Laser processing of switchable chiral microstructures and method of chiral switching

Abstract

The present application relates to the technical field of micro-nano machining, and more particularly to a laser processing method and a chiral switching method of a switchable chiral microstructure. The present application obtains a stimulus-responsive polymer as a processing material, then places the stimulus-responsive polymer on a processing substrate to form a processing surface, and processes the microstructure on the processing surface by using a femtosecond laser; then performs developing treatment on the processing surface to obtain a developed microstructure; and then places the developed microstructure in two different stimulus-responsive environments in sequence to perform self-assembly and chiral switching of the microstructure. The present application processes the stimulus-responsive polymer by using a femtosecond laser processing technology, so that the posts processed have different crosslinking densities in the two lateral regions, thereby realizing self-assembly and reversible chiral switching of the microstructure in different stimulus-responsive environments. The present application solves the problem that the existing microstructure is difficult to realize chiral switching.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-nano processing, and more particularly to a laser processing method of a switchable chiral microstructure and a chiral switching method. BACKGROUND

[0002] Chirality refers to the phenomenon that an object cannot coincide with its mirror image. In the field of molecular medicine, even if the same molecular structure, different chirality will lead to different physical properties and chemical properties, that is, enantiomers of chiral drug molecules have different pharmacological effects - effective or toxic. For example, R configuration (right-handed) thalidomide has a calming effect and can reduce nausea, but S configuration (left-handed) thalidomide not only has no calming effect, but also causes fetal malformation. For another example, chiral pesticides usually only have one effective type, and other types are ineffective or pollute the environment. The detection of chiral substances has great value, and the detection of chiral substances can be realized based on chiral structure, so it is very important to study the method of switching the structure chirality.

[0003] Among the current microstructure processing methods, focused ion beam (FIB) technology, electron beam lithography (EBL) technology, and traditional femtosecond laser processing technology are several commonly used ways. Among them, the first two ways have the disadvantages of high cost and expensive equipment, and the microstructures processed by the two ways have randomness when self-assembled, which is difficult to tune; the microstructure processed by the last way has a single rotation direction and does not have tunable performance.

[0004] Therefore, how to realize the chiral switching of the microstructure is the focus of the present application. SUMMARY

[0005] Therefore, it is necessary to provide a laser processing method of a switchable chiral microstructure and a chiral switching method in view of the problem that the existing microstructure is difficult to realize chiral switching.

[0006] The present application adopts the following technical solutions:

[0007] The present application discloses a laser processing method of a switchable chiral microstructure and a chiral switching method, comprising the following steps:

[0008] Step 1: Obtain a stimulus-responsive polymer as a processing material;

[0009] Among them, the stimulus-responsive polymer is a pH-responsive polymer material or a photo-thermal-responsive polymer material;

[0010] Step 2: Place the stimulus-responsive polymer on a processing substrate to form a processing surface, and process a microstructure on the processing surface by using a femtosecond laser;

[0011] Among them, the microstructure is an array composed of M columns, and the M columns are uniformly distributed around the center of the array; M≥2;

[0012] The axis of the m-th column is connected to the center of the array by line A. m The outer side of the m-th column is divided into two regions C along the column axis. m and D m C m The crosslinking density is higher than D m Crosslinking density, C m D m The boundary line forms plane B m A m With B m Parallel; m∈[1,M];

[0013] If the m-th pillar is rotated around the center of the array to the position of the n-th pillar, the m-th pillar and the n-th pillar will completely overlap; n∈[1,M], m≠n;

[0014] Step 3: The processed surface is developed to obtain the developed microstructure;

[0015] Step four: The developed microstructure is placed in two different stimulus response environments. The capillary force generated by solution evaporation is used to complete the self-assembly of the microstructure. The reversibility of self-assembly and the anisotropy of the microstructure in different stimulus response environments are used to complete the chiral switching.

[0016] If the stimulus-responsive polymer is a pH-responsive polymer material, then the two different stimulus-responsive environments include acidic response solutions and alkaline response solutions.

[0017] If the stimulus-responsive polymer is a photothermal responsive polymer material, then the two different stimulus-responsive environments include a deionized water responsive solution under no light irradiation and a deionized water responsive solution under light irradiation.

[0018] The laser processing and chirality switching method for such chiral microstructures implements the methods or processes according to embodiments of this disclosure.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention uses femtosecond laser processing technology to process stimulus-responsive polymers, so that the processed columns have different crosslinking densities in the two lateral regions, thereby enabling the self-assembly of microstructures and reversible switching of chirality in different stimulus-responsive environments.

[0021] 2. The microstructure of the present invention is based on femtosecond laser processing, which can reduce the size to the submicron to 20-30 micrometer range. Attached Figure Description

[0022] Figure 1 Brief flow chart of the laser processing and chiral switching method of the switchable chiral microstructure proposed for the embodiment 1 of the present application;

[0023] Figure 2 Structural diagram of the photothermal responsive polymer material;

[0024] Figure 3 Figure 1 Top view of the two crosslinking density settings of the microstructure in the middle;

[0025] Figure 4 Figure 1 Process variation diagram of the self-assembly of adjacent pillars of the developed pillar group unit in the middle;

[0026] Figure 5 Figure 3 Variation diagram of the microstructure self-assembly and chiral switching of the developed pillar group unit in the middle under two different stimuli responsive environments;

[0027] Figure 6 Chiral electron microscope diagram finally presented by placing the developed pillar group unit in hydrochloric acid solution in the embodiment 2 of the present application;

[0028] Figure 7 Chiral electron microscope diagram finally presented by placing the developed pillar group unit in ammonia solution in the embodiment 2 of the present application;

[0029] Figure 8 State variation diagram of the developed pillar group unit placed in deionized water responsive solution under no light irradiation environment and deionized water responsive solution under light irradiation environment in the embodiment 3 of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0031] It should be noted that when a component is referred to as being “mounted on” another component, it can be directly on the other component or there can be a middle component. When a component is referred to as being “disposed on” another component, it can be directly disposed on the other component or there can be a middle component. When a component is referred to as being “fixed on” another component, it can be directly fixed on the other component or there can be a middle component.

[0032] ​​​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0033] Embodiment 1

[0034] Please refer to Figure 1 , Figure 1 The flow chart of the laser processing and chiral switching method for the switchable chiral microstructure provided in Embodiment 1 includes the following steps:

[0035] Step 1, obtaining a stimulus-responsive polymer as a processing material.

[0036] The stimulus-responsive polymer is a pH-responsive polymer material or a photothermal-responsive polymer material.

[0037] The stimulus-responsive polymer is a high-molecular responsive material, such as a hydrogel, a photoresist, etc.

[0038] For the pH-responsive polymer material, there are ion groups such as weakly basic or weakly acidic groups on the branched chain that can ionize. When the pH value of the environment changes to produce an internal and external concentration difference, the ion groups will swell or shrink by absorbing water, and the hydrogen bonds formed between the polymers will dissociate to cause a volume discontinuous swelling change.

[0039] For the photothermal-responsive polymer material, refer to Figure 2 The molecular network contains hydrophilic groups and hydrophobic groups. When the environment is illuminated, the molecular network will absorb light energy and convert it into heat energy, changing the temperature of the photothermal-responsive polymer material, and then changing the strength of the hydrogen bonds between the hydrophilic groups and the hydrophobic groups, to affect the water swelling amount of the photothermal-responsive polymer material, and realize the volume change.

[0040] Step 2, placing the stimulus-responsive polymer on a processing substrate to form a processing surface, and processing a microstructure on the processing surface using a femtosecond laser.

[0041] Generally, the processing substrate can be a glass slide or other element that can carry the stimulus-responsive polymer.

[0042] In this embodiment 1, a femtosecond laser two-photon processing platform is used to process the processing surface. The femtosecond laser two-photon processing platform is equipped with a femtosecond laser source, a sample stage, and a three-dimensional moving platform. Specifically, the femtosecond laser source uses a sapphire ultrafine oscillator; the sample stage is used to fix the processing substrate; and the three-dimensional moving platform is used to adjust the movement of the sample stage. In this way, by setting the laser processing parameters (such as laser power, structure parameters, structure ratio, etc.) and controlling the movement of the femtosecond laser along the set processing path, the microstructure can be processed on the processing surface.

[0043] The microstructure is an array of M columns, which are uniformly distributed around the center of the array, and M≥2. Specifically, the microstructure can be processed into a five-column array, or into a two-column array, a four-column array, an eight-column array, etc. according to needs. The size of the processed microstructure can reach the order of magnitude of sub-microns to two or three tens of microns. Of course, the column height can also be increased or decreased according to needs to control the size after subsequent self-assembly.

[0044] For the mth column, the outer side is divided into two regions C m and D m along the column axis. The exposure dose of C m is less than that of D m , so that different cross-linking densities are obtained in the two regions, that is, the cross-linking density of C m of the mth column is higher than that of D m ; m∈[1,M]. It should be noted that the exposure dose is controlled by the number of scans and the scan step distance in actual processing: more scans or smaller step distances can achieve a large exposure dose, and the region with a large exposure dose deforms less after being stimulated; on the contrary, the region with less laser scans or larger step distances has a small exposure dose, and the structure deforms greatly after being stimulated.

[0045] In addition, the area ratio of C m to D m is adjusted according to the selected material. In this embodiment 1, the area ratio of C m to D m is set to 1:3, which has been verified by subsequent experiments to obtain better deformation results when the selected material is a hydrogel.

[0046] Wherein, the axis of the mth column and the center of the array form a line A m ; the intersection line of C m and D m forms a plane B m ; A m is parallel to B m . Referring to Figure 3 , when M is 5, a top view of a five-column array is shown. Taking the column located at the bottom as an example,Figure 3 (a) shows C m located in D m the left side, Figure 3 (b) shows C m located in D m the right side.

[0047] It should be noted that the M pillars can be regarded as the mth pillar rotating around the array center at an equal angle of 360° / M for M-1 times. Therefore, if the mth pillar is rotated around the array center to the position of the nth pillar, the mth pillar is completely coincident with the nth pillar; n∈[1, M], m≠n.

[0048] Because of the different crosslinking densities of the two regions on the side of the pillar, different degrees of swelling deformation will occur in the same stimulus-responsive environment, so that the pillar bends to the side with a smaller swelling deformation. Generally, the crosslinking density ratio of C m and D m is 7:3, because it is found through experiments that the largest deformation of the pillar can be obtained under this ratio. Of course, the crosslinking density ratio of C m and D m may also be adjusted to other values, but the deformation is not as large as 7:3.

[0049] Step three, developing the processed surface to obtain the developed microstructure.

[0050] This step is to remove the excess stimulus-responsive polymer and only leave the required microstructure. Specifically, the processed surface is placed in a developing solution to remove the material outside the microstructure, i.e., the excess stimulus-responsive polymer:

[0051] If the stimulus-responsive polymer is positive, the stimulus-responsive polymer in the exposed area is removed and only the non-exposed area is retained. Generally, if the stimulus-responsive polymer is positive, the developing solution is a strong alkali solution diluted with water.

[0052] If the stimulus-responsive polymer is negative, the stimulus-responsive polymer in the non-exposed area is removed and only the exposed area is retained. Generally, if the stimulus-responsive polymer is negative, the developing solution is an ethanol developing solution.

[0053] Step four, the developed microstructure is placed in two different stimulus-responsive environments in sequence, and the self-assembly of the microstructure is completed by using the capillary force generated by the evaporation of the solution, and the chiral switching is completed by using the reversibility of self-assembly and the anisotropy of the microstructure in different stimulus-responsive environments (i.e., different swelling conditions). For different stimulus-responsive polymers, different stimulus-responsive environments are used:

[0054] Wherein, if the stimulus-responsive polymer is a pH-responsive polymer material, the two different stimulus-responsive environments include an acidic response solution and an alkaline response solution. If the stimulus-responsive polymer is a photothermal-responsive polymer material, the two different stimulus-responsive environments include a deionized water response solution in the absence of light irradiation and a deionized water response solution in the presence of light irradiation.

[0055] Specifically, the developed microstructure is first immersed in a solution of the first stimulus-responsive environment, and the solution of the first stimulus-responsive environment is evaporated until the liquid surface is gradually lower than the microstructure and completely evaporates. The pillars in the microstructure appear chiral bending and bending towards the center of the array, and are further adhesively assembled together and exhibit a first chirality.

[0056] Then the microstructure with the first chirality is immersed in a solution of the second stimulus-responsive environment, and the solution of the second stimulus-responsive environment is evaporated until the liquid surface is gradually lower than the microstructure and completely evaporates. The pillars in the microstructure appear chiral bending in the opposite direction to that in the first stimulus-responsive environment and bending towards the center of the array, and are further adhesively assembled together and exhibit a second chirality opposite to the first chirality.

[0057] It should be noted that the direction of the chiral bending appearing in the above process is related to the expansion amount of the two regions outside the pillar: for the mth pillar, when C m The expansion deformation is greater than D m The expansion deformation is greater than D m The expansion deformation is greater than D m The expansion deformation is less than D m The expansion deformation is less than D m The expansion deformation is less than D

[0058] Since the pillars are placed in the solution, the expansion amount is also related to the material of the pillar itself and the type of solution:

[0059] The acidic response solution is used to provide a low-pH stimulus-responsive environment, and the alkaline response solution is used to provide a high-pH stimulus-responsive environment.

[0060] If the stimulus-responsive polymer is an anionic pH-responsive polymer material, when the pH of the stimulus-responsive environment is less than the critical pH of the pillar deformation, the mth pillar produces chiral bending to the D m side; when the pH of the stimulus-responsive environment is greater than the critical pH of the pillar deformation, the mth pillar produces chiral bending to the C m side;

[0061] If the stimulus-responsive polymer is a cationic pH-responsive polymer material, when the pH of the stimulus-responsive environment is less than the critical pH of the pillar deformation, the mth pillar produces chiral bending to the C ma chiral bend is generated to the side; when the stimulus-responsive environment pH is greater than the pillar deformation critical pH, the mth pillar bends to D m a chiral bend is generated to the side.

[0062] The deionized water responsive solution in the light irradiation environment is used to provide a low temperature value of the stimulus-responsive environment; the deionized water responsive solution in the light irradiation environment is used to provide a high temperature value of the stimulus-responsive environment;

[0063] If the stimulus-responsive polymer is a negative reaction photo-thermal responsive polymer material, when the stimulus-responsive environment temperature is lower than the pillar deformation critical temperature, the mth pillar bends to C m a chiral bend is generated to the side; when the stimulus-responsive environment temperature is higher than the pillar deformation critical temperature, the mth pillar bends to D m a chiral bend is generated to the side.

[0064] If the stimulus-responsive polymer is a positive reaction photo-thermal responsive polymer material, when the stimulus-responsive environment temperature is lower than the pillar deformation critical temperature, the mth pillar bends to D m a chiral bend is generated to the side; when the stimulus-responsive environment temperature is higher than the pillar deformation critical temperature, the mth pillar bends to C m a chiral bend is generated to the side.

[0065] Referring to Figure 4 The principle of microstructure self-assembly and chiral switching is described by taking a double pillar array as an example:

[0066] The double pillar array is immersed in a solution of a first stimulus-responsive environment, and the pillars swell by absorbing water; and because the swelling amounts of the two regions on the side of the pillars are different, a chiral bend is generated to the side of the pillar with the smaller swelling amount (not shown in the figure). Referring to Figure 4 the left part of FIG. 1, as the solution of the first stimulus-responsive environment evaporates, the liquid level gradually lowers below the microstructure, and a meniscus appears around the two pillars, at which time the two pillars are subjected to a capillary force F c generated by the meniscus and an elastic support force F s of the pillars themselves. Among them, F c causes the pillars to gather to the center of the array, and F s pushes the pillars outward. Because F c is greater than F s , the pillars bend to gather to the center of the array. When the solution of the first stimulus-responsive environment completely evaporates, the two pillars gather to the center of the array. Referring to Figure 4 the right part of FIG. 1, at this time, F c disappears, and a van der Waals force F v generated by the contact of the two pillars appears; among them, F v causes the two pillars to attract each other, and F s pushes the pillars outward. At this time, Fv greater than F s The stability of the assembly can be ensured.

[0067] Then, the whole microstructure with the first chirality is immersed in the solution of the second stimulus-responsive environment, F v decreases and disappears, the double-pillar array is disassembled and returns to the upright state; then, similarly to the above, the pillars still swell by absorbing water and produce a chiral bending to the side with a smaller swelling amount, but the direction of the chiral bending is opposite to that in the first stimulus-responsive environment. As the solution of the second stimulus-responsive environment evaporates, the liquid level gradually falls below the microstructure until complete evaporation, and the two pillars gather to the center of the array and exhibit the opposite second chirality.

[0068] Therefore, by changing different response solutions, the double-pillar array can be reassembled to form different chiralities, achieving free switching.

[0069] It should be noted that the reason for exhibiting chirality is that the two regions on the side of the pillar have different crosslinking densities. If the two regions on the side of the pillar have the same crosslinking density, the pillar will not exhibit chiral bending caused by different swelling amounts, but will still exhibit a bending towards the center of the array due to the action of F c , F s during the evaporation of the solution, and can still achieve self-assembly, but does not exhibit chirality.

[0070] In addition, referring to Figure 5 , a state diagram of the chirality switching of a four-pillar array is shown, i.e., the four pillars can switch between different chiralities under different conditions.

[0071] Example 2

[0072] This example 2 provides a specific example to verify one case of example 1:

[0073] The stimulus-responsive polymer uses a pH-responsive hydrogel (i.e., an anionic pH-responsive polymer material), and the two different stimulus-responsive environments include a hydrochloric acid solution (i.e., an acidic response solution) and an ammonia solution (i.e., a basic response solution).

[0074] Specifically:

[0075] First, the preparation of pH-responsive hydrogel: take a capacity appropriate brown bottle, 0.8 mL of acrylic acid, 1.6 g of N-isopropyl acrylamide, 0.15 g of polyvinyl pyrrolidone, 1 mL of ethyl lactate into the bottle, stirring to make it completely dissolved, to get mixed solution; again take 2.5 mL of mixed solution with 0.5 mL of dipentaerythritol hexa-acrylate, 0.5 mL of triethanolamine and 100 μL of 4,4'-bis(diethylamino) benzophenone (20 wt%) and N,N-dimethylformamide solution stirring; then add a small amount of rhodamine dyeing treatment, to get pH-responsive hydrogel, its main components include: acrylic acid, N-isopropyl acrylamide, polyvinyl pyrrolidone, ethyl lactate, polydipentaerythritol penta-acrylate, triethanolamine, 4,4'-bis(diethylamino) benzophenone, N,N-dimethylformamide.

[0076] It should be noted that the prepared hydrogel should be placed in yellow light conditions for storage and use, and the use time should be preferably not more than two months.

[0077] Then the femtosecond laser processing is carried out:

[0078] The glass slide is selected as the processing substrate and is placed in a methanol and 3-(methacryloyloxy) propyl trimethoxysilane treatment liquid reagent bottle with a ratio of 1:19 for at least 24 hours, so that the subsequent processed microstructure can be fixed on the substrate and will not be washed away with the unprocessed area during the development process.

[0079] Then the glass slide is immersed in an ethanol reagent bottle, and then placed in an ultrasonic cleaning machine for 3-5 min; after taking out, it is washed with deionized water and wiped with a dust-free paper towel to reduce the influence of dust particles and other impurities on the processed structure and facilitate observation.

[0080] The hydrogel is added dropwise on the glass slide by using a pipette, and the glass slide is fixed on the femtosecond laser two-photon processing platform. The laser energy is adjusted to 30 mW, and the three-dimensional coordinates generated by MATLAB are imported into the software control system to control the processing path, and a five-column array is processed. The column height is 20 μm, and the distance between each column and the rotation center of the unit body is 4 μm.

[0081] Referring to Figure 6 A plurality of five-column arrays are processed on the processing surface, and the crosslinking density distribution of each five-column array is the same, which adopts the distribution of Figure 3 (b).

[0082] Taking any one five-column array as an example, as shown in Figure 3 (b). Figure 3(b) The lowermost column in (b) is taken as an example. From the top view, the left side of the column is the side with lower crosslinking density (processed using a 350 nm scan pitch), and the right side is the side with higher crosslinking density (processed using a 150 nm scan pitch), so that the crosslinking density ratio of the two sides is 3:7.

[0083] Then, the development process is carried out: the slide is reversely placed in the ethanol solution using the clamping device, so that the five-column array is immersed in the ethanol solution, and the un-solidified hydrogel is removed to obtain the desired five-column array.

[0084] Next, the five-column array is sequentially self-assembled in the hydrochloric acid solution and the ammonia solution:

[0085] At room temperature, the five-column array is placed in the hydrochloric acid solution, and the columns swell by absorbing water. The right side of the lowermost column in (b) is taken as an example. Since the pH of the hydrochloric acid solution is less than the pH required for the column deformation, the right side of the column swells more than the left side. The column bends to the left and is gathered to the center of the array during the evaporation process driven by capillary force. Figure 3 Figure 3 The other columns in (b) are similar to the lowermost column, and will not be repeated. After the hydrochloric acid solution is completely evaporated, the five columns are self-assembled and exhibit right-handed chirality, as shown in (c). Figure 6

[0086] The five-column array exhibiting right-handed chirality is placed in the ammonia solution, and the columns are restored to the standing state from the left-bent state. The columns still swell by absorbing water. The right side of the lowermost column in (b) is taken as an example. Since the pH of the ammonia solution is greater than the pH required for the column deformation, the right side of the column swells less than the left side. The column bends to the right and is gathered to the center of the array during the evaporation process driven by capillary force. Figure 3 Figure 3 The other columns in (b) are similar to the lowermost column, and will not be repeated. After the ammonia solution is completely evaporated, the five columns are self-assembled and exhibit left-handed chirality, as shown in (d). Figure 7

[0087] In this way, self-assembly in two environments and chirality transformation from right-handed in an acidic environment to left-handed in an alkaline environment are achieved.

[0088] Example 3

[0089] This example 3 provides a specific example to verify another case of example 1:

[0090] ​​​​The stimulus-responsive polymer adopts a photo-thermal hydrogel (i.e. a photo-thermal responsive polymer material with a negative response), and two different stimulus-responsive environments include a deionized water response solution in the absence of light irradiation and a deionized water response solution in the presence of light irradiation.

[0091] Specifically,

[0092] First, the photo-thermal hydrogel is prepared: take a brown bottle with an appropriate capacity, accurately weigh 400 mg of NIPAM, 30 mg of acrylamide, and 30 mg of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide in sequence and add them to the bottle, then use a pipette to extract 450 μL of ethylene glycol solution and add it to the bottle; then ultrasonically dissolve it in a 50℃ water bath for 20 min. After complete dissolution, a small amount of rhodamine dye is added for treatment to obtain a photo-thermal hydrogel. The main components of the photo-thermal hydrogel include: N-isopropyl acrylamide, acrylamide, diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, polyvinylpyrrolidone K30, and ethylene glycol.

[0093] It should be noted that the prepared hydrogel should be stored and used under yellow light conditions, and the use time should not exceed two months.

[0094] Then, femtosecond laser processing is performed:

[0095] The glass slide is selected as the processing substrate and is placed in a methanol and 3-(methacryloyloxy) propyl trimethoxysilane treatment liquid reagent bottle with a ratio of 1:19 for at least 24 hours to ensure that the microstructure can be fixed on the substrate during subsequent processing and will not be washed away with the unprocessed area during development.

[0096] Then, the glass slide is immersed in an ethanol reagent bottle, and then placed in an ultrasonic cleaning machine for 3-5 min; after taking it out, it is washed with deionized water, and then wiped clean with a dust-free paper towel to reduce the influence of dust particles and other impurities on the processed structure and facilitate observation.

[0097] The hydrogel is added to the glass slide using a pipette, and heated on a hot plate at 90℃ for 5 min. Then, the glass slide is fixed on the femtosecond laser two-photon processing platform, the laser energy is adjusted to 60 mW, and the three-dimensional coordinates generated by MATLAB are imported into the software control system to control the processing path, and a five-pillar array is processed. Among them, the pillar height is 20 μm, and each pillar is 4 μm away from the center of rotation of the unit.

[0098] Referring to Figure 8 A 4*4 group of five-pillar arrays are processed on the processing surface. Among them, the outer sides of the 12 groups of five-pillar arrays located in the outermost circle are processed with the same cross-linking density. For the 4 groups of five-pillar arrays located in the inner part, the left upper and right lower 2 groups are processed with different cross-linking densities. Figure 3The cross-linking density distribution of (a) is shown in the lower left and upper right two groups Figure 3 The cross-linking density distribution of (b) is shown in the lower left and upper right two groups

[0099] Then, the development process is carried out: the glass slide is reversely placed in the ethanol solution using the clamping device, and the five post arrays are immersed in the ethanol solution, so as to remove the un-solidified hydrogel, and the required five post arrays are obtained.

[0100] Next, the five post arrays are sequentially self-assembled in the deionized water response solution in the light-free environment and in the deionized water response solution in the light environment:

[0101] In the light-free environment, the deionized water solution at 20°C is added dropwise to the processing surface, and the posts swell by absorbing water. As the solution evaporates, the 12 groups of five post arrays in the outermost circle only appear to be curved towards the center of the array, and the 4 groups of five post arrays in the inner part, the upper left and lower right two groups appear to be chiral curved to the left, and curved towards the center of the array; the lower left and upper right two groups appear to be chiral curved to the right, and curved towards the center of the array. When the solution evaporates completely, refer to Figure 8 (a), the 16 groups of five post arrays are all self-assembled: the 12 groups of five post arrays in the outermost circle present simple achiral assembly; in the 4 groups of five post arrays in the inner part, the upper left and lower right two groups present right-handed chiral assembly, and the lower right and upper left two groups present left-handed chiral assembly.

[0102] The laser with a power of 100 mW is irradiated to the processing surface again, and the focal point of the laser is moved to the center of the 4*4 group of five post arrays, that is, the center of the 4 groups of five post arrays in the inner part. Since the laser increases the temperature of the solution near the focal point, the 4 groups of five post arrays in the inner part are equivalent to being heated because they are relatively close to the focal point of the laser. In this way, as the solution evaporates, the 12 groups of five post arrays in the outermost circle only appear to be curved towards the center of the array, and the 4 groups of five post arrays in the inner part, the upper left and lower right two groups appear to be chiral curved to the right, and curved towards the center of the array; the lower left and upper right two groups appear to be chiral curved to the left, and curved towards the center of the array. When the solution evaporates completely, refer to Figure 8 (b), the 16 groups of five post arrays are all self-assembled: the 12 groups of five post arrays in the outermost circle present simple achiral assembly; in the 4 groups of five post arrays in the inner part, the upper left and lower right two groups present left-handed chiral assembly, and the lower right and upper left two groups present right-handed chiral assembly.

[0103] Of course, a light-gathering disc can also be processed in advance at the center of the 4*4 group of five post arrays, so as to increase the light-heat conversion efficiency of the laser and increase the temperature rise of the solution near the focal point, so that the difference in chirality change is more obvious.

[0104] In this way, self-assembly in both environments is achieved, as well as a change in chirality from the non-illuminated environment to the illuminated environment.

[0105] The technical features of the above embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combinations of the technical features do not contradict each other, they should be considered as falling within the scope of the present disclosure.

[0106] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but should not be understood as a limitation on the scope of the patent. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all fall within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method of laser processing and switching of chiral microstructures, characterized in that, The method comprises the following steps: Step 1: obtaining a stimulus-responsive polymer as a processing material; The stimulus-responsive polymer is a pH-responsive polymer material or a photothermal-responsive polymer material; Step 2: placing the stimulus-responsive polymer on a processing substrate to form a processing surface, and processing a microstructure on the processing surface by using a femtosecond laser; The microstructure is an array of M columns, and the M columns are uniformly distributed around the center of the array; M≥2; A line A is formed between the center of the array and the center of the mth column m ; the outside of the mth column is divided into two regions C and D along the column axis m m , the cross-linking density of C m is higher than that of D m , the intersection line of C m , D m forms a plane B m ; A m is parallel to B m ; m ∈ [1, M]​ If the mth column is rotated to the position of the nth column around the center of the array, the mth column is completely coincident with the nth column; n∈[1,M], m≠n; Step 3: developing the processing surface to obtain a developed microstructure; Step 4: placing the developed microstructure in two different stimulus-responsive environments in sequence, using capillary force generated by solution evaporation to complete self-assembly of the microstructure, and using reversibility of the self-assembly and anisotropy of the microstructure in different stimulus-responsive environments to complete chiral switching; If the stimulus-responsive polymer is a pH-responsive polymer material, the two different stimulus-responsive environments include an acidic response solution and an alkaline response solution; If the stimulus-responsive polymer is a photothermal-responsive polymer material, the two different stimulus-responsive environments include a deionized water response solution in a light-free environment and a deionized water response solution in a light irradiation environment; In step 4, the developed microstructure is first immersed in a solution of the first stimulus-responsive environment, the solution of the first stimulus-responsive environment is evaporated, the liquid surface gradually lowers below the microstructure until complete evaporation, the columns in the microstructure appear chiral bending and bending towards the center of the array, and then are adhesively assembled together and exhibit a first chirality; then the microstructure with the first chirality is immersed in a solution of the second stimulus-responsive environment, the solution of the second stimulus-responsive environment is evaporated, the liquid surface gradually lowers below the microstructure until complete evaporation, the columns in the microstructure appear chiral bending in the opposite direction to that in the first stimulus-responsive environment and bending towards the center of the array, and then are adhesively assembled together and exhibit a second chirality opposite to the first chirality.

2. The method of claim 1, wherein the laser processing and chiral switching of the switchable chiral microstructure is performed by a laser. In step 1, the stimulus-responsive polymer is a high-molecular responsive material.

3. The method of claim 1, wherein the laser processing and chiral switching of the switchable chiral microstructure is performed by a laser. In step 2, a femtosecond laser two-photon processing platform is used to process the processing surface; wherein, for the mthpost, the exposure dose to C m is less than the exposure dose to D m .

4. The laser processing of microstructures and chiral switching method according to claim 2 or 3, wherein For the mth pillar, C m and D m The crosslinking density ratio is 7:

3. 5.The laser processing of microstructure and chiral switching method according to claim 2, wherein, In step 2, the microstructure is a five-column array. 6.The laser processing of micro-structures and chiral switching method according to claim 2, wherein, In step 3, the processing surface is developed in a developing solution to remove excess stimulus-responsive polymer; If the stimulus-responsive polymer is positive, the stimulus-responsive polymer in the exposed area is removed and only the non-exposed area is retained; If the stimulus-responsive polymer is negative, the stimulus-responsive polymer in the non-exposed area is removed and only the exposed area is retained. 7.The laser processing of micro-structures and chiral switching method according to claim 1, wherein, For the mth column, when C m swells by more than D m swells, the column develops a chiral bend to the D m side; when C m swells by less than D m swells, the column develops a chiral bend to the C m side.

8. The laser processing of microstructures and chiral switching method according to claim 1 or 6, wherein, In step 4, If the stimuli-responsive polymer is an anionic pH-responsive polymer material, when the stimuli-responsive environmental pH is less than the pillar deformation critical pH, the mth pillar generates a chiral bend towards D m ; when the stimuli-responsive environmental pH is greater than the pillar deformation critical pH, the mth pillar generates a chiral bend towards C m . If the stimuli-responsive polymer is a cationic pH-responsive polymer material, when the stimuli-responsive environmental pH is less than the pillar deformation critical pH, the mth pillar generates a chiral bend to the C m side; when the stimuli-responsive environmental pH is greater than the pillar deformation critical pH, the mth pillar generates a chiral bend to the D m side.

9. The laser processing of microstructures and chiral switching method according to claim 1 or 6, wherein, In step 4, If the stimulus-responsive polymer is a negative responsive photothermal-responsive polymer material, when the stimulus-responsive environmental temperature is lower than the column deformation critical temperature, the mth column generates a chiral bend to the C m side; when the stimulus-responsive environmental temperature is higher than the column deformation critical temperature, the mth column generates a chiral bend to the D m side; If the stimuli-responsive polymer is a positive-responding photothermal-responsive polymer material, when the stimuli-responsive environmental temperature is lower than the column deformation critical temperature, the mth column generates a chiral bend to the D m side; when the stimuli-responsive environmental temperature is higher than the column deformation critical temperature, the mth column generates a chiral bend to the C m side.

Images