Preparation and application of an ion gel with underwater adhesion and self-repairing properties

Abstract

The present invention discloses a method for preparing an underwater adhesive self-repairing ion gel. The method mixes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, ionic liquid monomer [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, acrylamide, nano-silica and photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone at room temperature, injects into a polytetrafluoroethylene mold, and initiates polymerization by ultraviolet light to prepare an ion gel. The abundant hydrogen bonds, ion-ion and ion-dipole interactions in the gel network give it high conductivity, excellent mechanical properties, high adhesion and rapid self-healing ability, and it can still be effectively maintained in an underwater environment. The underwater sensor assembled based on this ion gel can maintain stable sensing performance under different strains in an aqueous environment, is suitable for monitoring human motion, etc., and shows good application prospects in the field of underwater sensing and communication.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion gel materials and relates to a preparation method and application of an ion gel with underwater adhesion and self-repairing properties. Background Art

[0002] Wearable devices are inevitably exposed to water during daily activities, such as sweating and underwater exercise. Consequently, the demand for underwater sensing technology is growing. Ion gels, composed of ionic liquids and a supporting network, possess many remarkable properties, including high conductivity, chemical stability, and biocompatibility, making them considered one of the most promising wearable sensors. However, many polymer matrices and ionic liquids are hygroscopic, and the prepared ion gels absorb water molecules from the environment. Under high humidity, the ion gels absorb moisture and swell, resulting in decreased adhesion and conductivity. This makes it difficult for ion gel sensors to maintain long-term stability under high humidity conditions, causing unstable or interrupted output signals and performance degradation of ion gel-based devices, significantly limiting their practical applications. Therefore, improving the underwater stability of ion gels and developing ion gels that exhibit strong adhesion, good mechanical properties, and self-healing properties in aqueous environments are of great significance for the development of underwater wearable sensors.

[0003] The development of ion gels suitable for underwater environments has become an important research area. The construction of a hydrophobic gel network can inhibit the interfacial diffusion of water molecules and other substances, thereby improving the structural and functional stability of ion gels in underwater environments and opening up potential for their underwater applications. For example, Zhu et al. developed a completely hydrophobic ion gel by polymerizing hydrophobic acrylate monomers in the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The hydrophobic polymer network acts as a diffusion barrier between the ion gel region and the aqueous medium, thereby significantly inhibiting the interfacial diffusion of ions and water molecules. Furthermore, the inherent hydrophobicity of the ionic liquid effectively inhibits the diffusion of ions from the ion gel into the aqueous phase. These properties give the ion gel excellent anti-swelling properties and stable electrical and sensing properties underwater (Wang H, Mao Y, Ji D, et al. Transparent, self-adhesive,highly environmentally stable, and water-resistant ionogel enabled reliable strain / temperature sensors and underwater communicators [J]. Chemical Engineering Journal, 2023, 471: 144674). The introduction of abundant CF bonds into the polymer network can eliminate the interference of water molecules, and the corresponding significant hydrophobicity can give the ion gel underwater adhesion. Therefore, the development of new ion gels that combine excellent conductivity, mechanical properties and underwater stability will be effectively used in detecting underwater motion and underwater communications. At present, the preparation of ion gels with multifunctionality and underwater applications still faces challenges.

[0004] The present invention selects [2-(acryloyloxy)ethyl]trimethylammoniumbis(trifluoromethanesulfonyl)imide and acrylamide as comonomers, adds nano-silica and 1-ethyl-3-methylimidazolebis(trifluoromethanesulfonyl)imide, and photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, and prepares ion gel (PIG-407) by photoinitiated polymerization. The prepared ion gel has high conductivity, excellent mechanical properties, high adhesion and rapid self-healing ability. Moreover, the ion gel also maintains good adhesion and self-healing properties in an aqueous environment. Based on these excellent properties of the ion gel, the prepared ion gel has potential applications in underwater human motion monitoring and underwater biological perception. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing an ion gel with underwater adhesion and self-repairing properties, which is used in underwater sensing and communication.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing an ion gel with underwater adhesion and self-healing properties comprises the following steps: adding 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]) to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide [AETA][TFSI], then adding acrylamide (Am), nano-silica (SiO2) and a photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (I2959), dissolving the mixture by ultrasonication and transferring the mixture to a polytetrafluoroethylene mold, and initiating polymerization by ultraviolet light to obtain the ion gel.

[0008] The mass ratio of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:1 to 1:3. The mass ratio of acrylamide to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:3 to 1:16. The mass ratio of nanosilica to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:150 to 1:400. The mass ratio of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:300 to 1:1000. The UV-light-initiated polymerization reaction time is ≥ 30 seconds. The wavelength of the UV light is 365 nm.

[0009] The ion gel prepared by this invention exhibits high conductivity, excellent mechanical properties, strong adhesion, and rapid self-healing capabilities, even exhibiting good adhesion and self-healing abilities underwater. When assembled into a sensor, the prepared ion gel maintains stable sensing performance under varying strains in an aqueous environment, enabling its use as a flexible sensor for monitoring human motion in aquatic environments.

[0010] In summary, the present invention designs and synthesizes a physically cross-linked ion gel. In the gel network, there are hydrogen bonding interactions, ion-ion interactions, and ion-dipole interactions between [AETA][TFSI], [EMIM][TFSI], and Am. −The C-F bonds in [EMIM][TFSI] form dipole-dipole interactions. The NH2 in Am forms hydrogen bonds with the imidazolium cations in [EMIM][TFSI] and the quaternary ammonium cations in [AETA][TFSI]. SiO2, as a nanofiller, is evenly distributed in the ion gel. The reversible hydrogen bond interactions effectively improve the mechanical properties of the ion gel. The high compatibility between the polymer network and [EMIM][TFSI] effectively inhibits the diffusion of ions. The prepared PIG-407 has high transparency and mechanical properties, and maintains good stability and conductivity, as well as adhesion and self-healing properties in an aqueous environment. The ion gel prepared by the present invention has good application prospects in underwater sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the infrared spectrum of the ion gel prepared in Example 1 of the present invention.

[0012] Figure 2 This is an electron microscope image of the microscopic morphology of the ion gel prepared in Example 1 of the present invention.

[0013] Figure 3 This is the energy dispersive X-ray (EDX) mapping image of the ion gel prepared in Example 1 of the present invention.

[0014] Figure 4 Schematic diagram of the conductive properties of the ion gel prepared in the present invention.

[0015] Figure 5 Schematic diagram of the mechanical properties of the ion gel prepared in the present invention.

[0016] Figure 6 Schematic diagram of the underwater adhesion performance of the ion gel prepared in Example 1 of the present invention.

[0017] Figure 7 Schematic diagram of the underwater self-repairing performance of the ion gel prepared in Example 1 of the present invention.

[0018] Figure 8 Schematic diagram of the underwater sensing performance of the ion gel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0020] Example 1

[0021] 0.6 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]) was added to 0.8 g of [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide ([AETA][TFSI]), and then 0.105 g of acrylamide (Am), 0.0041 g of nanosilica (SiO2), and 0.0015 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) were added. After ultrasonic dissolution, the mixture was poured into a polytetrafluoroethylene mold and the polymerization reaction was initiated under 365 nm ultraviolet light for 30 seconds to obtain ion gel (PIG-407).

[0022] Example 2

[0023] 0.4 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was weighed and added to 0.8 g of [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, followed by 0.105 g of acrylamide, 0.0041 g of nanosilica, and 0.0015 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone. After ultrasonic dissolution, the mixture was poured into a polytetrafluoroethylene mold and ultraviolet light was used to initiate the polymerization reaction for 30 seconds to obtain the ion gel PIG-307.

[0024] Example 3

[0025] 0.5 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was weighed and added to 0.8 g of [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, followed by 0.105 g of acrylamide, 0.0041 g of nanosilica, and 0.0015 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone. After ultrasonic dissolution, the mixture was poured into a polytetrafluoroethylene mold and polymerized under 365 nm ultraviolet light for 30 s to obtain ion gel PIG-357.

[0026] Example 4

[0027] 0.75 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was weighed and added to 0.8 g of [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, followed by 0.105 g of acrylamide, 0.0041 g of nanosilica, and 0.0015 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone. After ultrasonic dissolution, the mixture was poured into a polytetrafluoroethylene mold and polymerized under 365 nm ultraviolet light for 30 s to obtain ion gel PIG-457.

[0028] Example 5

[0029] 0.6 g of 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide was weighed and added to 0.54 g, 0.66 g, 0.8 g, and 0.98 g of [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, respectively. Then, 0.105 g of acrylamide, 0.0041 g of nanosilica, and 0.0015 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone were added. After ultrasonic dissolution, the mixture was poured into a polytetrafluoroethylene mold. The polymerization reaction was initiated under 365 nm ultraviolet light for 30 s to obtain ion gels with [AETA][TFSI] contents of 43 wt%, 48 wt%, 53 wt%, and 58 wt%, respectively.

[0030] Example 6

[0031] 0.6 g of 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide was weighed and added to 0.8 g of [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, followed by 0.105 g of acrylamide, 0.0026 g, 0.0041 g, 0.0056 g, and 0.0071 g of nanosilica, and 0.0015 g of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone. After ultrasonic dissolution, the mixture was poured into a polytetrafluoroethylene mold, and the polymerization reaction was initiated under 365 nm ultraviolet light for 30 s to obtain ion gels with nanosilica contents of 0.17 wt%, 0.27 wt%, 0.37 wt%, and 0.47 wt%, respectively.

[0032] Figure 1 This is the infrared spectrum of the PIG-407 ion gel prepared in Example 1, as shown in FIG. Figure 1 The FTIR spectra of PIG-407, [AETA][TFSI], [EMIM][TFSI], and Am are shown. Am is at 3459 cm -1 The characteristic absorption peak of NH2 is shown. The stretching vibration peak in PIG-407 shifts to shorter wave numbers, indicating the presence of a large number of NH2 bonds in the ion gel. The CF3 in [AETA][TFSI] is at 1190 cm -1 The asymmetric bending at 1057 cm -1 The peak at 1354 cm -1 The antisymmetric contraction of SO2 shifts to higher wavenumbers. These results indicate that ion-dipole interactions occur within the [AETA][TFSI] and [EMIM]TFSI molecules. Due to the electronegativity of CF3, ion-ion interactions form between the cation of [EMIM][TFSI] and the anion of [AETA][TFSI].

[0033] The electron microscope image of the microstructure of the ion gel prepared in Example 1. Figure 2 The ion gel has no pores on its surface, and its surface morphology shows that it has the characteristics of a high-density network, further demonstrating the good compatibility between ionic liquids and polymer networks.

[0034] The EDX mapping image of the ion gel prepared in Example 1 is as follows: Figure 3 As shown, the elements N, O, F, S and Si are uniformly distributed in the gel material, which provides the basis for the optical transparency and good adhesion of the ion gel.

[0035] Figure 4 To test the conductivity of the prepared ion gel, the conductivity of different [EMIM][TFSI] and [AETA][TFSI] contents were tested. Figure 4 As shown in Figure 1-a, as the [EMIM][TFSI] content increases, the impedance of the ion gel decreases and the conductivity increases. This is because the higher the [EMIM][TFSI] content, the more ions can move freely in the polymer network, thus increasing the conductivity.

[0036] Then, the effect of [AETA][TFSI] on the conductivity of ion gel was investigated. The content of [EMIM][TFSI] was controlled at 40 wt%. As the content of [AETA][TFSI] increased, the impedance of ion gel increased and the conductivity decreased ( Figure 4 -b). This is because after polymerization, the migration of polycations is restricted, reducing ion mobility. Considering the electrochemical and mechanical properties of the gel sample, the [EMIM][TFSI] content was selected to be 40 wt% and the [AETA][TFSI] content to be 43 wt%.

[0037] Figure 5 The mechanical properties test results of the prepared ion gel were investigated to explore the effects of different [EMIM][TFSI] and SiO2 mass ratios on the mechanical properties. Figure 5 -a shows that with the increase of [EMIM][TFSI] content, the stress and strain of the ion gel are also greatly affected. This is because the addition of [EMIM][TFSI] can improve its elongation and make it have good compatibility, thereby further affecting the mechanical properties.

[0038] When the mass of Am and [EMIM][TFSI] is kept constant, the tensile properties of the ion gel are affected by the addition of SiO2. Its elongation at break increases from 700% to 1600%, and its fracture strength increases from 15 kPa to 70 kPa ( Figure 5 -b), greatly improving the mechanical properties, which is due to the reversible hydrophobic interaction between the gel network and SiO2 nanoparticles that can effectively dissipate energy.

[0039] Figure 6 The underwater adhesion test results of the ion gel prepared in Example 1 were obtained by immersing the sample in H2O, NaOH, NaCl, and HCl solutions for 1 hour to test its adhesion strength. It can be seen that the adhesion strength of PIG-407 after immersion in H2O, NaOH, NaCl, and HCl solutions reached 246 kPa, 380 kPa, 180 kPa, and 298 kPa, respectively. This is because the fluorine-containing PIG-407 sample can eliminate the interference of water molecules, destroy the hydration layer on the substrate surface, and enhance adhesion in water.

[0040] Figure 7 Schematic diagram of the underwater self-healing of the ion gel prepared in Example 1. Two pieces of PIG-407 dyed with methylene blue and methyl orange were placed in contact. It can be seen that the two pieces of PIG-407 with different colors healed together and could be stretched, both in the environment and in the aquatic environment.

[0041] Figure 8 This is a schematic diagram of the sensing performance of the ion gel prepared in Example 1. The assembled PIG-407 sensor is fixed on the finger joint and completely immersed in a container filled with water. The signal output by the PIG-407 sensor is not affected by water and shows good underwater stability ( Figure 8 -a). The ion gel sensor can be fixed on the body of an aquatic animal. For example, select an electric toy fish model and attach PIG-407 to the left side of the fish's tail. As the fish sways left and right while swimming, the sensor can continuously capture the electrical signal of the tail's movement. The fish's turning direction and speed can be determined based on the strength and duration of the signal. Figure 8 -b). This indicates that the gel has good sensitivity and stability to the water environment and has great application potential in the field of underwater biological monitoring.

Claims

1. A method for preparing an ion gel with underwater adhesion and self-repairing properties, characterized by: 1-Ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide was added to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide, and then acrylamide, nano-silica and photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone were added. After ultrasonic dissolution, the mixture was transferred to a polytetrafluoroethylene mold and polymerized by ultraviolet light to obtain an ion gel.

2. The method for preparing an ion gel according to claim 1, wherein: The mass ratio of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:1~1:

3.

3. The method for preparing an ion gel according to claim 1, wherein: The mass ratio of acrylamide to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:3-1:

16.

4. The method for preparing an ion gel according to claim 1, wherein: The mass ratio of nano-silica to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:150-1:

400.

5. The method for preparing an ion gel according to claim 1, wherein: The mass ratio of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone to [2-(acryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide is 1:300 to 1:1000.

6. The method for preparing an ion gel according to claim 1, wherein: The UV-induced polymerization reaction time is ≥30s.

7. The method for preparing an ion gel according to claim 1, wherein: The wavelength of ultraviolet light is 365nm.

8. Use of the ion gel prepared by the method according to claim 1 in underwater sensing.

9. The use according to claim 8, characterized in that: The ion gel is used as a flexible sensor to monitor human motion in real time in an aqueous environment for the purpose of non-disease diagnosis and treatment.

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