Flexible material internally containing graphene and method for inducing graphene in flexible material

Abstract

The invention discloses a flexible material internally containing graphene and a method for inducing graphene in the flexible material. The method comprises the following steps: carrying out surface pretreatment on the flexible material; focusing laser of a laser device into the flexible material to scan and induce the graphene; wherein the laser uses a high-power objective lens; the laser power ranges from 100 mW to 200 mW; the scanning speed is 1 to 5 mm / s; the repetition frequency of the laser ranges from 600 kHz to 1 MHz. The inherent problems of unstable structure, packaging and the like in the prior art are solved, and the excellent flexibility and bending resistance characteristics of the terahertz absorber have certain advancement in the research of the terahertz absorber.

Description

Technical Field

[0001] The present application relates to the technical field of flexible materials, and in particular to a flexible material containing graphene inside and a method for inducing graphene inside the flexible material. Background Art

[0002] Terahertz absorption devices have great application potential in military stealth, electromagnetic interference shielding and future 6G communication technology. However, the flexibility of traditional electronic devices based on metal conductive materials and rigid substrates limits their application scenarios.

[0003] As one of the frontier interdisciplinary disciplines, flexible electronic technology has the advantage of breaking through the bottleneck of traditional rigid electronic technology, attracting many scholars to invest in the research of related devices, and producing a large number of innovative applications with their own advantages, involving electronic skin, flexible display screens, robot perception and wearable medical monitoring equipment. Therefore, polydimethylsiloxane (PDMS), which has the advantages of flexibility, transparency and biocompatibility, has attracted widespread attention from scholars.

[0004] The low conductivity of the original PDMS means that when it is used to prepare flexible electronic devices, it is usually necessary to improve its conductivity through various physical and chemical methods, such as using photolithography, ultraviolet ozone irradiation, etc. to prepare patterns on the PDMS surface to improve its tactile sensing sensitivity, or by doping conductive materials such as silver nanoparticles, carbon nanotubes, graphene, etc. with PDMS to form a composite material to improve its conductivity. However, the former requires complex processes or sophisticated instruments, which increases costs while also providing very limited performance improvements. Although the latter can achieve better performance, the conductive materials used also have the problem of high costs, and it is impossible to achieve selective doping and patterning of conductive materials. The cumbersome material preparation and doping processes involved are not suitable for large-scale industrial production.

[0005] Compared with the traditional method of synthesizing graphene, which requires strict high temperature or complex chemical reaction process, laser induced graphene (LIG) can directly produce high-resolution and spatially selective conductive structures on polymer substrates. Laser induced graphene is different from the strictly single-layer or few-layer quasi-two-dimensional sp 2 It is not a carbon lattice material, but a three-dimensional porous nano-carbon material. Its principle is to use the thermal effect of the laser to break the chemical bonds of the carbon precursor and cause it to recombine to form a graphene structure. It has technical advantages such as non-contact, mask-free and eco-friendly.

[0006] At present, LIG ​​technology has been used to conveniently and quickly prepare various flexible sensor devices with excellent performance. However, in order to achieve high mechanical properties of the device, it is often necessary to prepare LIG on a PI substrate and then transfer it to a PDMS membrane. Therefore, there are still obvious deficiencies in the process.

[0007] In 2021, Shuichiro Hayashi and others used femtosecond lasers to directly prepare highly crystalline graphene on the surface of PDMS and prepared fingertip-sized piezoelectric sensors, optimizing the process of predecessors. However, the direct preparation of highly crystalline graphene on the surface of PDMS often has problems such as poor structural stability and easy oxidation, and further packaging processes are required to protect it. Summary of the invention

[0008] In order to solve the above-mentioned deficiencies in the art, the present application aims to provide a flexible material containing graphene inside and a method for inducing graphene inside the flexible material. The inherent problems of structural instability and packaging existing in the existing process are solved, and its excellent flexibility and anti-bending properties have certain advancement in the research of terahertz absorbers.

[0009] According to one aspect of the present application, a method for inducing graphene inside a flexible material is provided, comprising:

[0010] Surface preparation of flexible materials; and

[0011] The laser is focused into the flexible material to scan and induce graphene;

[0012] Wherein, the laser uses a high-power objective lens;

[0013] The laser power is: 100-200mW;

[0014] The scanning speed is: 1-5 mm / s;

[0015] The repetition frequency of the laser is 600kHz-1MHz.

[0016] According to some embodiments of the present application, the surface pretreatment includes: using a 99.5% ethanol solution to clean the film surface of the flexible material.

[0017] According to some embodiments of the present application, the flexible material is polydimethylsiloxane.

[0018] According to some embodiments of the present application, the high-power objective lens includes: high-power objective lenses of 20x, 50x, and 100x specifications; preferably 50x.

[0019] According to some embodiments of the present application, the laser power is: 200 mW.

[0020] According to some embodiments of the present application, the scanning speed is: 2 mm / s.

[0021] According to some embodiments of the present application, the repetition frequency of the laser is: 1 MHz.

[0022] According to some embodiments of the present application, the central wavelength of the laser is 1030 nm and the pulse width is 238 fs.

[0023] According to another aspect of the present application, there is also provided a flexible material containing graphene inside prepared by the above method, and application of the flexible material containing graphene inside in a broadband terahertz absorber.

[0024] Compared with the prior art, this application has at least the following beneficial effects:

[0025] The present application provides a method for inducing graphene inside a flexible material. By using a specific laser spot size and power, graphene is induced inside the flexible material, solving inherent problems such as structural instability and packaging in existing processes, improving its conductive performance while retaining the excellent flexibility and anti-bending properties of the flexible material itself. The performance of the broadband terahertz absorber prepared using the flexible material with internally induced graphene in the present application is significantly improved in terms of absorption bandwidth and absorption rate compared to the laser-induced graphene material currently prepared on the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of inducing graphene inside a flexible material and testing its performance according to an exemplary embodiment of the present application.

[0027] Figure 2 Figure 1 shows a sample of a LIG broadband terahertz absorber according to an exemplary embodiment of the present application (a), a cross-sectional SEM image of the sample (b), a surface SEM image of the LIG layer of the sample (c), and a Raman image of the sample (d).

[0028] Figure 3 Measured absorption intensity curve (a) of the exemplary embodiment of the present application, absorption intensity curve under large bending radius (b), absorption intensity curve after 2000 bends (c).

[0029] Figure 4 The absorber simulation model and the simulated absorption intensity curve of the exemplary embodiment of the present application are shown.

[0030] Figure 5 These are the actual pictures of the example embodiments and comparative examples of the present application, where (a) is the fragile phenomenon existing in the surface preparation technology, (b) is the bulging and discontinuity phenomenon, (c) is the burn-through phenomenon, and (d) is the actual picture of the ultra-wideband terahertz absorber prepared in the present application.

[0031] Figure 6 This is a schematic diagram of inducing graphene on the surface of a flexible material according to a comparative example of the present application.

[0032] Figure 7 This is a morphology diagram of the LIG flexible material of the comparative example of the present application.

[0033] Figure 8 This is the LIG Raman spectrum of the flexible material of the comparative example of the present application.

[0034] Fig. 9 This is a test chart of the absorption rate of the flexible material of the comparative example of the present application. DETAILED DESCRIPTION

[0035] The technical solution of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0036] It is particularly important to point out that similar substitutions and modifications made to the present application are obvious to those skilled in the art, and they are all deemed to be included in the present application. Relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application to implement and apply the technology of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments.

[0037] If no specific conditions are specified in this application, the preparation shall be carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, for which the manufacturers are not specified, are all conventional products that can be obtained commercially.

[0038] The application is described in detail below.

[0039] Explanation of terms: Polydimethylsiloxane (PDMS); Laser Induce Graphene (LIG); Femtosecond Laser Induce Graphene (FsLIG); Terahertz; Absorber; Scanning Electron Microscope (SEM); Transmission Electron Microscope (TEM).

[0040] First of all, at present, most of the preparation of flexible devices is realized on PI substrates (since the first preparation of laser-induced graphene on polymers was realized on PI substrates, it has many characteristics such as mature technology, low cost and excellent performance).

[0041] However, the PI material itself is only flexible but has poor mechanical properties and cannot meet the requirements of stretchable devices. Therefore, it is necessary to prepare LIG from the PI substrate and then transfer the LIG conductive structure to the PDMS film with good mechanical properties through a transfer process. However, there are few studies on directly preparing LIG on the PDMS surface and using it for flexible sensing. In addition, the LIG flexible devices prepared on the surface face problems such as poor structural stability and easy oxidation, which require further packaging technology.

[0042] However, higher laser power may cause the material to be burned through, so the processing inside PDMS needs to be carried out under power-limited conditions. Since the spot of a low numerical aperture objective is large and the laser energy density is relatively small, it is not easy to achieve internal material modification under power-limited conditions. At the same time, its smaller beam divergence means that the energy attenuation in the direction perpendicular to the laser processing plane is low, which can easily cause the laser to ablate the material surface in advance, making it difficult to achieve internal processing.

[0043] This application realizes the one-step preparation of LIG inside a transparent flexible material. By focusing a femtosecond laser beam inside a PDMS film, the material inside the flexible polymer can be modified, resulting in an instantaneous high temperature and high pressure state at the laser focus point inside, which causes the native bonds of PDMS to break and the carbon atoms to recombine, thereby achieving graphene. The process of processing LIG inside a transparent flexible material is further used to manufacture terahertz absorbers, achieving an absorbance of more than 90% within a wide frequency band of 0.5-4THz, and the absorption performance remains stable at a large bending radius and after 2000 bends. It not only solves the inherent problems of structural instability and packaging in existing processes, but its excellent flexibility and anti-bending properties are also advanced in the research of terahertz absorbers. Therefore, the direct preparation of LIG inside a transparent polymer is of great significance for the research and application of flexible devices.

[0044] Instruments and equipment:

[0045] High-power femtosecond fiber laser with a central wavelength of 1030nm (E-Power Technology)

[0046] Scanning electron microscope (SEM, Regulus8100, Hitachi, Japan)

[0047] THz-FDS transmission test module (Toptica terascan 1550, Munich, Germany)

[0048] 50x near-infrared objective lens with numerical aperture 0.65 (M Plan Apo NIR, Mitutoyo, Japan) Confocal Raman spectroscopy imaging instrument (532nm laser, Nanobase, Korea)

[0049] Electromagnetic solver (CST Microwave Studio 2018)

[0050] Example

[0051] Preparation of the flexible material containing graphene inside the present application:

[0052] The PDMS (Dow Corning DC184, USA) elastomer and curing agent were mixed thoroughly in a weight ratio of 10:1 and poured into a square mold for thermal curing at 70 °C for 2 h. Before the experiment, the film was cut into 40 × 30 mm 2 The film surface was cleaned with ethanol (99.5%).

[0053] A 50x near-infrared objective with a numerical aperture of 0.65 was used to focus the femtosecond laser beam inside a 1mm thick PDMS film. The laser parameters for processing were a repetition frequency of 1MHz, a power of 200mW, and a scanning speed of 2mm / s. It was observed that the structure of a single line processing presented a line structure with a width of 3μm. The scanning line spacing was set to 3μm, and a 10mm*10mm surface structure was processed.

[0054] Comparative Example 1 Graphene induced on the surface of flexible material

[0055] The PDMS (Dow Corning DC184, USA) elastomer and curing agent were thoroughly mixed in a weight ratio of 10:1 and poured into a square mold for thermal curing at 70°C for 2 h. Before the experiment, the film was cut into a rectangular structure of 40×30 mm2 and the film surface was cleaned with ethanol (99.5%).

[0056] A high-power femtosecond fiber laser with a central wavelength of 1030 nm (Eli Technology, China) was used. The laser parameters were selected as a repetition rate of 600 KHz-1 MHz, a scanning speed of 0.5 mm / s-5 mm / s, and a power of 200 mW-1 MW. A 10x near-infrared objective lens with a numerical aperture (NA) of 0.3 (M Plan Apo NIR, Mitutoyo, Japan) was used to focus the laser on the surface of the PDMS film for processing.

[0057] The flexible material of the surface-induced graphene prepared in this comparative example is Figure 5 As shown in a, it is easy to break.

[0058] Comparative Example 2

[0059] The preparation steps are the same as those in Example 1, except that the scanning speed is less than 1 mm / s.

[0060] The flexible material prepared in this comparative example has a bulging discontinuity phenomenon and cannot be used (such as Figure 5 b).

[0061] Comparative Example 3

[0062] The preparation steps are the same as those in Example 1, except that the power is greater than 200 mW.

[0063] The flexible material prepared in this comparative example will produce explosion points (i.e. burn-through or large bulge structure, such as Figure 5 c) cannot be used.

[0064] Comparative Example 4: Preparation of broadband terahertz absorber by inducing graphene on the surface of flexible material

[0065] Using CO on the surface of flexible polymer material polyimide (PI) film 2 Laser-induced graphene fabrication of terahertz absorbers.

[0066] The PI film with a thickness of 50 μm was attached to the Al substrate and a CO laser with a focal spot size of 50 μm and a wavelength of 10.6 μm was used. 2 The laser power can be continuously switched in the range of 0.01-30W, and the scanning speed of the laser can also be adjusted. The laser power is set to 40-80% of the maximum laser power, and the scanning speed is fixed at 230mm / s. The graphene grid is formed by directly scratching the PI film with the laser, such as Figure 6 As shown in a.

[0067] The absorber is removed from the aluminum substrate and consists of a two-layer structure, the top layer of grid graphene is made of PI film, and the bottom layer is the residual PI film, which supports the flexibility of the terahertz graphene grid absorber. By changing the processing parameters of graphene, its morphology and performance can be changed. Therefore, the incident terahertz wave is absorbed to different degrees, such as Figure 6 As shown in b.

[0068] The period P of the basic structural unit of the grid is designed to be 450 μm. By changing the laser parameters, the thickness and width of the graphene stripes can be changed, such as Figure 6 As shown in c.

[0069] Experimental Example Characterization and Performance Testing of the Flexible Materials in the Embodiments of the Application

[0070] 1. Characterization of the surface and cross-sectional morphology of FsLIG by scanning electron microscopy:

[0071] like Figure 2As shown in b, after multiple processing, a modified layer with a thickness of about 300 μm was obtained inside the PDMS.

[0072] like Figure 2 As shown in Figure c, by observing the internal LIG morphology through SEM, we can see that the surface presents a neatly arranged bulge structure. This is because the non-carbon material of PDMS is vaporized and expanded to form bulges after the thermal effect of the femtosecond laser, and the remaining carbon elements are reorganized to form graphite carbon. Since the thermal expansion of the graphite lattice is anisotropic, the structure is peeled off under strong heating to form graphene.

[0073] 2. Characterization of LIG production using confocal Raman spectroscopy imaging instrument:

[0074] like Figure 2 As shown in d, the Raman spectrum shows obvious graphene characteristic peaks, including the peak at 1350 cm -1 The characteristic peaks on the left and right are D bands, which originate from defects and edge functional groups; located at 1580cm -1 The characteristic peak nearby is the G band, which originates from the graphene sp 2 The main vibration mode of the domain; the 2D band is located at 2700cm -1 At, it is composed of graphite sp 2 The second-order vibration mode of the domains was generated, indicating the formation of LIG.

[0075] 3. Use THz-FDS transmission test module for device performance testing:

[0076] The broadband terahertz absorber consists of three parts: PDMS film, LIG ​​functional layer and bottom gold film. The LIG functional layer is located inside the PDMS film and plays a major role in absorbing terahertz waves.

[0077] The THz-FDS transmission test module is used to test the reflection spectrum of the device. It mainly consists of two distributed feedback (DFB) lasers, two fiber-coupled InGaAs optical mixers, dual-laser control intelligent electronic devices and a vertically arranged transmission test optical path.

[0078] The sample is placed on a movable base on the Z axis, and the base is moved to a height that allows the probe of the transmission test light path to be in close contact with the upper surface of the sample. All transmission spectra between 0THz-4THz are scanned at a step length of 50MHz, with an integration time of 30ms to obtain more accurate spectra. At this time, the instrument obtains the reflection spectrum of the device. Due to the presence of the gold film at the bottom of the device, the transmission intensity is basically zero, so the actual absorption intensity A can be calculated according to the formula A=1-|R| 2 Calculated, where R is the device reflection intensity.

[0079] Test results such as Figure 3As shown in a, a high terahertz absorption rate of more than 95% can be observed in a wide band of 0.5-4 THz. In addition, the absorption performance has almost no change after a large bending radius (7.32 mm) and 2000 bends (see Figure 2). Figure 3 b, as shown in 3c).

[0080] 4. Use electromagnetic solver for simulation verification:

[0081] The dielectric constant ε of PDMS material is 2.7, and the dielectric loss tangent is 0.001. The dielectric constant ε of LIG material is 2.4, and the dielectric loss tangent is 0.99.

[0082] The absorption intensity of the structure in the 0-2THz band is simulated, and the simulation results are as follows Figure 4 As shown, it can be observed that the simulated absorption rate of the device in the corresponding band oscillates slightly around 90%. Considering that the special porous honeycomb structure of actual LIG has strong scattering losses for terahertz waves, but the software level cannot simulate the micro-nano structure of the material, this can explain why the actual test structure has better performance than the simulation results.

[0083] Comparative Experimental Example Characterization and Performance Test of the Flexible Material of Comparative Example 4 of the Application

[0084] 1. Characterization of the surface and cross-sectional morphology of LIG by scanning electron microscopy:

[0085] like Figure 7 As shown in a, the surface morphology of LIG was observed using a scanning electron microscope, and the porous structure of graphene can be seen.

[0086] like Figure 7 As shown in b, the cross-sectional morphology of LIG was observed using a scanning electron microscope. Compared with LIG, the PI film is quite thin, indicating that most of the PI is converted into LIG.

[0087] 2. Characterization of LIG production using confocal Raman spectroscopy imaging instrument:

[0088] like Figure 8 As shown, the Raman spectra of LIG are at 1359, 1583 and 2713 cm -1 D, G, and 2D peaks are shown at , indicating that PI is converted into graphene under the laser processing parameters.

[0089] 3. Use THz-TDS transmission test module for device performance testing:

[0090] like Fig. 9As shown, the scanning speed is fixed at 230 mm / s, and when the laser processing power is 40%-80% of the maximum power, the absorbance can be widely adjusted in the range of 10%-90%. Taking the sample processed with a laser power of 80% of the maximum laser power as an example, its absorption rate reaches 90% in the range of 0.5-2.0 THz, but it is lower than the performance of the broadband terahertz absorber of the present application, and its performance in absorption bandwidth and absorption rate are lower than that of the present application.

[0091] The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A method for inducing graphene inside a flexible material, It is characterized in that include: Surface pretreatment of flexible materials; as well as The laser is focused into the flexible material to scan and induce graphene; Wherein, the laser uses a high-power objective lens; The laser power is: 100-200mW; The scanning speed is: 1-5 mm / s; The repetition frequency of the laser is 600kHz-1MHz.

2. The method according to claim 1, It is characterized in that The surface pretreatment includes: using 99.5% ethanol solution to clean the film surface of the flexible material.

3. The method according to claim 1, It is characterized in that The flexible material is polydimethylsiloxane.

4. The method according to claim 1, It is characterized in that The high-power objective lenses include: high-power objective lenses of 20x, 50x, and 100x specifications.

5. The method according to claim 4, It is characterized in that The laser power is: 200mW.

6. The method according to claim 5, It is characterized in that The scanning speed is: 2 mm / s.

7. The method according to claim 6, It is characterized in that The repetition frequency of the laser is: 1 MHz.

8. The method according to claim 7, It is characterized in that The central wavelength of the laser is 1030 nm and the pulse width is 238 fs.

9. A flexible material containing graphene inside prepared by the method according to any one of claims 1 to 8.

10. Use of the flexible material containing graphene inside as claimed in claim 9 in a broadband terahertz absorber.

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