PRODUCTION OF STRUCTURED SURFACES

Abstract

Three-dimensionally structured surfaces starting from an elastic material by stretching, selective treatment of different surface regions and relaxation.

Claims

1.-15. (canceled)

16. A method for producing three-dimensionally structured surfaces, wherein the method comprises or consists of: a) providing an elastic material, b) stretching the material by a predetermined value and maintaining a stretched state, c) transferring a two-dimensional pattern to the elastic material in the stretched state or introducing a two-dimensional pattern into a surface of the elastic material in the stretched state, d) cancelling the stretching, causing the material to fold itself corresponding to the transferred or introduced pattern, e) optionally, molding of the patterned surface produced in d).

17. The method of claim 16, wherein the introduction of the two-dimensional pattern into the surface in c) is carried out as follows: c1a) protecting specific surface areas of the elastic material by covering or applying a protective material, c1b) allowing oxygen plasma or reactive gas to act on uncovered or unprotected surface areas, c1c) removal of the covering or protective material, or c2a) placing an irradiation mask between a radiation source and the elastic material, c2b) irradiation of the material in the stretched state with electromagnetic radiation for a specific duration and with a predetermined radiation intensity, c2c) removal of the irradiation mask.

18. The method of claim 17, wherein the elastic material is an uppermost layer of a workpiece consisting of at least two different materials.

19. The method of claim 17, wherein the irradiation mask, a duration of irradiation, a radiation intensity and/or a degree of stretching are set depending on the elastic material used.

20. The method of claim 17, wherein the irradiation mask, a duration of irradiation, a radiation intensity and/or a degree of stretching are determined experimentally, experimentally iteratively and/or iteratively by machine learning and/or computer simulations.

21. The method of claim 20, wherein the experimentally iterative determination comprises or consists of: i) specification of a desired three-dimensional surface structure for the defined elastic material, iia) proposal of a two-dimensional surface pattern which, after irradiation through an irradiation mask, should fold into a structure as similar as possible to the specification, and iib) proposing parameters for the duration of irradiation, the radiation intensity and/or the degree of stretching, iii) carrying out a) to d) according to a method for producing three-dimensionally structured surfaces, which method comprises or consists of: a) providing an elastic material, b) stretching the material by a predetermined value and maintaining a stretched state, c) transferring a two-dimensional pattern to the elastic material in the stretched state or introducing a two-dimensional pattern into a surface of the elastic material in the stretched state, d) cancelling the stretching, causing the material to fold itself corresponding to the transferred or introduced pattern, e) optionally, molding of the patterned surface produced in d). iv) comparing the structure obtained in iii) with the specified structure, v1) in case of sufficient match between the three-dimensional surface structure obtained in iii) and the specified surface structure, outputting the obtained product, v1a) optionally storing the structure proposed in iia) and/or the parameters proposed in iib) and the corresponding obtained three-dimensional surface structure, v2) in case of insufficient match between the three-dimensional surface structure obtained in iii) and the specified surface structure, repetition of ii) to iv) while changing the structure proposed in iia) and/or changing parameters proposed in iib) by an algorithm, v2a) optionally storing the structure proposed in iia) and/or the parameters proposed in iib) and the corresponding obtained three-dimensional surface structure.

22. The method of claim 20, wherein the iterative determination is performed by means of machine learning and comprises or consists of: I) specification of a desired three-dimensional surface structure for the defined elastic material, IIa) proposal of a two-dimensional surface pattern, which after irradiation through an irradiation mask should fold into a structure as similar as possible to the specification, by an algorithm, and IIb) proposal of parameters for the duration of irradiation, a radiation intensity and/or a degree of stretching by an algorithm, IIa) calculating the folding of the surface pattern proposed in IIa) using the parameters proposed in IIb) by means of a simulation program, IIIb) transfer of a calculation result as a learning data set to a neural network, IV) comparing the structure calculated in III) with the specified structure, V1) in case of sufficient match between the three-dimensional surface structure calculated in III) and the specified surface structure, outputting the surface structure proposed in IIa) and parameters proposed in IIb), VIa) optionally storing the structure proposed in IIa) and/or the parameters proposed in IIb) and the corresponding obtained three-dimensional surface structure, V2) in case of insufficient match between the three-dimensional surface structure obtained in III) and the specified surface structure, repetition of II) to IV) while changing the structure proposed in IIa) and/or changing the parameters proposed in IIb) by an algorithm, V2a) optionally storing the structure proposed in IIa) and/or the parameters proposed in IIb) and the corresponding obtained three-dimensional surface structure.

23. The method of claim 17, wherein the desired surface structure, the irradiation mask, the duration of the irradiation, the radiation intensity and/or the degree of stretching are specified and, starting therefrom, it is determined a) which material parameters an elastic material to be used must have, and/or b) which elastic material can be used.

24. The method of claim 21, wherein the two-dimensional surface pattern proposed in iia) or IIa) corresponds to at least one defined exposure mask.

25. The method of claim 22, wherein the two-dimensional surface pattern proposed in iia) or IIa) corresponds to at least one defined exposure mask.

26. The method of claim 17, wherein a covering, a protective material, or a mask is used whose recesses have a width of less than 1 mm.

27. The method of claim 17, wherein a covering, a protective material, or a mask is used whose recesses have a width of from 1 μm to 0.5 mm.

28. The method of claim 17, wherein a covering, a protective material, or a mask is used whose recesses have a width of from 50 μm to 500 μm.

29. The method of claim 17, wherein a covering, a protective material, or a mask is used whose recesses have a width of from 300 μm to 500 μm.

30. The method of claim 16, wherein the resulting structured surface has hierarchical folds, overhangs, channels, microfluidic channels, dimples and/or combinations thereof.

31. A workpiece with a structured surface, produced with the method of claim 16.

32. The workpiece of claim 31, wherein the structured surface has hierarchical folds, overhangs and/or microfluidic channels with smooth, rounded cross-section.

33. The workpiece of claim 31, wherein the workpiece comprises at least two layers, the surface-structured surface being the uppermost layer.

34. A method for optimizing structured surfaces by means of machine learning, wherein the machine learning after specification of a desired three-dimensional surface structure comprises or consists of: I) specification of a desired three-dimensional surface structure for an elastic material, IIa) proposal by an algorithm of a two-dimensional surface pattern that should fold into a structure as similar as possible to the specification after irradiation through an irradiation mask, and IIb) proposal of parameters for a duration of irradiation, a radiation intensity and/or a degree of stretching by an algorithm, IIa) calculating a folding of the surface pattern proposed in IIa) using the parameters proposed in IIb) by means of a simulation program, IIb) transfer of the calculation result as a learning data set to a neural network, IV) comparing the structure calculated in III) with the specified structure, V1) in case of sufficient match between the three-dimensional surface structure calculated in III) and the specified surface structure, outputting the surface structure proposed in IIa) and parameters proposed in IIb), VIa) optionally storing the structure proposed in IIa) and/or the parameters proposed in IIb) and the corresponding obtained three-dimensional surface structure, V2) in case of insufficient match between the three-dimensional surface structure obtained in III) and the specified surface structure, repetition of II) to IV) while changing the structure proposed in IIa) and/or changing the parameters proposed in IIb) by an algorithm, V2a) optionally storing the structure proposed in IIa) and/or the parameters proposed in IIb) and the corresponding obtained three-dimensional surface structure.

Description

FIGURE DESCRIPTION

[0159] FIG. 1 illustrates the fabrication of a workpiece using the method according to the invention. The photo-crosslinking of polymers and/or crosslinking via (oxygen) plasma treatment allows a controlled and local change of the surface hardness. To this end, FIG. 1 shows how an initially stretched (not shown here) material 1a,1b, for example a vinyl group-terminated polydimethylsiloxane (Sylgard® 184 PDMS-Kit) is selectively exposed or cured, in particular crosslinked, in different areas with the aid of a mask 2. In FIG. 1, this is shown by means of lightning symbols 5, which are intended to illustrate the UV radiation (or oxygen plasma or similar) (in the case of oxygen plasma, the mask 2 must be placed directly on the surface of the material, because otherwise it is cured equally everywhere). In this FIG. 1, the uncured material is indicated as filled area 1a, and the cured area of the material is indicated as shaded zone 1b. FIG. 1 also illustrates the influence of the distance of the mask from the surface of the material; because directly under the parts of the mask 2, the material in the upper part of FIG. 1 is also shown as hardened, but not to the same depth as in the areas not shielded by mask parts. This is because at a greater distance, the mask cannot fully shield the areas below it from UV radiation. The closer the mask is to the material, the sharper the boundary becomes, up to completely non-hardened areas under the areas shielded by the mask, as illustrated in the lower half of FIG. 1, where the mask 2 rests directly on the material (it is known to the person skilled in the art that the sharpness of the boundary also depends on which chemical reactions the hardening reaction is based on).

[0160] By the structure of the mask 2, illustrated here by bars of different widths, the influence of the UV radiation (or oxygen plasma, etc.) on certain areas of the surface is reduced and consequently a curing pattern/crosslinking pattern is created in the material.

[0161] The degree of hardening/crosslinking can be controlled by the duration and intensity of the radiation. The fold formation begins when the material relaxes to the unstretched state (not shown here.)

[0162] FIG. 2 illustrates in section a) a stretched polymer substrate with an unhardened zone 1a and a hardened and newly crosslinked, thus also stiffer, surface layer 1b (shaded). In the image shown, the cured layer 1b is slightly thinner in the central region. When the substrate relaxes (i.e., the stretching is cancelled), the stiffer, because hardened, layer folds, shown in sections b) and c). In this way, complex structures, such as channels in this case, can be created. Section d) illustrates how the structure can be transferred to other materials and inverted (here into sharp points) by molding with another material 3 (shown in check).

[0163] If no knowledge of the particular structure or the folding is yet available, the resulting structures can be predicted with modern computer simulations.

[0164] FIG. 3 exemplary shows the structure of a channel cross, which results when a cross-shaped weak point, i.e. a cross-shaped non-exposed or weakly exposed region is obtained in the stretched state. This folds upon relaxation to a cruciform channel structure. FIG. 3a shows a top view of the resulting cruciform channel structure, wherein the different lines represent contour lines, starting from the lowest point in the center of the figure. FIG. 3b shows a lateral section through the resulting structure just below the top of the 3.3 μm contour line of FIG. 3a. Here it can be clearly seen that the surface forms a channel, with the walls descending toward the center. The thick areas illustrate the hardened area, i.e. no hardening of the material took place in the center. FIG. 3c shows a three-dimensional representation of the cross-shaped channel structure shown in FIG. 3a, in which the line grid illustrates the deformations during relaxation.

[0165] FIG. 4 shows an example structure with dimples. Localized weak spots result in a regular dimple pattern, with the protrusions resulting from the weak spots defined during irradiation (or plasma treatment). FIG. 4a shows a top view of the resulting dimple structure, wherein the various lines represent contour lines, starting from the lowest point in the center of the figure. FIG. 4b shows a lateral section through the resulting structure at the level of the center of FIG. 4a. Here it can be seen that there is an unhardened area in the center. Towards the edges of FIG. 4, two nubs are indicated (partially shown). The thick areas illustrate the hardened area, i.e. no hardening of the material took place in the center. FIG. 4c shows a three-dimensional representation of the dimple structure shown in FIG. 4a, in which the line grid illustrates the deformations during relaxation.

[0166] FIG. 5 illustrates, in the form of a flowchart, a sequence for a machine-learning design as applicable to the present invention. A desired 3D structure is specified by the application or the user. It is illustrated how here a neural network then proposes a surface pattern that should fold into as similar a structure as possible. A simulation is then used to calculate how the pattern should fold at a given exposure. The result is passed to the neural network as a learning data set, and, if necessary (if this result does not match the 3D specification sufficiently), a new proposal is generated. Thus, an in-silico cycle (ISC) is created, in which new learning data sets for the neural network are constantly generated. Thus, each time the learning dataset of the neural network is extended, and the evolution of 3D structures is improved. The result pattern can then be checked or verified in the laboratory. From deviations between experiment and simulation, the parameters of the simulation can be improved.

LIST OF REFERENCE SIGNS

[0167] In the figures, the same reference signs mean the same materials, substances, etc. [0168] 1a elastic material, unhardened [0169] 1b elastic material, hardened [0170] 2 exposure mask [0171] 3 material for molding/molded material [0172] 4 (micro)channel [0173] 5 UV radiation (or oxygen plasma, etc.)

[0174] The present invention will now be explained in more detail with reference to the following non-limiting examples. The following non-limiting examples serve to set forth the embodiments embodied therein. It is known to the person skilled in the art that variations of these examples are possible within the scope of the present invention.

EXAMPLES

Example 1—Fabrication of a Channel Structure

[0175] A PDMS (Sylgard® 184) substrate block with an edge length of 4×4 cm and 3 mm thickness was stretched to 4.92 cm×4.92 cm. An aperture mask was placed on top, with square holes of 0.4 mm×0.4 mm. The web width was 0.1 mm.

[0176] The surface was then exposed to an oxygen plasma (100 W; 0.2 bar) for a duration of 10 minutes.

[0177] A workpiece was thus obtained consisting of a substrate block with a partially hardened but still stretched layer placed on its uppermost surface.

[0178] Thereafter, the stretching was cancelled and, upon relaxation to the unstretched state, the PDMS layer folded with shrinkage to its original size of 4×4 cm in a regular cross-shaped channel structure.

[0179] The resulting workpiece could be glued to a glass block.

Example 2—Production of a Dimpled Pattern

[0180] Analogous to Example 1, a polydimethylsiloxane layer was stretched using an isotropic stretcher. Deviating from Example 1, however, it was stretched to 5.2 cm, and a round hole mask with hole diameter 1 mm and hole spacing 5 mm was used. Thus, the surface was hardened in the non-shaded area. The fold formation started when relaxing to the unstretched state and a regular dimple pattern was formed.

[0181] The dimple pattern thus obtained was transferred inversely by molding. For this purpose, the structure was filled with an epoxy resin and the epoxy resin was allowed to cure. Subsequently, the epoxy resin was lifted off the “dimple surface”.

[0182] Two complementary inverse textured surfaces were obtained.