Preparation method of polyvinyl alcohol-based electromagnetic shielding conductive hydrogel

Abstract

The invention discloses a preparation method of polyvinyl alcohol-based electromagnetic shielding conductive hydrogel. The preparation method comprises the following steps: (1) preparing a high-concentration dimethyl sulfoxide aqueous solution; adding polyvinyl alcohol into the dimethyl sulfoxide aqueous solution, heating and stirring to completely dissolve the polyvinyl alcohol to obtain a mixed solution; (2) putting the mixed solution after standing into a mold, and freezing at low temperature to obtain PVA gel; (3) an electrolyte salt solution is prepared, and the electrolyte salt solution contains low-concentration dimethyl sulfoxide; and placing the PVA gel in an electrolyte salt solution, and carrying out ion exchange to obtain the polyvinyl alcohol-based electromagnetic shielding conductive hydrogel. The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared by the method has high transparency, strength and ionic conductivity, the light transmittance reaches up to 75.2%, and the compressive strength reaches up to 2.97 MPa when the strain is 80%; the ionic conductivity can reach 10.34 mS / cm; meanwhile, the effective electromagnetic shielding effectiveness (gt; gt) can still be kept at the low temperature of-60 DEG C for more than 60 hours; 30 dB).

Description

Technical Field

[0001] The invention relates to a method for preparing a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel. Background Art

[0002] With the advent of the 5G information age, various portable communication devices are increasingly used in life. Electronic components and complex circuits controlled by wireless networks will inevitably generate a large amount of electromagnetic radiation and electromagnetic interference, which seriously affects the normal operation of sensitive electronic equipment systems and human health. Considering the rapid development of deformable and wearable electronic devices, there is an urgent need for efficient electromagnetic interference shielding materials with high transparency, good mechanical properties and low temperature stability.

[0003] Hydrogels have excellent conductivity, flexibility, compression resistance and biocompatibility. They have unique advantages and potential in the development of deformable and wearable electromagnetic shielding materials, and have gradually become an important research target in academia and industry. For example, the team of Associate Professor Liu Xiaofang and Professor Yu Ronghai from Beihang University prepared a MXene organic hydrogel with MXene as a conductive network and water / glycerol binary solvent as an ion transmission channel. It has excellent electromagnetic shielding function. When the MXene content is 1.1wt%, the highest electromagnetic shielding efficiency of MXene hydrogel is 33.6dB (Yu, YH; Yi, P.; Xu, WB; Sun, X.; Deng, G.; Liu, XF; Shui, JL; Yu, RHEnvironmentally tough and stretchable MXene organohydrogel with exceptionally enhanced electromagnetic interference shielding performances, Nano-Micro Lett. 14 (2022) 77). He et al. from Southeast University studied and prepared aero / organo / hydrogels with gravity-induced asymmetric gradient structure, and its total electromagnetic shielding effectiveness reached 86.9 dB (He, M.; Lv, XL; Li, ZH; Li, HY; Qian, W.; Zhu, SY; Zhou, YM; Wang, YJ; Bu, XH Research on efficient electromagnetic shielding performance and modulation mechanism of aero / organo / hydrogels with gravity-induced asymmetric gradient structure, Small 20 (2024) 2403210). Although the above hydrogel materials are quite effective in electromagnetic shielding, with the development of flexible electronics, communication technology and polar exploration technology, hydrogel materials, as the core protective materials of high-end equipment, need to be applied to multifunctional scenarios that take into account environmental adaptability (low temperature) and intelligent interaction (transparent visualization). For the above hydrogel materials, they are very easy to crack at low temperature, and it is difficult to maintain transparency to achieve the function of maintaining screen display. At the same time, it is difficult to maintain electromagnetic shielding performance in an environment below -5°C. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for preparing a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel. The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared by this method has high transparency, strength and ionic conductivity, and still has good electromagnetic shielding performance at extremely low temperatures (-60°C).

[0005] Technical solution: The method for preparing the polyvinyl alcohol-based electromagnetic shielding conductive hydrogel of the present invention comprises the following steps:

[0006] (1) preparing a high concentration of dimethyl sulfoxide (DMSO) aqueous solution; adding polyvinyl alcohol (PVA) to the dimethyl sulfoxide aqueous solution, heating and stirring to completely dissolve the PVA to obtain a mixed solution; and allowing the obtained mixed solution to stand for a period of time to remove bubbles in the solution;

[0007] (2) placing the mixed solution after standing still in a mold and freezing it at low temperature to obtain PVA gel;

[0008] (3) preparing an electrolyte salt solution containing DMSO, wherein the electrolyte salt solution contains a low concentration of dimethyl sulfoxide; placing the PVA gel in the electrolyte salt solution, and obtaining a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel after ion exchange.

[0009] Wherein, in step (1), the volume fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 55-60%

[0010] Wherein, in step (1), the added mass volume ratio of polyvinyl alcohol to dimethyl sulfoxide is 1.5g:9-12mL.

[0011] Wherein, in step (1), the heating temperature is 90-95° C., the heating stirring time is 50-60 min; and the standing time is 10-15 min.

[0012] Wherein, in step (2), the freezing temperature is -20 to -25°C; and the freezing time is 10 to 12 hours.

[0013] Wherein, in step (3), in the electrolyte salt solution, the electrolyte salt is one of NaCl, KCl or MgCl2; and the mass concentration of the electrolyte salt is 3.15 to 3.2 mg / mL.

[0014] Wherein, in step (3), the volume fraction of dimethyl sulfoxide in the electrolyte salt solution is 30 to 35%.

[0015] Wherein, in step (3), the ion exchange time is 12 to 14 hours.

[0016] The formation of hydrogen bonds in the electromagnetic shielding conductive hydrogel prepared by the present invention (hydrogen bonds are formed based on the interaction between hydrogen atoms in the polyvinyl alcohol molecular chain and oxygen atoms in the dimethyl sulfoxide molecule) can help regulate the interaction between PVA molecules, reduce light scattering, and thus increase the transparency of the hydrogel. The formation of hydrogen bonds also helps the hydrogel to have good mechanical properties. The PVA-based hydrogel itself has a certain ion conductivity. By adding an electrolyte salt solution, cations and anions in the solution can move freely in the hydrogel, thereby forming a conductive path in the hydrogel, significantly enhancing its ionic conductivity, and helping to achieve the electromagnetic shielding function. At the same time, this method not only improves the conductivity of the hydrogel, but also keeps it in good mechanical properties (the preparation method of the present invention can achieve a dual improvement in the conductivity and mechanical properties of the hydrogel. On the one hand, by introducing an electrolyte salt solution, cations and anions can move freely in the hydrogel to form a conductive path, thereby significantly enhancing its ionic conductivity; this improvement in conductivity provides a possibility for the application of hydrogel in the field of electromagnetic shielding; on the other hand, the present invention promotes the hydroxyl groups in the polyvinyl alcohol molecular chain to move freely in the hydrogel to form a conductive path, thereby significantly enhancing its ionic conductivity; this improvement in conductivity provides a possibility for the application of hydrogel in the field of electromagnetic shielding; on the other hand, the present invention promotes the The hydrogen bonds formed between DMSO and oxygen atoms in dimethyl sulfoxide molecules effectively regulate the interaction between PVA molecules; the formation of such hydrogen bonds not only reduces light scattering and improves the transparency of the hydrogel, but also enhances the network structure inside the hydrogel, giving it good mechanical properties, so that while enhancing the conductivity, the hydrogel can still maintain its structural stability and toughness, and is not prone to rupture or deformation); adding DMSO in the process of forming PVA-based hydrogel can effectively improve the antifreeze performance of the hydrogel, because DMSO can form hydrogen bonds with water molecules (this hydrogen bond is a hydrogen bond formed between dimethyl sulfoxide (DMSO) and water molecules, and the formation of such hydrogen bonds is crucial to improving the antifreeze performance of the hydrogel; DMSO molecules can be tightly bound to water molecules through hydrogen bonds, thereby reducing the degree of freedom of water molecules in the hydrogel and reducing the formation of ice crystals. This effect enables the hydrogel to maintain good flexibility and elasticity at low temperatures, avoiding structural damage and performance degradation caused by freezing), and this hydrogen bonding effect can lower the freezing point and volatility point of water, so that the PVA-based hydrogel can still maintain its good electromagnetic shielding performance at low temperatures.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared by the method of the present invention has high transparency, strength and ionic conductivity, a light transmittance of up to 75.2%, a compressive strength of up to 2.97 MPa at a strain of 80%, and an ionic conductivity of up to 10.34 mS / cm; at the same time, it can still maintain effective electromagnetic shielding performance (>30 dB) at a low temperature of -60°C for more than 60 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a digital photo of the conductive hydrogel S prepared in Example 1;

[0019] Figure 2 is the FTIR curve of the conductive hydrogel S prepared in Example 1;

[0020] Figure 3 is the transmittance of the conductive hydrogel S prepared in Example 1 within the visible light wavelength range;

[0021] Figure 4 is a compressive stress-strain curve of the conductive hydrogel S prepared in Example 1;

[0022] Figure 5 The electromagnetic shielding effectiveness diagram of the conductive hydrogel S prepared in Example 1 and its S-LD30 after being frozen for 30 hours and S-LD60 after being frozen for 60 hours. DETAILED DESCRIPTION

[0023] Example 1

[0024] The method for preparing the polyvinyl alcohol-based electromagnetic shielding conductive hydrogel of the present invention comprises the following steps:

[0025] (1) 12 mL of DMSO and 8 mL of deionized water were mixed and stirred at 700 r / min for 10 min to obtain a DMSO aqueous solution;

[0026] (2) adding 1.5 g of PVA to the DMSO aqueous solution of step (1), heating and stirring at 90° C. for 50 min, and then standing for 10 min to obtain a mixed solution in which the PVA is completely dissolved and free of excess bubbles;

[0027] (3) placing the mixed solution of step (2) in a customized (shaped) polytetrafluoroethylene mold, and then placing the polytetrafluoroethylene mold containing the mixed solution in a freezer layer of a refrigerator and freezing it for 10 hours to gel; obtaining a gel product;

[0028] (4) 2.8 g NaCl and 50 mL deionized water were mixed and stirred for 10 min to obtain solution A; then 30 mL DMSO and 8 mL deionized water were mixed and stirred for 10 min to obtain solution B; then solution A and solution B were mixed and stirred for 10 min to obtain an electrolyte salt solution;

[0029] (5) placing the gel product of step (3) in the electrolyte salt solution of step (4) for 12 hours, and after reaching ion exchange equilibrium, obtaining a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel, denoted as S.

[0030] Figure 1 This is a digital photo of the conductive hydrogel S prepared in Example 1. Figure 1It can be seen that the product S obtained by gel treatment and ion exchange method has a complete hydrogel structure, indicating that the PVA is completely dissolved, and the appearance of the product can be customized by a customized mold. It can be observed that the blue gloves can be seen through the product S, indicating that the S product has a certain transparency. In addition, the product S has almost no deformation when squeezed by hand, indicating that the product S exhibits good mechanical compression resistance.

[0031] Figure 2 is the FTIR curve of the conductive hydrogel S prepared in Example 1. Figure 2 It can be seen that the wave number observed in the infrared wave number range is 3264cm -1 3306cm -1 The absorption peaks at the locations are the -OH stretching vibration peak between the hydrogen atoms in the polyvinyl alcohol molecular chain and the oxygen atoms in the dimethyl sulfoxide molecule and the -OH stretching vibration peak formed between dimethyl sulfoxide and water molecules, respectively, proving that there are two types of hydrogen bonds in the prepared material.

[0032] Figure 3 The transmittance diagram of the product S obtained in Example 1 in the visible light wavelength range is shown in FIG. Figure 3 It can be seen that within the visible light wavelength range, i.e., from 400 nm to 780 nm, the transmittance of the product S increases with increasing wavelength, and a maximum transmittance of 75.2% is obtained at 780 nm, proving that the prepared material is an optically transparent hydrogel material.

[0033] Figure 4 is the compressive stress-strain curve of the product S obtained in Example 1, from Figure 4 It can be seen that the compressive strength of the product S prepared in Example 1 is as high as 2.97 MPa when the compressive strain is 80%, indicating that the formation of hydrogen bonds and subsequent ion exchange in the polyvinyl alcohol-based electromagnetic shielding conductive hydrogel of the present invention enables it to maintain good mechanical properties and is more suitable for harsh environments.

[0034] After freezing it (at -60°C) for 60 hours, its optical transmittance at 780 nm was 73.5%, and its compressive strength at a strain of 80% was 2.84 MPa.

[0035] The product S obtained in Example 1 was frozen at (-60°C) for 30 hours and 60 hours and was recorded as S-LD30 and S-LD60 respectively.

[0036] Figure 5 The electromagnetic shielding effectiveness diagram of product S and its S-LD30 after 30h freezing and S-LD60 after 60h freezing. Figure 5It can be seen that within the frequency range of 8.2 GHz to 12.4 GHz, the samples showed good electromagnetic shielding performance both before and after freezing at -60°C. When the hydrogel thickness was 2 mm, the average electromagnetic shielding effectiveness of S, S-LD30 and S-LD60 were 41.21 dB, 38.19 dB and 34.28 dB, respectively, and the conductivity values ​​of the three were 10.34 mS / cm, 8.62 mS / cm and 6.89 mS / cm, respectively. It can be seen that the conductive hydrogel prepared by the present invention can withstand a low temperature of -60°C for more than 60 hours and still maintain effective electromagnetic shielding effectiveness (>30 dB). The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared by the present invention achieves high transmittance, excellent compression resistance, strong antifreeze properties, high conductivity and effective electromagnetic shielding effectiveness under low temperature conditions.

[0037] Example 2

[0038] The method for preparing the polyvinyl alcohol-based electromagnetic shielding conductive hydrogel of the present invention comprises the following steps:

[0039] (1) 9.8 mL of DMSO and 8 mL of deionized water were mixed and stirred at 700 r / min for 10 min to obtain a DMSO aqueous solution;

[0040] (2) adding 1.5 g of PVA to the DMSO aqueous solution of step (1), heating and stirring at 95° C. for 60 min, and then standing for 15 min to obtain a mixed solution in which the PVA is completely dissolved and free of excess bubbles;

[0041] (3) placing the mixed solution of step (2) in a customized polytetrafluoroethylene mold, and then placing the polytetrafluoroethylene mold containing the mixed solution in a freezer layer of a refrigerator for 12 hours to gel; obtaining a gel product;

[0042] (4) 2.8 g KCl and 50 mL deionized water were mixed and stirred for 10 min to obtain solution A; then 30 mL DMSO and 8 mL deionized water were mixed and stirred for 10 min to obtain solution B; then solution A and solution B were mixed and stirred for 10 min to obtain an electrolyte salt solution;

[0043] (5) The gel product of step (3) is placed in the electrolyte salt solution of step (4) for 14 hours. After reaching ion exchange equilibrium, a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel is obtained, which is recorded as S1.

[0044] The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared in Example 2 has a light transmittance of 68.4% at 780nm, a compressive strength of 2.86MPa at a strain of 80%, an ionic conductivity of 6.53mS / cm, and an average electromagnetic shielding effectiveness of 32.53dB at a low temperature of -60°C for 60h.

[0045] Comparative Example 1

[0046] Same as Example 1, except that the content of NaCl is 2.0 g.

[0047] The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared in Comparative Example 1 has a light transmittance of 74.7% at 780nm, a compressive strength of 2.89MPa at a strain of 80%, an ionic conductivity of 5.90mS / cm, and an average electromagnetic shielding effectiveness of 29.35dB at a low temperature of -60°C for 60h.

[0048] Comparative Example 2

[0049] Same as Example 1, except that the ion exchange time is 6 hours.

[0050] The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared in Comparative Example 2 has a light transmittance of 66.8% at 780nm, a compressive strength of 2.91MPa at a strain of 80%, an ionic conductivity of 6.17mS / cm, and an average electromagnetic shielding effectiveness of 30.19dB at a low temperature of -60°C for 60h.

[0051] Comparative Example 3

[0052] Same as Example 1, except that DMSO is not added in step (4).

[0053] The polyvinyl alcohol-based electromagnetic shielding conductive hydrogel prepared in Comparative Example 3 has a light transmittance of 52.7% at 780nm, a compressive strength of 2.35MPa at a strain of 80%, an ionic conductivity of 5.54mS / cm, and an average electromagnetic shielding effectiveness of 28.74dB at a low temperature of -60°C for 60h.

Claims

1. A method for preparing a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel, characterized in that: The steps include: (1) preparing a high concentration of dimethyl sulfoxide aqueous solution; adding polyvinyl alcohol to the dimethyl sulfoxide aqueous solution, heating and stirring to completely dissolve the polyvinyl alcohol, and obtaining a mixed solution; (2) placing the mixed solution after standing still in a mold and freezing it at low temperature to obtain PVA gel; (3) preparing an electrolyte salt solution, wherein the electrolyte salt solution contains a low concentration of dimethyl sulfoxide; placing the PVA gel in the electrolyte salt solution, and obtaining a polyvinyl alcohol-based electromagnetic shielding conductive hydrogel after ion exchange.

2. The preparation method according to claim 1, characterized in that: In step (1), the volume fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 55-60%.

3. The preparation method according to claim 1, characterized in that: In step (1), the added mass volume ratio of polyvinyl alcohol to dimethyl sulfoxide is 1.5g:9-12mL.

4. The preparation method according to claim 1, characterized in that: In step (1), the heating temperature is 90-95° C., and the heating stirring time is 50-60 min.

5. The preparation method according to claim 1, characterized in that: In step (2), the mixed solution is allowed to stand for 10 to 15 minutes.

6. The preparation method according to claim 1, characterized in that: In step (2), the freezing temperature is -20 to -25°C and the freezing time is 10 to 12 hours.

7. The preparation method according to claim 1, characterized in that: In step (3), in the electrolyte salt solution, the electrolyte salt is one of NaCl, KCl or MgCl2; and the concentration of the electrolyte salt is 3.15 to 3.2 mg / mL.

8. The preparation method according to claim 1, characterized in that: In step (3), the volume fraction of dimethyl sulfoxide in the electrolyte salt solution is 30 to 35%.

9. The preparation method according to claim 1, characterized in that: In step (3), the ion exchange time is 12 to 14 hours.

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