Preparation method and application of PDMS photoresist based on femtosecond laser two-photon polymerization

Abstract

The application discloses a preparation method and application of PDMS photoresist based on femtosecond laser two-photon polymerization, and verifies the feasibility of the photoresist formula through micro-nano structure processing. The preparation of the photoresist is achieved by dissolving isopropyl-9H-thioxanthone-9-ketone and 2-isopropyl thioxanthone in tetrahydrofuran to form a photo initiator solution. Then, the PDMS prepolymer is mixed with the photo initiator solution, and stirring is carried out in the dark for 12 hours to ensure uniformity, and bubbles are removed through evaporation of THF and ultrasonic treatment, and finally high-quality PDMS photoresist is obtained. Through accurate control of the ratio of the photo initiator and the PDMS, the photosensitivity and processing performance of the photoresist are significantly improved. Combined with the femtosecond laser two-photon polymerization technology, high-resolution (submicron level) and three-dimensional complex structure micro-nano processing is realized, and the method is suitable for the fields of microfluidic chips, biomedical devices and optical devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new materials, in particular to a preparation method of PDMS photoresist based on femtosecond laser two-photon polymerization and application thereof. BACKGROUND

[0002] PDMS (Polydimethylsiloxane) is an organosilicon polymer composed of silicon (Si), oxygen (O), and carbon (C), with a chemical structure represented as (Si(CH3) 2O )n, where n is the number of repeating units. With the continuous development of micro-nano processing technology, femtosecond laser two-photon polymerization technology has gradually become an important tool in the field of micro-nano manufacturing due to its high resolution, three-dimensional processing capability, and the need for no mask. Polydimethylsiloxane (PDMS) is a material with excellent biocompatibility, flexibility, and optical transparency, which has been widely used in microfluidic chips, biomedical devices, and flexible electronic devices. However, traditional PDMS processing methods (such as thermal curing) have limitations in resolution, design freedom, and complex structure processing capability. Therefore, the present application proposes a PDMS photoresist preparation based on femtosecond laser two-photon polymerization, which realizes the rapid manufacturing of high-precision and complex three-dimensional structures through micro-nano structure processing verification. SUMMARY

[0003] Therefore, the present application provides a PDMS photoresist preparation based on femtosecond laser two-photon polymerization and verification feasibility through processing.

[0004] The present application provides a preparation method of PDMS photoresist based on femtosecond laser two-photon polymerization, including mixing two-photon initiators: isopropyl-9H-thioxanthone-9-ketone and 2-isopropyl thioxanthone ketone in a certain proportion.

[0005] Further, the method comprises the following steps:

[0006] Step S1, two-photon initiator preparation: mix isopropyl-9H-thioxanthone-9-ketone and 2-isopropyl thioxanthone ketone in a certain proportion in a solvent, stir and react under room temperature and light shielding, remove insoluble solids, and obtain a photo initiator of PDMS;

[0007] Step S2, preparation of photoresist: mix the two-photon initiator solution in step S1 and the PDMS prepolymer in a certain proportion, stir in the dark until uniform and bubble-free, and obtain a two-photon polymerization 3D printing photoresist; that is, the PDMS photoresist.

[0008] Further, the specific implementation of the step S1 is: taking the isopropyl-9H-thioxanthene-9-ketone and 2-isopropylthioxanthone, and the weight ratio of PDMS monomer is 0.6% and 0.4% respectively, then uniformly dissolving into tetrahydrofuran to obtain a photoinitiator solution.

[0009] Further, the specific implementation of the step S2 is: taking the PDMS pre-polymer and the dissolved photoinitiator solution, and then placing them into a magnetic stirrer for stirring for 12 hours, so that the photoinitiator and the pre-polymer PDMS are fully mixed and the tetrahydrofuran solution is evaporated, and then placing them into an ultrasonic cleaner to remove the steam pocket generated by the stirring of the PDMS, to obtain the PDMS photoresist.

[0010] The application provides the PDMS photoresist prepared by the above method, which contains one or more of silicon, oxygen, hydrogen or carbon elements, and the total mass fraction of the carbon element is not more than 20%; the PDMS photoresist exists in a liquid form and can be converted into a solid or gel state through a solidification reaction.

[0011] The application also provides the application of the PDMS photoresist, and a complex micro-nano structure can be processed; the application comprises the following steps: femtosecond laser processing: printing a complex microstructure on the PDMS photoresist; developing: developing and air-drying to obtain a polymerized structure. The developing verifies the feasibility of the application.

[0012] Further, the specific implementation of the femtosecond laser processing of the PDMS photoresist is: dropping the prepared PDMS photoresist into a pre-processed dust-free glass slide by using a pipette; placing the sample on a sample table of a femtosecond laser device, keeping the processing surface upward and perpendicular to the laser, and performing femtosecond laser processing. Selecting a structure to be processed, adjusting the processing layer number, scanning speed and point spacing of the structure through a special software.

[0013] Further, the processing environment of the femtosecond laser processing is an immersion lens oil with a refractive index of 1.5; the incident angle range of the femtosecond laser processing with the glass slide surface is 90°; the femtosecond laser processing has a laser pulse repetition frequency range of 80MHz, a center wavelength of 780±5nm, a pulse width of <120fs and a processing power of 40mW. The laser processing scanning speed is 1mm / s, and the scanning interval is 100nm; the scanning path of the femtosecond laser processing is a line segment reciprocating type layered scanning, that is, scanning the contour first, and then filling the layered scanning in the middle line segment; the femtosecond laser processing has a processing repetition number of 2 times.

[0014] Further, the specific implementation of the developing is: immersing the processed sample in an ethyl acetate solution for 2 minutes, cleaning the unhardened PDMS photoresist, so that the processed structure is retained on the glass sheet, and placing the glass sheet in a dust-free environment for 5 minutes to allow the ethyl acetate solution to volatilize naturally. Beneficial effects

[0015] (1) Ultra-high resolution: Two-photon polymerization can achieve sub-micron (even nanometer) resolution, much higher than the processing precision of traditional thermal curing PDMS.

[0016] (2) Three-dimensional processing capability: By precisely controlling the movement of the laser focus in three-dimensional space, complex three-dimensional micro-nano structures can be manufactured.

[0017] (3) No need for mold: Directly through computer control laser scanning path can realize the processing of complex structure, is a kind of maskless, moldless processing technology, and traditional thermal curing PDMS needs to make a mold in advance.

[0018] (4) High design freedom: Laser scanning path is completely controlled by computer, can easily manufacture highly complex three-dimensional structure, design flexibility is high, and traditional thermal curing PDMS is limited by the complexity and manufacturing difficulty of the mold.

[0019] The core of the present application is to mix two kinds of photoinitiators (isopropyl-9H-thioxanthone-9-ketone and 2-isopropyl thioxanthone) according to a certain proportion and then uniformly disperse them into PDMS, which can realize the processing of only through the interaction of laser and prepared PDMS photoresist, directly in the PDMS material inside the three-dimensional structure processing, without layering or mask, can manufacture complex three-dimensional micro-nano structure. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the processing device of the present application;

[0021] Figure 2 is a schematic diagram of the working process of the present application;

[0022] Figure 3 is a structure diagram of the present application;

[0023] Figure 4 is a structure diagram of the present application. DETAILED DESCRIPTION

[0024] The present application will be described in detail below in conjunction with the embodiments and drawings, but the present application is not limited to this.

[0025] Example 1: Glue preparation

[0026] This embodiment relates to a method for preparing PDMS photoresist based on femtosecond laser (two-photon absorption), as shown in Figure 2 , comprising the following steps:

[0027] Preparation of photo initiator: take isopropyl-9H-thioxanthone-9-ketone and 2-isopropyl thioxanthone, the weight ratio of PDMS monomer is 0.6% and 0.4% respectively, dissolve in 400ml of tetrahydrofuran, stir uniformly, remove bubbles, get the photo initiator solution;

[0028] Preparation of photoresist: take 1g of PDMS prepolymer and mix with the dissolved photo initiator solution, then put it into a magnetic stirrer to stir for 12 hours in the dark, so that the photo initiator and PDMS are fully mixed and uniform, then open the bottle cap and continue to stir to evaporate the tetrahydrofuran solution, finally put it into an ultrasonic cleaner to ultrasonic for 15 minutes to remove the steam pocket generated by stirring, after the system is uniform and bubble-free, the final photoresist is obtained;

[0029] Example two structure processing

[0030] This example relates to the processing of the PDMS photoresist of the application based on femtosecond laser two-photon polymerization, which includes:

[0031] As shown in Figure 1 The excitation light path of the photoresist generating two-photon polymerization is sequentially provided with a femtosecond laser, a beam turning mirror, a high-speed optical switch, an energy adjuster, a laser beam expander lens, a scanning galvanometer, a 4F optical system, a CCD, an objective lens, and a displacement stage.

[0032] Making a glass slide: soak the glass slide in deionized water, put it into an ultrasonic cleaner to clean the surface contaminants for 5 minutes; then use a cotton ball soaked in anhydrous ethanol to wipe the front and back of the glass slide, replace it with a cotton ball soaked in acetone to wipe the front and back of the glass slide; again use a cotton ball soaked in anhydrous ethanol to wipe the front and back of the glass slide, then rinse the glass slide with anhydrous ethanol, replace it with deionized water, dry the glass slide on a heating table at 90℃, use an oil-based pen to leave a cross mark on the glass slide and bake it dry, the processing of the glass slide is completed.

[0033] Making a processed sample: take a small amount of prepared PDMS photoresist with a pipette, drop it in the middle of the cross on the glass slide, then put it into a glass culture dish, put it into an oven at 90℃ and bake for 15 minutes to completely remove the tetrahydrofuran in the photoresist and make the photoresist disperse on the glass slide.

[0034] The excitation light path of the photoresist generating two-photon polymerization is shown in Figure 1

[0035] The excitation light path of the photoresist generating two-photon polymerization is sequentially provided with a femtosecond laser with a wavelength of 780nm, a beam turning mirror, a high-speed optical switch, an energy adjuster, a laser beam expander lens, a scanning galvanometer, a 4F optical system, a beam turning mirror, a CCD, an objective lens, and a displacement stage.

[0036] ​Processing preparation: drop objective oil on the objective, and place the prepared processing sample on the sample holder of the high-precision piezoelectric displacement table;

[0037] Processing file setting: draw the processing structure by using 3DMax, save the file in STL format, import the file into the maleon data process software, set the scanning speed, scanning step length, exposure time and other parameters of the processing structure, and generate the point cloud file required for processing;

[0038] Structure processing: select the point cloud file of the required processing structure in the processing system, import it into the processing control software MaleonFab, and the desired PDMS material micro-nano structure can be processed;

[0039] Developing: immerse the processed sample in ethyl acetate solution for 2 minutes, clean the uncured PDMS photoresist, and place it in a dust-free environment for 5 minutes to allow the ethyl acetate solution to volatilize naturally, so that the processed structure is retained on the glass sheet. The glass sheet can be placed in an observation instrument to observe the processed structure as shown in Figure 3 ;

[0040] In summary, the present application proposes a PDMS photoresist preparation based on femtosecond laser two-photon polymerization and a feasible proof scheme of micro-nano structure processing. First, the photo initiator (isopropyl-9H-thioxanthene-9-ketone and 2-isopropyl thioxanthone) is dissolved in tetrahydrofuran, and mixed with the PDMS prepolymer to prepare a uniform PDMS photoresist. Subsequently, femtosecond laser two-photon polymerization technology is used to perform high-precision micro-nano structure processing on the object carrier. The low heat affected zone and local solidification characteristics of femtosecond laser make the processing process have small damage to the material, and have the advantages of ultra-high resolution (sub-micron level), true three-dimensional processing capability, no need for mask, non-contact processing, etc. It is especially suitable for manufacturing complex three-dimensional micro-nano structures, and is suitable for biomedical devices, microfluidic chips and optical devices. The present application provides an efficient and flexible solution for high-precision micro-nano manufacturing.

Claims

1. An application of PDMS photoresist based on femtosecond laser two-photon polymerization, characterized in that, The preparation method includes the following steps: Step S1, Preparation of two-photon initiator: Isopropyl-9H-thioxanthone and 2-isopropylthioxanthone are mixed in a solvent in a certain proportion and stirred under light at room temperature to remove insoluble solids and obtain the photoinitiator of PDMS. Step S2, Preparation of photoresist: The two-photon initiator solution and PDMS precursor from step S1 are mixed in proportion and stirred in the dark until uniform and free of bubbles to obtain the two-photon polymerization 3D printing photoresist; that is, the PDMS photoresist. The specific implementation method of step S1 is as follows: the weight ratio of isopropyl-9H-thioxanthone and 2-isopropylthioxanthone to PDMS monomers is 0.6% and 0.4% respectively, and then they are uniformly dissolved in tetrahydrofuran to obtain a photoinitiator solution; The PDMS photoresist can be used to fabricate complex micro- and nano-structures; the process includes the following steps: femtosecond laser processing: printing complex microstructures on the PDMS photoresist; development: performing development and air drying to obtain the polymerized structure.

2. The application of PDMS photoresist based on femtosecond laser two-photon polymerization as described in claim 1, characterized in that, The specific implementation of step S2 is as follows: after mixing the PDMS precursor with the dissolved photoinitiator solution, the mixture is placed in a magnetic stirrer and stirred for 12 hours to fully mix the photoinitiator and the PDMS precursor and evaporate the tetrahydrofuran solution. Then, the mixture is placed in an ultrasonic cleaner to ultrasonically remove the vapor generated by the stirring of the PDMS to obtain the PDMS photoresist.

3. The application of PDMS photoresist based on femtosecond laser two-photon polymerization as described in claim 1 or 2, characterized in that, The PDMS photoresist is composed of one or more elements selected from silicon, oxygen, hydrogen, or carbon, with the total mass fraction of carbon not exceeding 20%. The PDMS photoresist exists in liquid form and can be transformed into a solid or gel state through a curing reaction.

4. The application of PDMS photoresist based on femtosecond laser two-photon polymerization as described in claim 3, characterized in that, The specific implementation method of PDMS photoresist femtosecond laser processing is as follows: the prepared PDMS photoresist is dropped into a pre-treated dust-free glass substrate using a pipette; the sample is placed on the sample stage of the femtosecond laser equipment, keeping the processing surface upward and perpendicular to the laser, and femtosecond laser processing is performed. The structure to be processed is selected, and the number of processing layers, scanning speed and dot pitch of the structure are adjusted by special software.

5. The application of PDMS photoresist based on femtosecond laser two-photon polymerization as described in claim 4, characterized in that, The femtosecond laser processing is performed in an immersion oil with a refractive index of 1.

5. The angle between the incident angle and the glass substrate surface is within the range of 90°. The laser pulse repetition frequency range is 80MHz, the center wavelength is 780±5nm, the pulse width is <120fs, and the processing power is 40mW. The laser processing scanning speed is 1mm / s, and the scanning interval is 100nm. The scanning path of the femtosecond laser processing is a reciprocating layered scanning of line segments, first scanning the outline, and then filling the middle line segments in a layered scanning manner. The femtosecond laser processing is repeated twice.

6. The application of PDMS photoresist based on femtosecond laser two-photon polymerization as described in claim 5, characterized in that, The specific development method is as follows: the processed sample is immersed in ethyl acetate solution for 2 minutes to wash away the uncured PDMS photoresist, so that the processed structure is retained on the glass slide, and then placed in a dust-free environment for 5 minutes to allow the ethyl acetate solution to evaporate naturally.

Images