Terahertz regulation and control conductive aerogel as well as preparation method and application thereof

Abstract

The invention discloses terahertz regulation and control conductive aerogel and a preparation method and application thereof.The preparation method comprises the following steps that mixed precursor dispersion liquid of cellulose nanofibers, sodium alginate and conductive filler is prepared; the mixed precursor dispersion liquid is poured into a mold, the mold is immersed into liquid nitrogen, temperature gradients in the vertical direction and the horizontal direction are formed in the mixed precursor dispersion liquid, bidirectional freezing is carried out, and growth of layered ice crystals in the parallel direction in the mixed precursor dispersion liquid is promoted; after bidirectional freezing is completed, freeze drying is conducted, and the product is obtained. The layered and high-porosity aerogel is assembled through a simple and convenient two-way freeze drying process, and the biopolymer aerogel has large-scale and parallel-oriented micron-sized pores and shows excellent mechanical strength, flexibility and elasticity. The conductivity of the aerogel can be changed by compressing the aerogel, so that the terahertz performance, including birefringence and absorption characteristics, of the aerogel can be intelligently regulated and controlled.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz-regulated aerogels, and particularly relates to a terahertz-regulated conductive aerogel and its preparation method and application. Background Art

[0002] The statements herein only provide background art related to the present invention and do not necessarily constitute prior art.

[0003] Terahertz (THz) radiation lies between infrared and microwave frequencies. It has a wide range of applications in communication, sensing, and medical imaging. When the terahertz parameters are regulated, the communication performance can be improved, such as achieving high transmission rates and enhancing signal quality, so as to meet the demand for instantaneous transmission of big data and improve the reliability and stability of the communication system. In addition, regulating the terahertz parameters can expand its application fields. For example, high-resolution imaging can be achieved in imaging technology, and high-sensitivity detection can be realized in security inspection and sensing fields. At the same time, the dynamic regulation ability enables terahertz devices to automatically adjust parameters according to environmental changes, improving the adaptability and flexibility of the system.

[0004] In the prior art, when regulating terahertz, inelastic materials are prone to irreversible deformation or damage when subjected to external forces, which will affect the stability and repeatability of the test. For example, in multiple tests or in a dynamic environment, inelastic materials may not be able to maintain consistent performance, while elastic materials can return to their original state to ensure the reliability of the test results. Secondly, when inelastic materials are mechanically deformed, their internal structure may change, resulting in unstable electromagnetic parameters (such as dielectric constant and loss factor) of the materials, which will affect the propagation characteristics of terahertz waves and thus the accuracy of the test results.

[0005] In addition, the optical parameters such as transmittance and reflectance of inelastic materials in the terahertz band may not be as stable as those of elastic materials, which will increase the uncertainty of the test. Finally, the performance of inelastic materials in extreme environments may not be as stable as that of elastic materials. For example, in environments with large temperature changes, low temperatures, or high humidity, the performance of inelastic materials may decrease significantly, affecting the applicable range of terahertz tests. Therefore, in terahertz test applications that require high stability and high precision, elastic materials usually have more advantages.

[0006] Aerogels have received extensive attention in the academic and industrial communities due to their light weight, porosity, designable microstructure, sustainability, and renewability. They can be combined with other nanomaterials with excellent electrical, thermal, and optical properties to form powerful structures, showing great potential in fields such as thermal insulation, energy storage, sensors, and electromagnetic wave absorption or shielding.

[0007] One of the challenges in using aerogels for conductive applications (such as in the terahertz frequency range) is integrating conductive fillers, such as carbon nanotubes, graphene, metal nanoparticles, etc., while maintaining the structural integrity and unique properties of the aerogel. If the conductive fillers are unevenly distributed, it is likely to cause discontinuity of the conductive network, thereby reducing the overall conductivity. For example, the aggregation of fillers will reduce their effective contact area with the matrix. In addition, adding conductive fillers may make the aerogel brittle, reducing its elasticity and toughness and affecting the service life of the aerogel. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a terahertz-regulated conductive aerogel, its preparation method and application.

[0009] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0010] In the first aspect, the present invention provides a preparation method of a terahertz-regulated conductive aerogel, including the following steps:

[0011] Prepare a mixed precursor dispersion of cellulose nanofibers (CNF), sodium alginate and conductive fillers;

[0012] Pour the mixed precursor dispersion into a mold and immerse the mold in liquid nitrogen to form a temperature gradient in the vertical and horizontal directions in the mixed precursor dispersion, perform bidirectional freezing, and promote the growth of parallel-layered ice crystals in the mixed precursor dispersion;

[0013] After the bidirectional freezing is completed, perform freeze-drying to obtain the product.

[0014] The mold is a stainless steel mold or a copper mold.

[0015] The present invention assembles a layered, highly porous aerogel through a simple bidirectional freeze-drying process. These biopolymer aerogels have large-scale, parallel-oriented micron-sized pores and exhibit excellent mechanical strength, flexibility and elasticity. By compressing the aerogel, its conductivity can be changed, thereby intelligently regulating its terahertz properties, including birefringence and absorption characteristics.

[0016] In some embodiments, in the mixed precursor dispersion, the concentration of cellulose nanofibers (CNF) is 1%-4%, the concentration of sodium alginate is 1%-4%, and the concentration of conductive fillers is 2%-20%, where % is mass percentage.

[0017] In some embodiments, the conductive filler is MXene, silver nanowires (AgNW) or carbon nanotubes (CNT).

[0018] Due to the incorporation of conductive fillers, the prepared conductive aerogel has advantages such as low density, high surface area, and strong conductivity, making it applicable to terahertz regulation.

[0019] When integrating conductive fillers such as MXene, AgNW, and CNT into the aerogel, strategies such as constructing a three-dimensional conductive network, optimizing filler dispersion, utilizing synergistic effects, controlling filler content and morphology, and using the ice crystal template method can be adopted to solve the problem of enhancing conductivity while maintaining the structural integrity and unique properties of the aerogel. For example, MXene can form a three-dimensional network by surface modification and curling into nanofibers, enhancing conductivity and mechanical properties; AgNW can improve dispersion and stability by compounding with CNF; CNT can precisely regulate its content and distribution through freeze-drying to achieve excellent conductivity and mechanical properties. These methods not only improve the conductivity of the aerogel but also further optimize its electromagnetic shielding and mechanical properties through synergistic effects and ordered structure design.

[0020] In some embodiments, the time for bidirectional freezing is 20 - 60 min.

[0021] In some embodiments, the temperature for freeze-drying is -80 to -60 °C, and the time for freeze-drying is 40 - 50 h.

[0022] In a second aspect, the present invention provides a terahertz-regulating conductive aerogel prepared by the above preparation method.

[0023] In a third aspect, the present invention provides the application of the conductive aerogel in the preparation of a terahertz antenna, a terahertz modulator, a terahertz imaging system, a terahertz filter, or a terahertz waveguide.

[0024] In a fourth aspect, the method for regulating terahertz using the conductive aerogel is as follows: Compress the prepared conductive aerogel to change its conductivity, and according to the change in conductivity, intelligently regulate the terahertz absorption and birefringence properties of the conductive aerogel.

[0025] The beneficial effects obtained from one or more of the above embodiments of the present invention are as follows:

[0026] The present invention assembles a layered and highly porous aerogel through a simple bidirectional freeze-drying process. These biopolymer aerogels have large-scale, parallel-oriented micron-sized pores, showing excellent mechanical strength, flexibility, and elasticity. By compressing the aerogel, its conductivity can be changed, thereby intelligently regulating its terahertz properties, including birefringence and absorption characteristics.

[0027] This method ensures the low density and porous structure of the aerogel while enhancing its electrical conductivity to effectively interact with terahertz waves. The aerogel prepared using this method can be used in terahertz devices, including sensors, filters, modulators, and imaging systems.

[0028] In addition, the present invention also provides a method for intelligently regulating the terahertz performance of the aerogel by changing its physical form, that is, by compressing the aerogel to change its electrical conductivity, thereby achieving dynamic regulation of its terahertz performance. Brief Description of the Drawings

[0029] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0030] Figure 1 are the physical picture (a) and scanning electron microscope (b) of the conductive aerogel prepared in Example 1 of the present invention;

[0031] Figure 2 is the terahertz wave absorption performance of the conductive aerogel prepared in Example 1;

[0032] Figure 3 is the terahertz birefringence performance of the conductive aerogel prepared in Example 1 under different compression ratios;

[0033] Figure 4 is the electrical conductivity of the conductive aerogel prepared in Example 1 under different compression ratios. Detailed Description of the Invention

[0034] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0035] Example 1

[0036] A preparation method of a terahertz-regulated conductive aerogel includes the following steps:

[0037] Using the TEMPO / NaBr / NaClO system, selectively oxidize the primary alcohol hydroxyl groups of cellulose to generate carboxyl groups to obtain a stable CNF (cellulose nanofiber) dispersion with a concentration of 2 wt%;

[0038] Dissolve sodium alginate in deionized water to obtain a stable SA dispersion with a concentration of 2 wt%;

[0039] Mix the CNF dispersion and the SA dispersion at a volume ratio of 3:2, then add the conductive filler MXene thereto, and adjust the concentration of the conductive filler MXene to 2 wt%, thus obtaining the mixed precursor dispersion;

[0040] Cast the MXene / CNF / SA precursor dispersion into a stainless-steel cold mold, and immerse the mold in liquid nitrogen for bidirectional freezing for 30 min;

[0041] After the bidirectional freezing is completed, freeze-dry at -80 °C and 5 Pa for 48 hours to obtain the product.

[0042] This setting generates vertical and horizontal temperature gradients, promoting the growth of large-scale, parallel-oriented layered ice crystals in the dispersion. As the ice crystals form, MXene / CNF / SA hybrid cell walls are formed within the frozen hydrogel.

[0043] Figure 1 Figure (a) and scanning electron microscope (b) of the conductive aerogel prepared in Example 1 of the present invention. Figure 1 It can be seen that an anisotropic elastic conductive aerogel is successfully prepared, and the spacing of the layered aerogel can be controlled within 20 - 50 μm.

[0044] The terahertz time-domain spectroscopy (TDS) test mainly includes steps such as experimental preparation, sample and reference signal acquisition, time-domain signal measurement, signal processing and spectral analysis, data analysis and result evaluation, and report recording.

[0045] First, ensure the stability of the experimental environment and calibrate the equipment;

[0046] Then, use a femtosecond laser to generate terahertz pulses, and collect the sample signal and the reference signal respectively. Scan the time-domain waveform by adjusting the optical delay line, and detect the terahertz electric field intensity using an electro-optic crystal or a photoconductive antenna.

[0047] Next, perform a Fourier transform on the time-domain signal, convert it to the frequency domain, and calculate parameters such as the absorption coefficient and refractive index of the sample.

[0048] Finally, process and analyze the spectral data, generate a detection report and save the record. This process realizes the non-destructive detection and quantitative analysis of the sample.

[0049] Due to its layered structure and elastic properties, the aerogel of the present invention can change its conductivity through external pressure such as compression, as Figure 2 ( Figure 2Among them, the compressive strains corresponding to different thicknesses are 46.2%, 30.8%, 15.4%, and 0% respectively. The channels parallel to the aerogel are denoted as 0°, and the channels perpendicular to the aerogel are denoted as 90°). As shown, this compression causes the rearrangement of the conductive fillers inside the aerogel, thereby changing the overall conductivity of the material. Since the terahertz performance is closely related to the conductivity, this change in conductivity directly affects the terahertz absorption and birefringence characteristics of the aerogel, enabling the terahertz performance of the aerogel to be intelligently regulated by external stimuli.

[0050] As Figure 3 ( Figure 3 Among them, 0%, 15.4%, 30.8%, and 46.2% are the compressive strain rates respectively) As shown, by precisely controlling the compression force and compression rate, the precise regulation of the terahertz performance of the aerogel can be achieved, making it adaptable in different application scenarios. For example, in a terahertz communication system, the conductivity of the aerogel can be adjusted to optimize the transmission and reception of signals; in a terahertz imaging system, the birefringence characteristics of the aerogel can be changed to control the resolution and contrast of the image, as Figure 4 shown.

[0051] Example 2

[0052] A preparation method of a terahertz-regulating conductive aerogel includes the following steps:

[0053] Using the TEMPO / NaBr / NaClO system, the primary alcohol hydroxyl groups of cellulose are selectively oxidized to generate carboxyl groups to obtain a stable CNF (cellulose nanofiber) dispersion with a concentration of 2 wt%;

[0054] Dissolve sodium alginate in deionized water to obtain a stable SA dispersion with a concentration of 2 wt%;

[0055] Mix the CNF dispersion and the SA dispersion in a volume ratio of 4:1, then add the conductive filler AgNW to it, and adjust the concentration of the conductive filler AgNW to 4 wt% to obtain a mixed precursor dispersion;

[0056] Pour the AgNW / CNF / SA precursor dispersion into a mold equipped with a stainless steel cold finger, and immerse the mold in liquid nitrogen for bidirectional freezing for 60 min;

[0057] After the bidirectional freezing is completed, freeze-dry at -80 °C and 5 Pa for 48 hours to obtain it.

[0058] This setting generates vertical and horizontal temperature gradients, promoting the growth of large-scale, parallel-directional layered ice crystals in the dispersion. As the ice crystals form, AgNW / CNF / SA hybrid cell walls are formed inside the frozen hydrogel.

[0059] Example 3

[0060] A preparation method of a terahertz-regulated conductive aerogel includes the following steps:

[0061] Using the TEMPO / NaBr / NaClO system, selectively oxidize the primary alcohol hydroxyl groups of cellulose to generate carboxyl groups to obtain a stable CNF (cellulose nanofiber) dispersion with a concentration of 2 wt%.

[0062] Dissolve sodium alginate in deionized water to obtain a stable SA dispersion with a concentration of 2 wt%.

[0063] Mix the CNF dispersion and the SA dispersion in a volume ratio of 1:4, then add the conductive filler CNT thereto, and adjust the concentration of the conductive filler CNT to 8 wt% to obtain a mixed precursor dispersion.

[0064] Cast the CNT / CNF / SA precursor dispersion into a mold equipped with a stainless-steel cold finger, and immerse the mold in liquid nitrogen for bidirectional freezing for 20 min.

[0065] This setting generates vertical and horizontal temperature gradients, promoting the growth of large-scale, parallel-oriented layered ice crystals in the dispersion. As the ice crystals form, CNT / CNF / SA hybrid cell walls are formed within the frozen hydrogel.

[0066] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing terahertz-controlled conductive aerogel, characterized in that: The method comprises the following steps: preparing a mixed precursor dispersion of cellulose nanofibers, sodium alginate and conductive filler; The mixed precursor dispersion is poured into a mold, and the mold is immersed in liquid nitrogen to form a temperature gradient in the vertical and horizontal directions in the mixed precursor dispersion, and bidirectional freezing is performed to promote the growth of lamellar ice crystals in parallel directions in the mixed precursor dispersion; After the two-way freezing is completed, freeze-drying is performed to obtain the product.

2. The method for preparing terahertz-controlled conductive aerogel according to claim 1, characterized in that: In the mixed precursor dispersion, the concentration of cellulose nanofibers is 1%-4%, where % is mass percentage.

3. The method for preparing terahertz-controlled conductive aerogel according to claim 1, characterized in that: In the mixed precursor dispersion, the mass percentage of the conductive filler is 2%-20%, where % is the mass percentage.

4. The method for preparing terahertz-controlled conductive aerogel according to claim 1, characterized in that: In the mixed precursor dispersion, the concentration of sodium alginate is 1%-4%, where % is mass percentage.

5. The method for preparing terahertz-controlled conductive aerogel according to claim 1, characterized in that: The conductive filler is MXene, silver nanowire or carbon nanotube.

6. The method for preparing terahertz-controlled conductive aerogel according to claim 1, characterized in that: The time for two-way freezing is 20-60 minutes.

7. The method for preparing terahertz-controlled conductive aerogel according to claim 1, characterized in that: The freeze-drying temperature is -80 to -60°C, and the freeze-drying time is 40 to 50 hours.

8. A terahertz-controlled conductive aerogel, characterized in that: Prepared by the preparation method described in any one of claims 1 to 7.

9. Use of the conductive aerogel according to claim 8 in preparing a terahertz antenna, a terahertz modulator, a terahertz imaging system, a terahertz filter or a terahertz waveguide.

10. The method for regulating terahertz using the conductive aerogel according to claim 8, characterized in that: The method comprises the following steps: compressing the prepared conductive aerogel to change its conductivity, and intelligently regulating the terahertz absorption and birefringence performance of the conductive aerogel according to the change of the conductivity.

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