Method for controllably preparing micro-nano wrinkled structure based on three-axis loading and product thereof

Abstract

The present invention discloses a method for controllably preparing micro-nano wrinkled structures based on triaxial loading: First, a flexible organic polymer material is prepared and pre-loaded strain is applied to it on an equiangular triaxial mechanical device. Then, a metal thin film is deposited using a magnetron sputtering instrument, or the surface of the substrate is modified into a rigid silica-like thin film using ultraviolet-ozone (UVO) technology. At the same time, releasing the pre-loaded strain will generate different surface wrinkled structures and distributions compared to uniaxial and biaxial loading. The present invention realizes the controllable preparation of micro-nano wrinkled structures based on triaxial loading by driving material self-assembly with mechanical stress. This preparation method is simple, low-cost, short-cycle, and easy to control.

Description

Technical Field

[0001] The present invention relates to a method for controllably preparing micro-nano wrinkled structures based on triaxial loading and its products, belonging to the field of nanomanufacturing. Background Art

[0002] Surface self-assembled micro-nano wrinkled structures are ubiquitous in nature and daily life. For example, the large-scale wrinkles and micro-nano scale papilla structures on the lotus leaf surface, the sub-millimeter scale lamellar structures on the gecko's toes, and other structures such as the placoid scale grooves on the shark's body surface, the fine spiral nano-groove structures on the setae of the water strider's toes, etc. all exhibit the self-assembly characteristics of surface structures (W.G. Bae, H.N. Kim, D. Kim, et al. Scalable multiscale patterned structures inspired by nature: The role of hierarchy [J]. Adv. Mater., 2014, 26: 675–700.). Inspired by nature, people began to imitate and prepare various surface self-assembled structures in the laboratory. Due to the significant advantages of self-assembled structures such as rapidity, large area, and low cost, various technical solutions for controllably preparing surface self-assembled structures have been developed.

[0003] When external mechanical stress is applied for regulation, uniaxial stress usually results in stripe-shaped structures with consistent orientation, simultaneous release of biaxial stress leads to maze-shaped structures, and sequential release of biaxial stress leads to herringbone-shaped structures (J. Yin, J. L. Yagüe, D. Eggenspieler, et al. Deterministic order in surface micro-topologies through sequential wrinkling[J]. Adv. Mater., 2012, 24: 5441–5446.). However, the controllable preparation of surface self-assembled structures under multiaxial stress has not been reported yet, and the formation and evolution mechanisms of more complex surface self-assembled wrinkled structures remain to be explored in depth. In addition, some studies have pointed out that based on uniaxial stress, the controllable preparation of two-dimensional surface structures can be achieved by sequentially changing the stress direction. For example, based on uniaxial loading, Pellegrino et al. used a sequential treatment strategy of plasma to orthogonally superimpose two one-dimensional surface structures to regulate a symmetric checkerboard structure (L. Pellegrino, S. Khodaparast, J. T. Cabral. Orthogonal wave superposition of wrinkled, plasma-oxidised, polydimethylsiloxane surfaces[J]. Soft Matter, 2020, 16: 595–603.). Then, a unique ripple structure was regulated by superimposing one-dimensional surface structures in the range of 0-90° (L. Pellegrino, A. Tan, J. T. Cabral. Ripple patterns spontaneously emerge through sequential wrinkling interference in polymer bilayers[J]. Phys. Rev. Lett., 2022, 128: 058001.). This sequential treatment strategy is based on simple uniaxial stress regulation, proposing a new idea for the controllable preparation of surface self-assembled structures, improving the complexity and diversity of surface self-assembled structures. However, this usually requires multiple steps, increasing the complexity of the experimental process and the preparation cost, and the surface structure is single, and the diversity of self-assembled structures on a single surface remains to be explored. Summary of the Invention

[0004] Objective of the Invention: Based on uniaxial and biaxial loading, this method proposes a method for controllably preparing micro-nano wrinkled structures under triaxial loading, regulating surface micro-nano wrinkled structures different from those under uniaxial and biaxial loading, and having significant distribution characteristics on the surface of a single thin film, thereby resulting in anisotropy of the friction characteristics and light diffraction patterns of the entire thin film surface with the distribution characteristics. In view of the current insufficient research on the controllable preparation of surface self-assembled structures under multi-axial stress, the present invention provides a method for controllably preparing surface self-assembled micro-nano wrinkled structures using an equiangular triaxial mechanical loading device. This method uses a triaxial mechanical loading device to form wrinkled structures on the thin film surface through the loading and release of pre-strain. The wrinkled size on the thin film surface is regulated by changing the thickness of the thin film. This experimental method is simple, low-cost, short-cycle and easy to implement.

[0005] Technical Solution

[0006] The objective of the present invention is achieved through the following technical solution, a simple method for controllably preparing wrinkled structures, including the following steps:

[0007] Step (1): Prepare a liquid silicone polymer material, and form an elastic flexible substrate after curing;

[0008] Step (2): Load the flexible substrate onto an equiangular triaxial stretching device, where any two stretching directions of the triaxial stretching device form an angle of 60 degrees, and apply the same tensile force simultaneously in the three stretching directions of the triaxial stretching device to stretch the flexible substrate to generate pre-strain on the flexible substrate;

[0009] Step (3): Deposit a metal thin film on the surface of the flexible substrate by magnetron sputtering;

[0010] Step (4): Reduce the tensile forces in the three stretching directions of the triaxial stretching device to 0 at the same rate to obtain micro-nano wrinkled structures on the surface of the flexible substrate.

[0011] The present invention also provides a method for controllably preparing micro-nano wrinkled structures based on triaxial loading, including the following steps:

[0012] Step (1): Prepare a liquid silicone polymer material, and form an elastic flexible substrate after curing;

[0013] Step (2): Load the flexible substrate onto an equiangular triaxial stretching device, where any two stretching directions of the triaxial stretching device form an angle of 60 degrees, and apply the same tensile force simultaneously in the three stretching directions of the triaxial stretching device to stretch the flexible substrate to generate pre-strain on the flexible substrate;

[0014] Step (3): On the surface of the flexible substrate, generate a rigid silica-like thin film using ultraviolet-ozone (UVO) technology;

[0015] Step (4) reduces the pulling forces in the 3 stretching directions of the triaxial stretching device to 0 at the same rate, obtaining a micro-nano wrinkled structure on the surface of the flexible substrate.

[0016] Preferably, in the step (1), the liquid silicone polymer material is any one of polydimethylsiloxane (PDMS) and Ecoflex TM silicone rubber. The preparation process includes mixing the main agent and the curing agent, stirring evenly and then removing air bubbles; the mass ratio of the main agent to the curing agent is 10:1 to 1:1.

[0017] Preferably, in the step (3), the deposited metal is any one of Ag and Ta.

[0018] The present invention also provides a micro-nano wrinkled structure product. At the center of the micro-nano wrinkled structure, there are multi-directional wrinkles pointing in 3 directions. At the corners and edges of the micro-nano wrinkled structure, there are unidirectional wrinkles with the same orientation in a corrugated shape. There is also a region where the unidirectional wrinkles transition to multi-directional wrinkles in the micro-nano wrinkled structure. The friction characteristics and light diffraction patterns of the micro-nano wrinkled structure show anisotropy along with the nano-wrinkle distribution on the entire film surface.

[0019] The present invention has the following advantages and beneficial effects:

[0020] (1) The preparation method of the present invention is simple, low-cost, short in cycle and easy to control;

[0021] (2) The micro-nano structural features prepared by the present invention can be used to controllably prepare various sizes;

[0022] (3) The micro-nano wrinkled structure prepared by the present invention is different from the uniaxial and biaxial loading conditions, and has significant distribution characteristics on a single film surface. Multi-directional wrinkles are formed at the center, and straight stripe wrinkles or corrugated wrinkles with the same orientation are formed at the corners and edges, and there is a transitional form from unidirectional wrinkles to multi-directional wrinkles. Description of the Drawings

[0023] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Later, some specific embodiments of the present invention will be described in detail in an exemplary but non-limiting manner with reference to the drawings. The same reference numerals in the drawings denote the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0024] Figure 1 is the flexible substrate after cutting, and the research area is an equilateral triangle with a side length of 25 mm.

[0025] Figure 2 It is a schematic diagram of the process for controllably preparing micro-nano wrinkles based on three-axis loading. First, the substrate is pre-stretched, then a metal thin film is deposited using a magnetron sputtering instrument or an ultraviolet-ozone treatment is performed to form a rigid silica-like thin film, and finally the pre-strain is released.

[0026] Figure 3 It is the wrinkled structure observed under an optical microscope after depositing a tantalum metal film on the substrate for 30 s using a magnetron sputtering instrument.

[0027] Figure 4 It is the wrinkled structure observed under an optical microscope after depositing a tantalum metal film on the substrate for 45 s using a magnetron sputtering instrument.

[0028] Figure 5 It is the wrinkled structure observed under an optical microscope after depositing a silver metal film on the substrate for 30 s using a magnetron sputtering instrument.

[0029] Figure 6 It is the wrinkled structure observed under an optical microscope after subjecting the substrate to ultraviolet-ozone treatment for 30 min.

[0030] Figure 7 It is the wrinkled structure observed under an optical microscope after subjecting the substrate to ultraviolet-ozone treatment for 60 min.

[0031] Figure 3 and Figure 4 are the first implementation examples: Figure 3 It is to observe, using an optical microscope, the wrinkled structure on the surface of the thin film after depositing a 30-s Ta film using a magnetron sputtering instrument on a pre-stretched substrate and simultaneously releasing the pre-strain; Figure 4 It is to observe, using an optical microscope, the wrinkled structure on the surface of the thin film after depositing a 45-s Ta film using a magnetron sputtering instrument on a pre-stretched substrate and simultaneously releasing the pre-strain.

[0032] Figure 5 are the second implementation examples: Figure 5 It is to observe, using an optical microscope, the wrinkled structure on the surface of the thin film after depositing a 30-s Ag film using a magnetron sputtering instrument on a pre-stretched substrate and simultaneously releasing the pre-strain.

[0033] Figure 6 and Figure 7 are the third implementation examples: Figure 6 It is to observe, using an optical microscope, the wrinkled structure on the surface of the thin film after subjecting a pre-stretched substrate to ultraviolet-ozone treatment for 30 min and simultaneously releasing the pre-strain; Figure 7 It is to observe, using an optical microscope, the wrinkled structure on the surface of the thin film after subjecting a pre-stretched substrate to ultraviolet-ozone treatment for 60 min and simultaneously releasing the pre-strain.

[0034] Figure 8 It reflects the surface wrinkles and their distribution characteristics of the sample with a deposition time of 30 s, the topographic image (left column), the friction force image (middle column) obtained by atomic force microscope (AFM) scanning, and the light diffraction pattern (right column) obtained under laser irradiation. Specific implementation manners

[0035] In order to make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0036] Embodiment 1

[0037] Taking the deposition of the metal thin film Ta as an example, the specific implementation manners of this method will be described in detail.

[0038] 1. Fabrication of the flexible substrate: Sylgard 184 (polydimethylsiloxane, PDMS, components: base agent and curing agent, mixing ratio: adjustable) potting adhesive from Dow Corning, USA, was used. In the experiment, 10 g of the base agent and 1 g of the curing agent (mass ratio 10:1) were mixed, stirred evenly with a glass rod and then left standing horizontally. After the bubbles were completely eliminated, 8 g of the mixture was poured into a round petri dish (cover diameter × bottom height: 90 × 16 mm) and heated at 70 °C for 4 h until completely cured. At this time, the thickness of the flexible substrate PDMS was about 1.2 mm.

[0039] 2. Cutting the flexible substrate as Figure 1 shown, the research area is an equilateral triangle with a side length of 25 mm, which was loaded onto an equiangular triaxial mechanical device and stretched 1 mm along each axis, corresponding to a prestrain of 4.4%.

[0040] 3. Sputtering deposition of the metal thin film: The sputtering instrument used in the experiment was an ultra-high vacuum magnetron sputtering instrument. The sputtering target Ta target was a pure metal disk with a diameter of 60 mm and a thickness of 3 mm. The prepared sample was placed on the sample holder in the vacuum chamber of the sputtering instrument. The vacuum chamber was closed, the mechanical pump was turned on, and the low vacuum was pumped down to 10 Pa. Then the molecular pump was turned on, and the high vacuum was pumped down to less than 2 × 10 -5 Pa. The cooling water circulation device was turned on, the argon gas cylinder was opened, the gas flow rate was adjusted, the working pressure was set to 0.5 Pa, the sputtering power was set to 50 W (deposition voltage U = 250 V, deposition current I = 0.2 A), and the deposition time (t) could be adjusted according to the experimental requirements. In this experiment, the deposition times were set to 30 s and 45 s respectively. After the deposition was completed, the sputtering power was set to 0, the molecular pump was turned off, the mechanical pump was turned off, and the cooling water circulation device was turned off. After the sample was naturally cooled to room temperature, it was taken out of the vacuum chamber.

[0041] 4. Release the preloaded strains in three directions simultaneously, and observe the wrinkled structures formed on the film surface using an optical microscope (OM).

[0042] (1) As Figure 3 and Figure 4 shown: Multiple types of surface wrinkled structures are observed under the optical microscope. The wrinkled structures at the center have multiple directions, and straight stripe wrinkles or corrugated wrinkles with consistent orientations are formed at the corners and edges, and there are transitional morphologies from unidirectional wrinkles to multi-directional wrinkles.

[0043] (2) By comparing different film thicknesses, it can be seen that as the film thickness (deposition time) increases, the surface wrinkle scale also increases.

[0044] 5. Based on the surface wrinkles and their distribution characteristics of the sample with a deposition time of 30 s, the topographic images (left column), friction force images (middle column) obtained by atomic force microscope (AFM) scanning, and the light diffraction patterns (right column) obtained under laser irradiation are as Figure 8 shown. Compared with the isotropy under uniaxial and biaxial loading, the friction characteristics and light diffraction patterns show anisotropy with the distribution characteristics on the entire film surface.

[0045] Example 2

[0046] Taking the deposited metal film Ag as an example, the implementation method is the same as that in Example 1.

[0047] As Figure 5 shown: Similar to the surface wrinkled structures of the metal Ta film, multiple types of surface wrinkled structures are observed under the optical microscope. The wrinkled structures at the center have multiple directions, and straight stripe wrinkles or corrugated wrinkles with consistent orientations are formed at the corners and edges, and there are transitional morphologies from unidirectional wrinkles to multi-directional wrinkles.

[0048] Example 3

[0049] Use ultraviolet-ozone to treat the substrate surface, and the specific implementation method of this method will be described in detail.

[0050] 1. Fabrication of the flexible substrate: Use the Ecoflex TM (Composition: main agent and curing agent, mixing ratio: 1:1) silicone rubber of SMOOTH-ON Company in the United States. In the experiment, 10 g of the main agent and 10 g of the curing agent (mass ratio 1:1) are mixed, stirred evenly with a glass rod and then left standing horizontally. After all the bubbles are completely eliminated, 12 g of the mixture is poured into a round petri dish (cover diameter × bottom height: 90 × 16 mm) and cured at room temperature. At this time, the thickness of the flexible substrate silicone rubber is about 2 mm.

[0051] 2. Cut the flexible substrate as Figure 1As shown, the research area is an equilateral triangle with a side length of 25 mm. It is loaded onto an equiangular triaxial mechanical device, and each axis is stretched by 5 mm, corresponding to a prestrain of 22%.

[0052] 3. Ultraviolet-ozone (UVO) treatment: The UVO type basic cleaning machine of CIF company was used in the experiment. The prepared samples were placed on the tray of the cleaning machine, the treatment time was set, and the switch was turned on. After the treatment was completed, the ozone neutralizer was turned on for ozone neutralization treatment. The treatment times in this experiment were 30 min and 60 min.

[0053] 4. Release the preloaded strains in three directions simultaneously, and observe the wrinkled structures formed on the film surface using an optical microscope (OM).

[0054] (1) As shown in Figure 6 and Figure 7 : Similar to the wrinkled structures on the metal film surface, various types of surface wrinkled structures were observed on the silica-like film under the optical microscope. The wrinkled structures at the center have multiple directions, and straight stripe wrinkles or corrugated wrinkles with consistent orientations are formed at the corners and edges, and there is a transitional morphology from unidirectional wrinkles to multi-directional wrinkles.

[0055] (2) By comparing different film thicknesses, it can be seen that as the film thickness (UVO treatment time) increases, the surface wrinkle scale also increases.

[0056] As described above, only some specific embodiments of the present invention are given, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. Method for controllably preparing micro-nano wrinkled structure based on triaxial loading, Characterized in that, Comprising the following steps: Step (1): Prepare a liquid silicone polymer material, and form an elastic flexible substrate after curing; Step (2): Load the flexible substrate onto an equiangular triaxial stretching device, where any two stretching axes of the triaxial stretching device form an angle of 60 degrees, and apply the same tensile force simultaneously in the three stretching directions of the triaxial stretching device to stretch the flexible substrate, so that the flexible substrate generates pre-strain; Step (3): Deposit a metal thin film on the surface of the flexible substrate by magnetron sputtering; Step (4): Reduce the tensile forces in the three stretching directions of the triaxial stretching device to 0 at the same rate, and obtain a micro-nano wrinkled structure on the surface of the flexible substrate.

2. Method for controllably preparing micro-nano wrinkled structure based on triaxial loading, Characterized by: Comprising the following steps: Step (1): Prepare a liquid silicone polymer material, and form an elastic flexible substrate after curing; Step (2): Load the flexible substrate onto an equiangular triaxial stretching device, where any two stretching axes of the triaxial stretching device form an angle of 60 degrees, and apply the same tensile force simultaneously in the three stretching directions of the triaxial stretching device to stretch the flexible substrate, so that the flexible substrate generates pre-strain; Step (3): Generate a rigid silica-like thin film on the surface of the flexible substrate by using ultraviolet-ozone (UVO) technology; Step (4): Reduce the tensile forces in the three stretching directions of the triaxial stretching device to 0 at the same rate, and obtain a micro-nano wrinkled structure on the surface of the flexible substrate.

3. The method for controllably preparing micro-nano wrinkled structure based on triaxial loading according to claim 1 or 2, Characterized in that: In the step (1), the liquid silicone polymer material is any one of polydimethylsiloxane PDMS and Ecoflex TM or silicone rubber. The preparation process includes mixing the main agent and the curing agent, stirring evenly and then removing air bubbles; the mass ratio of the main agent to the curing agent is 10:1 to 1:

1.

4. The method for controllably preparing micro-nano wrinkled structure based on triaxial loading according to claim 1, Characterized in that: In step (3), the deposited metal is any one of Ag and Ta.

5. The micro-nano wrinkled structure product prepared by the method according to claim 1 or 2, Characterized in that: The center of the micro-nano wrinkled structure has multi-directional wrinkles pointing in three directions, the corners and edges of the micro-nano wrinkled structure have unidirectional wrinkles with consistent orientation, there is also a region where the unidirectional wrinkles transition to multi-directional wrinkles in the micro-nano wrinkled structure, and the friction characteristics and light diffraction patterns of the micro-nano wrinkled structure show anisotropy with the distribution of nano-wrinkles on the entire thin film surface.

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