lines can be printed using a CL printing process. It should also be noted that the mechanical properties of the CL structure will be different from the non-CL regions adjacent to the printed area. This makes it possible to create a pattern for directional cracking of the material or preferential absorption of stress in the printed area. It should also be noted that once the printed CL lines are prepared, another resist can be covered and a second layer of porous lines created. These two layers can then be joined together at strategic points so that a 3-dimensional route can be created.
The embodiments of the invention described primarily are presented in polystyrene-based polymer systems and additional disclosure is provided regarding PC, PMMA and PSF polymers. However, it is to be understood that the present invention has applicability in a wider compositional space. For example, any commercially available negative resist polymer (e.g., a resist polymer that crosslinks upon exposure to certain light with the aid of a photoinitiator present) is susceptible to crack lithography when used with a suitable solvent. Examples of such suitable materials include, but are not limited to: -
(1) Polyisoprene rubber crosslinked by photoreactive azide.
(https://en.wikipedia.org/wiki/Photoresist#Negative_photoresist)。
(2) SU-8 (epoxy polymer)
(3) Polyimide, polyimide resin composition and polyimide resin composition
(https://www.jstage.jst.go.jp/article/photopolymer/27/2/27_207/_pdf)
While the invention has been described in conjunction with the exemplary embodiments outlined above, many equivalent modifications and variations will be apparent to those skilled in the art given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the invention.
All references mentioned above and/or identified below are incorporated herein by reference.
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