阅读说明：本技术 一种利用空间调整策略提高光固化离子凝胶电导率和灵敏度的方法 (Method for improving conductivity and sensitivity of photocuring ionic gel by using spatial adjustment strategy ) 是由 何勇 张超 姚淼 聂俊 于 2021-10-18 设计创作，主要内容包括：离子凝胶的高电导率和作为传感器的高灵敏度一直是巨大的挑战。本发明提出了一种空间调整策略,在不改变离子凝胶内化合物类型和比例的情况下,通过减少空间阻碍来提高电导率和灵敏度。在离子凝胶制备过程中添加可去除的空间预占位剂减少了聚合物链的缠结,从而改善聚合物网络的流动性。凝胶成型后除去空间预占位剂,获得的自由体积可以促进离子的移动和聚合物的迁移。通过这种方式,成功地提高了离子凝胶的电导率和灵敏度,同时保持了其良好的透明性、拉伸性、稳定性和机电性能,如快速的响应速度和良好的重复性。这种简单有效的策略对化学结构没有特殊要求,因此在各种系统中具有广泛的适用性,为柔性传感器的发展开辟了一条新的途径。(The high conductivity of ionic gels and the high sensitivity as sensors have been a great challenge. The invention provides a spatial adjustment strategy, which improves the conductivity and the sensitivity by reducing spatial obstruction under the condition of not changing the type and the proportion of compounds in the ionic gel. The addition of the removable space pre-placeholder during the preparation of the ionic gel reduces entanglement of the polymer chains, thereby improving the mobility of the polymer network. The space pre-placeholder is removed after the gel is formed and the free volume obtained can facilitate the movement of ions and the migration of the polymer. In this way, the conductivity and sensitivity of the ionic gel are successfully improved, and simultaneously, the good transparency, stretchability, stability and electromechanical properties, such as fast response speed and good repeatability, are maintained. The simple and effective strategy has no special requirements on chemical structures, so that the method has wide applicability in various systems, and opens up a new way for the development of flexible sensors.)

1. A method for improving the conductivity and sensitivity of photo-cured ionic gel by using a space adjustment strategy is characterized in that an inert and removable space pre-occupying agent is added during the preparation of the ionic gel, the ionic gel is removed after the preparation of the ionic gel is completed by using a photo-curing technology, and the conductivity and sensitivity of the ionic gel are improved by utilizing the reduction of the entanglement degree of polymer molecular chains caused by adding the pre-occupying agent and the reduction of the space density of the gel caused by removing the pre-occupying agent.

2. The method according to claim 1, wherein the space pre-occupying agent is a volatile small-molecule organic compound, such as one or more of methanol, ethanol, isopropanol, acetone, butanone, diethyl ether, dichloromethane, cyclohexane, and ethyl acetate.

3. The method of claim 1, wherein the gel is a polyacrylate and is prepared by a free radical crosslinking reaction of a monofunctional acrylate monomer and an acrylate crosslinking agent, the monomer being 1-3 of acrylic acid, ethyl acrylate, butyl acrylate, n-octyl acrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, dimethylaminoethyl acrylate, hexafluorobutyl acrylate, and the crosslinking agent being 1-2 of ethylene glycol dimethacrylate, 1, 6-hexanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate.

4. The method according to claim 1, wherein the cation of the ionic liquid is one of imidazoles, pyridines, quaternary amines, quaternary phosphines, pyrrolidines, and piperidines with different alkyl substituents, and the anion is one of chlorine, bromine, iodine, tetrafluoroboric acid, hexafluorophosphoric acid, bistrifluoromethanesulfonylimide, trifluoroacetic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid.

5. The method according to claim 1, wherein the ionic gel is prepared by mixing the ionic liquid, the monomer, the cross-linking agent, the space pre-occupying agent and the photoinitiator uniformly, curing the mixture by ultraviolet light to form a gel, and finally removing the space pre-occupying agent by a vacuum drying method.

Technical Field

The invention relates to the field of sensor materials based on ionic liquid gel, in particular to a general strategy for improving the conductivity and sensitivity of ionic gel, which is mainly applied to the aspect of flexible sensors.

Background

In recent years, flexible/stretchable electronic devices have shown good application prospects in the field of frontalong, such as flexible sensors, electronic skins, human-computer interaction interfaces, flexible batteries, and the like. The flexible sensor refers to an electronic device which can deform in a certain range, has greater flexibility compared with the traditional electronic device, and can adapt to different working environments to a certain extent. Electronic skin is an artificial electronic material with skin function, which simulates human skin to experience external stimuli (pressure, temperature, humidity) by converting mechanical deformation of flexible electronic devices into electrical signals.

The ionic gel is composed of a polymer network swelled by ionic liquid, and has good stretchability and transparency. Meanwhile, the ionic gel retains inherent characteristics of the ionic liquid, such as high ionic conductivity (-1 mS/cm), low volatility, thermal and chemical stability, wide electrochemical window and non-flammability, and shows significant advantages over hydrogel.

High conductivity and high sensitivity ionic gels are a constant goal pursued by researchers. The conductivity is usually increased by selecting ionic liquids with higher conductivity or increasing the content of ionic liquids, which requires high compatibility and high capacity of ionic liquids in the crosslinked polymer network, thus risking leakage of the liquid and difficulties in selecting the type of ionic liquid and polymer. The sensitivity of ionic gels is related to the rearrangement rate of polymer chains and ionic liquids during deformation, and is currently adjusted only by changing the type of polymer and ionic liquid.

In addition to the type and content of ionic liquid, the mobility of ionic liquid and polymer network in the gel is also a key factor in determining conductivity and sensitivity, and can be controlled by steric hindrance of the polymer network. The degree of steric hindrance is determined by the spatial density and the degree of entanglement, with lower spatial density and lower degree of entanglement resulting in higher motion ability. If the steric hindrance of the polymer network can be reduced, thereby improving the mobility of the polymer network and the mobility of the ionic liquid in the ionic gel, an ionic gel having higher conductivity and sensitivity can be obtained.

Disclosure of Invention

The invention aims to provide a universal and simple spatial adjustment strategy for improving the conductivity and sensitivity of ionic gel. In preparing the ionic gel, an inert and removable space pre-placeholder is added to the solution to pre-occupy a certain space. It has been shown that the concentration of monomer during polymerization affects the degree of entanglement of the polymer network. Entanglement occurs more readily when the gel is polymerized from a more concentrated solution. Thus, in the present strategy, the additional solvent to dilute the monomer will reduce polymer entanglement during network formation, thereby making the polymer network more fluid. After the ionic gel is formed, the space released after removal of the space pre-placeholder forms free volumes in the ionic gel, and then the ionic liquid and part of the polymer chain segments will spontaneously move into these free spaces with an average spatial density, thereby obtaining a higher mobility.

The ionic gel is prepared by selecting the ionic liquid and the monomer with better compatibility, and the selected space pre-occupying agent has good compatibility and proper volatility with the ionic liquid and the polymer. A transparent ionic gel free from ionic liquid leakage is prepared by photopolymerization by a one-pot method by selecting a proper cross-linking agent and 1 wt% of 2-hydroxy-2-methyl-1-phenyl-1-acetone (1173) as a photoinitiator. The space pre-placeholder is added during preparation in a volume ratio (space pre-placeholder/solution) and is finally removed after the ionic gel is formed.

With the change of the state of the polymer network, the conductivity of the ionic gel changes (after the space adjustment, the ionic liquid obtains more free volume, which is beneficial to ion migration, and the conductivity of the ionic gel is improved.

Through spatial adjustment, the ionic gel tensile property is obviously improved. The polymer network and the ionic liquid are rearranged simultaneously in the stretching process, so the improvement of the stretching performance of the ionic gel is mainly determined by the reduction of physical entanglement among polymer chains after space adjustment, and the reduction of the physical entanglement among the polymer chains means that the molecular chains have better fluidity, thereby realizing higher elongation at break. After the spatial adjustment, due to the reduction of entanglement among polymer molecular chains and the adjustment of spatial density, the rearrangement speed of the polymer chains and the ionic liquid is accelerated, and compared with gel without the spatial adjustment, the sensor prepared from the ionic gel after the spatial adjustment has higher sensitivity under the condition that chemical components and proportion are not changed.

Detailed Description

Example 1

1) Butyl acrylate and 1-butyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt in a molar ratio of 1:0.46 were mixed homogeneously.

2) 1173 (1 wt% relative to monomer) and 1, 6-hexanediol diacrylate (0.6 mol% relative to monomer) were dissolved in the solution.

3) 5/8 volume ratio (ethanol/solution) of ethanol was added as a space pre-spacer to the solution and the solution was sonicated for 5 minutes.

4) Transferring the solution toIn a mold made of a pair of glass plates sandwiching a silica gel spacer, and then using a mold having a strength of 80 mW/cm²And ultraviolet light with the wavelength of 365 nm irradiates for 300 s.

5) The ionic gel was placed in a vacuum oven at 60 ℃ for 6 hours to remove the ethanol. The properties of the ionic gel are shown in table 1.

Example 2

The monomers and ionic liquid used were ethyl acrylate and 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt (molar ratio 1: 0.5). The cross-linking agent is ethylene glycol dimethacrylate (0.8 mol% relative to the monomer), the space pre-occupying agent is acetone, and the temperature of the vacuum oven is 40 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 3

The monomers and ionic liquid used were hydroxypropyl acrylate and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (molar ratio 1: 0.4). The cross-linking agent was tripropylene glycol diacrylate (0.8 mol% relative to the monomer), the space pre-occupying agent was methanol and the temperature of the vacuum oven was 50 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 4

The monomers and ionic liquids used were exchanged for hexafluorobutyl acrylate and N-ethylpyridine bis (trifluoromethanesulfonyl) imide salt (molar ratio 1: 0.45). The cross-linking agent is dipentaerythritol hexaacrylate (1 mol% relative to the monomer), the space pre-occupying agent is ethyl acetate, and the temperature of the vacuum oven is 65 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 5

The monomers and ionic liquid used were exchanged for acrylic acid and 1-ethyl-3-methylimidazolium chloride (molar ratio 1: 0.38). The crosslinker was trimethylolpropane triacrylate (0.6 mol% relative to monomer), the space pre-spacer was diethyl ether and the temperature of the vacuum oven was 30 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 6

The monomers and ionic liquids used were replaced by dimethylaminoethyl acrylate, butyl acrylate and tributylmethylammonium bis (trifluoromethanesulfonyl) imide salt (molar ratio 1:1: 0.8). The crosslinker was pentaerythritol tetraacrylate (0.8 mol% relative to the monomer), the space pre-occupying agent was dichloromethane, and the temperature of the vacuum oven was 35 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 7

The monomers and ionic liquids used were replaced with hydroxyethyl acrylate, hydroxypropyl acrylate and 1-ethyl-3-methylimidazolium tetrafluoroborate (molar ratio 1:0.9: 0.9). The crosslinker was pentaerythritol triacrylate (1 mol% relative to the monomers), the space pre-occupying agent was isopropanol, and the temperature of the vacuum oven was 60 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 8

The monomers and ionic liquids used were changed to n-octyl acrylate, acrylic acid and 1-octyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt (molar ratio 1:0.5: 0.85). The cross-linking agent is dipentaerythritol hexaacrylate (0.8 mol% relative to the monomer), the space pre-occupying agent is ethanol, and the temperature of the vacuum oven is 60 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 9

The monomers and ionic liquids used were changed to butyl acrylate, acrylic acid, ethyl acrylate and 1-butyl-3-methylimidazolium hexafluorophosphate (molar ratio 1:0.5:0.5: 0.9). The cross-linking agent was tripropylene glycol diacrylate (0.6 mol% relative to the monomer), the space pre-occupying agent was acetone and the temperature of the vacuum oven was 40 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 10

The monomers and ionic liquid are replaced by ethyl acrylate, hydroxyethyl acrylate, dimethylaminoethyl acrylate and 1-ethyl-3-methylimidazolium dinitrile amine salt (molar ratio is 1:0.6:1: 1). The cross-linking agent is ethylene glycol dimethacrylate (1 mol percent relative to the monomer), the space pre-occupying agent is butanone, and the temperature of the vacuum oven is 60 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 11

The monomers and ionic liquid are hydroxypropyl acrylate, hydroxyethyl acrylate, hexafluorobutyl acrylate and 1-propyl-3-methylimidazolium tetrafluoroborate (molar ratio is 1:0.6:0.8: 0.85). The crosslinker was pentaerythritol triacrylate (0.8 mol% relative to monomer), the space pre-placeholder was dichloromethane, and the temperature of the vacuum oven was 35 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

Example 12

The monomers and ionic liquid are replaced by acrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate and 1-ethyl-3-methylimidazole p-methylbenzene sulfonate (molar ratio is 1:1:0.5: 0.9). The cross-linking agent is ethylene glycol dimethacrylate (0.1 mol% relative to the monomer), the space pre-occupying agent is methanol, and the temperature of the vacuum oven is 50 ℃. The other experimental procedures were the same as in example 1. The properties of the ionic gel are shown in table 1.

TABLE 1 comparison of Performance of spatially conditioned Ionic gels with non-spatially conditioned Ionic gels in the examples

Note: the control values are measured with the same monomer, crosslinker, ionic liquid, photoinitiator composition as in the examples, by the same preparation process, but without the addition of a space pre-placeholder system.