Preparation method of thermal response intelligent ionic gel for intelligent temperature sensing

Abstract

The invention provides a preparation method of thermal response intelligent ionic gel for intelligent temperature sensing. A traditional thermoelectric material is an electronic system based on a semiconductor, and the Seebeck coefficient of the traditional thermoelectric material is relatively low (10-102 [mu] V / K). An ionic thermoelectric material can realize thermoelectric power jump (about 10 mV / K) by virtue of a Sore effect, but still has the limitations of single thermoelectric polarity, incapability of dynamic switching and the like, and is difficult to meet the requirements of current intelligent wearable equipment on high sensitivity and intelligence (such as a feedback function) of a thermal sensor. According to the preparation method of the p-n switchable thermoelectric ionic gel based on the low critical intersoluble temperature (LCST) phase change behavior, in-situ reversible switching of thermoelectric polarities is achieved through material intrinsic phase transition, and intelligent temperature feedback is achieved through polarity inversion; through the pi-shaped series connection of the p-n type thermoelectric units, the device structure is simplified, the temperature detection sensitivity is improved, and the device can be applied to intelligent thermal management of electronic equipment, wearable health monitoring and industrial abnormal temperature rise diagnosis.

Description

Technical Field

[0001] The invention belongs to the technical field of ion gel. Background Art

[0002] Thermoelectric materials have shown important application value in energy recovery, wearable electronics, smart sensing and other fields because they can directly convert thermal energy into electrical energy and achieve accurate detection of temperature gradients. Traditional thermoelectric materials are based on the Seebeck effect and rely on the thermal diffusion of electrons or holes to generate thermovoltage, but their Seebeck coefficient is generally low (about 10-10 2 The low electrical conductivity of insulating materials (~10-12 Ω / cm) severely limits detection sensitivity. While insulating materials can exhibit high thermoelectric power (~1 mV / K), their extremely low electrical conductivity (10-12 Ω / cm) makes it difficult to construct practical thermocouples. To increase the output signal, a large number of thermoelectric units must typically be connected in series, resulting in a complex and costly fabrication process, limiting large-scale application.

[0003] In recent years, the rise of ionic thermoelectric materials has provided a new approach to solving the above bottlenecks. Ionic thermoelectric materials are based on the Soret effect, which generates thermovoltage through the thermal diffusion of ions under a temperature gradient. Their thermoelectric power can reach tens of mV / K, which is 2 to 3 orders of magnitude higher than that of traditional electronic thermoelectric materials. However, ionic thermoelectric materials also face some limitations, mainly due to the singleness of thermoelectric behavior, that is, the material can only exhibit fixed p-type (positive thermoelectric power) or n-type (negative thermoelectric power) characteristics, and cannot dynamically switch polarity in situ in the same material system. This also greatly limits the acquisition of larger thermoelectric signals through pn series connection. In addition, due to the limitation that ions cannot enter the external circuit, ionic thermoelectric devices are difficult to output current continuously. Therefore, their main application scenarios are concentrated in the field of thermal sensing, but they still lack adaptability in intelligent systems that require temperature feedback.

[0004] With the rapid development of the Internet of Things (IoT) and smart wearable devices, the demand for thermal sensors has evolved from single-purpose temperature detection to multifunctional intelligent sensing. For example, in scenarios such as electronic skin overtemperature protection and industrial equipment thermal fault warning, sensors must exhibit nonlinear response characteristics—that is, trigger a characteristic signal at a specific critical temperature, thereby implementing a self-feedback protection mechanism. Traditional ionic thermoelectric materials, due to their monotonic thermoelectric behavior and only linear response to temperature changes, struggle to meet these intelligent requirements. While researchers have achieved similar functionality through external circuitry or algorithmic compensation, this significantly increases system complexity and energy consumption, deviating from the design trend of miniaturization and low power consumption. Furthermore, the development of highly sensitive heat flow detection devices urgently needs to break through the current technological limitations. While tandem pn thermoelectric cells can amplify the output signal, the fixed polarity of the material necessitates precise pre-arrangement of the p-type and n-type cells, resulting in low process tolerance. The development of ionic thermoelectric materials with intrinsic bipolar switching capabilities would simplify the device structure and simultaneously achieve signal multiplication through polarity reversal, providing a new solution for ultrasensitive detection.

[0005] In summary, there is an urgent need to develop smart materials with bipolar switchable thermoelectric properties. To address these challenges, the present invention proposes a pn-switchable thermoelectric ion gel based on LCST phase transition behavior. This technology achieves in-situ dynamic reversal of thermoelectric polarity through the material's intrinsic phase transition, breaking through the functional limitations of traditional ionic thermoelectric materials. This technology can be widely applied in the fields of intelligent thermal management and ultra-sensitive detection. In electronic devices, the pn-switching characteristics can instantly trigger overheat protection circuits, improving system reliability. In wearable devices, highly sensitive thermopiles can monitor micro-heat flux changes in the human body in real time for non-invasive health monitoring. In industrial scenarios, the nonlinear response characteristics can identify abnormal temperature rise patterns in equipment, enabling accurate fault diagnosis. Compared to existing technologies, the present invention combines high response sensitivity, intrinsic intelligence, and process compatibility, and is expected to promote the transition of thermoelectric materials from "passive sensing" to "active response," providing core technical support for smart energy, the Internet of Healthy Things, and Industry 4.0. Summary of the Invention

[0006] One objective of the present invention is to provide a method for preparing a thermally responsive smart ion gel. This thermal response is achieved through phase separation between a polymer network and an ionic liquid. Another objective of the present invention is to provide a method for in-situ thermoelectric reversal of the gel's properties, i.e., a change from p-type to n-type, based on phase separation, and to demonstrate the application of this mechanism in the construction of intelligent temperature sensors, i.e., highly sensitive sensors.

[0007] The specific scheme of the present invention is as follows:

[0008] The present invention provides a thermally responsive ionic liquid gel material, characterized in that the ionic liquid gel has a uniform polymer network structure and uses an ionic liquid as a dispersion medium. The polymer network is formed by cross-linking acrylate monomers, and the ionic liquid is composed of imidazole cations and hydrophobic anions.

[0009] The method for preparing the ion gel of the present invention is characterized by comprising the following steps:

[0010] The acrylic acid ester monomer and the ionic liquid are fully mixed in a certain proportion until uniform, to obtain a mixed solution A of the polymer monomer and the ionic liquid.

[0011] A crosslinking agent with a monomer molar content of 0.2 to 5% and a photoinitiator with a monomer molar content of 0.05 to 0.2% are added to solution A and mixed evenly to obtain a clear and transparent solution.

[0012] The obtained clear solution is transferred to an ultraviolet lamp for ultraviolet light-induced free radical polymerization to obtain an ionic liquid gel.

[0013] The structural formula of the acrylic acid ester monomer selected in step 1) is shown in (I), where 8≥m≥3.

[0014] Wherein, the structural formula of the ionic liquid selected in step 1) is shown as (II), 8≥n≥1.

[0015] Wherein, the mass ratio of the high molecular monomer to the ionic liquid in step 1) is 4:6-9:1.

[0016]

[0017] The organic crosslinking agent in step 2) is one or more crosslinking agents of the acrylate or acrylamide type, having the structural characteristics shown in (III), wherein p ≥ 1, q ≤ 5, R1 and R2 are independently hydrogen or an alkyl group with 1-5 carbon atoms.

[0018]

[0019] The photoinitiator described in step 2) is a 2,2-diethoxyacetophenone having the structural characteristics shown in (IV), wherein R1 and R2 are preferably alkyl groups with 1-8 carbon atoms.

[0020]

[0021] The wavelength and power of the ultraviolet light in step 3) are not particularly limited, preferably the ultraviolet light has a wavelength of 365 nm and a power range of 0.5 W / cm 2 ~10W / cm 2 The irradiation time is sufficient to complete the polymerization of the high molecular monomer, and the preferred irradiation time is 0.3-1.5 h.

[0022] In steps 1) and 2), those skilled in the art can prepare the ionic liquid gel prepolymer solution in a manner well known in the art.

[0023] In step 1), to obtain an ionic liquid gel material with good mechanical and optical properties, the preferred mass ratio of the polymer monomer to the ionic liquid is 4:6-7:3. In step 2), the amounts of the crosslinker and photoinitiator used are 1 / 1000-1 / 10 and 1 / 10000-5 / 1000 of the mass of the organic monomer, respectively.

[0024] The material prepared by the invention can realize in-situ pn conversion.

[0025] First, assembling multiple thermoelectric devices in series is a common approach to achieving higher sensitivity and higher thermoelectric signals. However, for ionic thermoelectric materials, p-type is more common, while n-type is relatively less reported. Therefore, assembling a single thermoelectric material (e.g., p-type) can only be achieved through an S-type assembly pattern, which poses significant challenges in device layout and routing, resulting in a low process error tolerance. In contrast, using both p-type and n-type thermoelectric components simultaneously can reduce process complexity through π-type connections. Furthermore, currently reported p- or n-type ionic thermoelectric materials are mostly achieved by varying the material ratio or electrode materials, making it impossible to achieve in situ p-n conversion within a given material system. Therefore, when amplifying the output signal by connecting pn thermoelectric units in series, the intrinsic heterogeneity of the p and n materials and the differences in electrode materials can lead to high and unstable contact impedance for the overall series device. Therefore, achieving in situ p-n conversion within the same material using external stimuli, without introducing electrode issues, is of great significance for the construction of intelligent devices based on thermoelectric materials and for simplifying the device structure of p- and n-series systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 .Optical photograph of the temperature-responsive reversible phase separation behavior of the prepared ion gel.

[0027] Figure 2 .Transition temperature test data of gel materials prepared under different ratio conditions.

[0028] Figure 3 It is an experimental device used to test the thermoelectric properties of gel.

[0029] Figure 4 .These are the optical photographs and thermoelectric performance data of ion gels in homogeneous and phase-separated states.

[0030] Figure 5 This is a comparison of the p-type and n-type thermoelectric performances of ion gels under different ratios.

[0031] Figure 6 It is intelligent temperature monitoring data based on in-situ bidirectional switchable thermoelectric ion gel.

[0032] Figure 7 This device is a highly sensitive temperature sensor based on a series connection of p- and n-type thermoelectric ion gels. (a) Schematic diagram of the device construction. (b) Device thermoelectric performance test diagram. (c) Device thermoelectric performance fitting. (d) Device application demonstration. DETAILED DESCRIPTION

[0033] Example 1

[0034] Preparation method of ion gel with thermally responsive reversible phase separation behavior:

[0035] 1) 0.6 g of butyl acrylate, 0.4 g of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 10 mg of ethylene glycol dimethacrylate, and 2 mg of 2,2-diethoxyacetophenone were uniformly mixed.

[0036] 2) The above solution was heated on a hot plate at 40° C. and magnetically stirred (5 to 10 min, 800 rpm) to mix the solution thoroughly to obtain a clear and transparent solution.

[0037] 3) The mixed solution was transferred to the target mold and irradiated under UV light for 30 minutes to fully polymerize. The UV light wavelength used was 365nm and the power was 5W / cm 2 The prepared ion gel has the property of thermal responsive phase separation, such as Figure 1 As shown, as the temperature increases, the gel transitions from a homogeneous, transparent state to a milky, phase-separated state. This phase separation behavior is driven by temperature-dependent hydrogen bonding, hydrophobic interactions, and electrostatic interactions between the anion and cations between the polymer network and the ionic liquid. In the homogeneous state, the polar components of the polymer backbone and the ionic liquid form strong hydrogen bonds. Furthermore, hydrophobic interactions exist between the side chains of the polymer network and the cationic alkane side chains. These interactions facilitate the solvation of the polymer network by the ionic liquid, resulting in a homogeneous, transparent gel. However, as the temperature increases, hydrogen bonding and hydrophobic interactions between the non-polar components are somewhat disrupted. When the interaction between the polymer and the ionic liquid becomes less pronounced than the electrostatic interactions between the anion and cations, the gel undergoes phase separation, forming a bicontinuous structure consisting of dense and sparse polymer regions, resulting in a milky, opaque appearance.

[0038] Example 2

[0039] Thermal responsive temperature regulation of ion gel materials:

[0040] 1) Different masses of butyl acrylate monomer (30, 40, and 50 wt%) were mixed with 1-propyl-3-methylimidazolium bistrifluoromethanesulfonyl imide ionic liquid (70, 60, and 50 wt%), ethylene glycol dimethacrylate (1% of the monomer content by molar ratio), and 2,2-diethoxyacetophenone (0.1% of the monomer content by molar ratio), respectively.

[0041] 2) The above solution was heated on a hot plate at 40° C. and magnetically stirred (5 to 10 min, 800 rpm) to mix the solution thoroughly to obtain a clear and transparent solution.

[0042] 3) Transfer the mixed solution to the target mold and place it under ultraviolet light for 30 minutes to fully polymerize into glue. The ultraviolet light wavelength used is 365nm and the power is 5W / cm 2。

[0043] 4) The ion gel prepared based on the above steps has different thermal response liquid-liquid phase separation transition temperatures. The specific phase transition temperature data are as follows: Figure 2 As shown in the figure, this is the transmittance data tested by a particle size analyzer. As the temperature rises, the gel changes from a uniform transparent state to a milky white phase separation state, and its transmittance gradually decreases from the initial 100% to 0%. The transition temperature is defined as the temperature corresponding to the transmittance decreasing to 80% of the initial state. Figure 2 As shown in FIG, as the polymer content in the gel increases from 30 wt% to 50 wt%, the transition temperature of the gel gradually increases, which are 47°C, 61°C and 81°C respectively.

[0044] Example 3

[0045] Preparation and testing characterization methods of temperature-responsive thermoelectric flip ion gel:

[0046] 1) 0.4 g of butyl acrylate, 0.6 g of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 10 mg of ethylene glycol dimethacrylate, and 2 mg of 2,2-diethoxyacetophenone were mixed.

[0047] 2) The above solution was heated on a hot plate at 40° C. and magnetically stirred (5 to 10 min, 800 rpm) to mix the solution thoroughly to obtain a clear and transparent solution.

[0048] 3) The mixed solution was transferred to the target mold and irradiated under UV light for 30 minutes to fully polymerize. The UV light wavelength used was 365nm and the power was 5W / cm 2 Prepare a long strip of gel material and place it on Figure 3 The device shown was prepared to characterize its thermoelectric performance.

[0049] 4) The phase transition temperature of the prepared gel material is 61°C, and the Figure 3 The temperature of the hot and cold ends of the device is set to be either all below or all above 61°C, and a temperature difference of 3.8°C is established between the hot and cold ends. Figure 4 As shown in Figure 2, when the total temperature of the established temperature difference is lower than the transition temperature of the gel material, the actual optical photos and thermoelectric test data are as follows: Figure 4 As shown in a. At this time, the gel is in a uniform and transparent state. Under a temperature difference of 3.8℃ between the hot and cold ends, it can produce p-type thermoelectric behavior (high potential on the low temperature side) with an amplitude of about 20mV. When the temperature setting for the temperature difference is increased to above the gel phase transition temperature, as shown in Figure 4As shown in Figure 2, the gel is milky white and opaque, indicating phase separation. At a 3.8°C temperature difference between the hot and cold ends, it exhibits n-type thermoelectric behavior (higher potential on the cold side) with an amplitude of approximately 8 mV.

[0050] Example 4

[0051] Bidirectional thermoelectric performance regulation of ion gel:

[0052] 1) Butyl acrylate and 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid were mixed in a mass ratio of 3:7, 4:6, 5:5, and 6:4. A crosslinker (ethylene glycol dimethacrylate) at a molar ratio of 1% and a photoinitiator (2,2-diethoxyacetophenone) at a molar ratio of 0.1% were added to the above solution.

[0053] 2) The above solution was heated on a hot plate at 40° C. and magnetically stirred (5 to 10 min, 800 rpm) to mix the solution thoroughly to obtain a clear and transparent solution.

[0054] 3) The mixed solution was transferred to the target mold and irradiated under UV light for 0.5 hours to fully polymerize. The UV light wavelength used was 365nm and the power was 5W / cm 2 The thermoelectric properties of ion gels prepared with different ratios were tested. The test results are as follows Figure 5 As shown in the figure, when the polymer content of the prepared gel is 30wt%, its p-type and n-type thermoelectric coefficients are ~8mV / K and -3.7mV / K, respectively. As the polymer content increases, the thermoelectric coefficients of both forms of ion gel decrease significantly. This is mainly because the thermoelectricity of ion gel mainly comes from the free diffusion of anions and cations in the gel. When the ionic liquid content decreases, the ion concentration in the gel decreases, resulting in a decrease in thermoelectric performance. In addition, when the polymer content increases, the density of the polymer network in the gel increases, which hinders the diffusion and migration of ions under the ion thermal field, causing its thermoelectric performance to decrease.

[0055] Example 5

[0056] Intelligent over-temperature protection sensor based on in-situ bidirectional switchable thermoelectric ion gel:

[0057] 1) 0.4 g of butyl acrylate, 0.6 g of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 10 mg of ethylene glycol dimethacrylate, and 2 mg of 2,2-diethoxyacetophenone were mixed.

[0058] 2) The above solution was heated on a hot plate at 40° C. and magnetically stirred (5-10 min, 800 rpm) to mix the solution thoroughly to obtain a clear and transparent solution.

[0059] 3) The mixed solution was transferred to the target mold and irradiated under UV light for 0.5 hours to fully polymerize. The UV light wavelength used was 365nm and the power was 5W / cm 2 The transition temperature of the ion gel is 61℃. Figure 3 The device shown in the figure tests its thermoelectric signal. The temperature of the hot end is gradually increased from room temperature to 90°C, while the temperature of the other side is not controlled. The temperature change is achieved through heat conduction between the gel material and the glass substrate. The test data is shown in the figure. Figure 6 As shown, the generated thermoelectric signal can be specifically divided into three stages. Stage 1: When the hot-end temperature is below 61°C, the gel is in a uniform and transparent state, exhibiting p-type thermoelectric characteristics. Its thermoelectric voltage gradually increases with the temperature difference between the gel sections. Stage 2: When the hot-end temperature is above the gel transition temperature of 61°C, while the cold-end temperature is below it, the two sides of the gel exhibit opposite thermoelectric characteristics: n-type on the hot side and p-type on the cold side. At this point, the thermoelectric voltage generated by the two sides gradually neutralizes, and the overall thermoelectric voltage no longer varies with temperature. Stage 3: The temperature continues to rise until the cold-end temperature exceeds the gel's phase transition temperature, causing the gel to completely transform into its original phase and exhibit n-type thermoelectric characteristics. At this point, further heating of the hot-end causes the thermoelectric voltage to reverse as the temperature difference between the two sides increases, thus gradually decreasing. This characteristic of the gel material makes it suitable for use in over-temperature protection sensors for critical components such as batteries and servers.

[0060] Example 6

[0061] Highly sensitive temperature sensor based on p-type and n-type thermoelectric ion gel series connection:

[0062] 1) Prepare two prepolymer solutions, A and B, respectively. Solution A: Mix 4 g of butyl acrylate, 6 g of 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 0.1 g of ethylene glycol dimethacrylate, and 20 mg of 2,2-diethoxyacetophenone. Solution B: Mix 5 g of butyl acrylate, 5 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 0.1 g of ethylene glycol dimethacrylate, and 20 mg of 2,2-diethoxyacetophenone.

[0063] 2) Heat the above solutions A and B separately on a hot plate at 40° C. and use magnetic stirring (5-10 min, 800 rpm) to fully mix the solutions to obtain clear and transparent solutions.

[0064] 3) The mixed solution was transferred to the target mold and irradiated under UV light for 15 minutes to fully polymerize. The UV light wavelength used was 365nm and the power was 5W / cm 2. We obtained ion gels A and B with transition temperatures of 61°C and 21°C, respectively. At room temperature (25°C), gels A and B exhibit homogeneous and phase-separated states, respectively, and the corresponding thermoelectric properties are p-type and n-type. In order to obtain higher sensitivity and thermoelectric signals, we assembled two gels with different thermoelectric properties with copper electrodes to prepare Figure 7 Schematic diagram a shows a 24-group series array (the 24 groups here have no special meaning, it is just a demonstration experiment to choose this number of series connections. Of course, more series connections will definitely get better performance). Figure 3 The device was used to test and characterize the array device, and its thermoelectric performance was as follows Figure 7 As shown in b, as the temperature difference increases from 0 to 6.8 °C, the thermovoltage increases almost linearly. By fitting the thermovoltage amplitudes under different temperature differences, we obtain Figure 7 The data shown in c indicates that the overall thermoelectric coefficient of the device is 0.22 V / K. Finally, the device was attached to an arm and generated an equilibrium voltage of approximately 0.25 V at room temperature (approximately 25°C). The temperature difference between the inside and outside of the device was approximately 1.1°C. These data demonstrate that by connecting p- and n-type gel devices in series, a temperature sensor with a large thermoelectric coefficient can be obtained, providing a material foundation and promising design ideas for the design and fabrication of wearable body temperature monitoring devices.

Claims

1. A method for preparing a thermally responsive intelligent ion gel for intelligent temperature sensing, characterized in that: The steps include: Step 1): mixing an acrylate monomer and an ionic liquid until uniform, wherein the acrylate monomer is hereinafter referred to as a monomer, to obtain a mixed solution A of the monomer and the ionic liquid; Step 2): adding a crosslinker having a monomer molar content of 0.2 to 5% and a photoinitiator having a monomer molar content of 0.05 to 0.2% to solution A and mixing them uniformly to obtain a clear and transparent solution; Step 3): transferring the obtained clear solution to ultraviolet light for ultraviolet light-induced free radical polymerization to obtain an ionic liquid gel; the illumination time is 0.3-1.5 hours; Wherein, the structural formula of the acrylic acid ester monomer selected in step 1) is as shown in formula (I), 8≥m≥3; Wherein, the structural formula of the ionic liquid selected in step 1) is as shown in formula (II), 8≥n≥1; Wherein, the mass ratio of the polymer monomer to the ionic liquid in step 1) is 4:6-9:1; The organic crosslinking agent in step 2) is one or more crosslinking agents of acrylate or acrylamide type, having the structural characteristics shown in formula (III); wherein p≥1, q≤5, R1 and R2 are independently hydrogen or alkyl with 1-5 carbon atoms; The photoinitiator in step 2) is 2,2-diethoxyacetophenone, having the structural characteristics shown in formula (IV), wherein R1 and R2 are alkyl groups with 1 to 8 carbon atoms; 2. The preparation method according to claim 1, wherein The wavelength and power of the ultraviolet light in step 3) are 365nm wavelength ultraviolet light with a power range of 0.5W / cm 2 ~10W / cm 2 .

3. The preparation method according to claim 1, wherein The mass ratio of monomer to ionic liquid is 4:6-7:3;.

4. The preparation method according to claim 1, wherein In step 2), the amounts of the crosslinking agent and the photoinitiator used are 1 / 1000-1 / 10 and 1 / 10000-5 / 1000 of the mass of the organic monomer, respectively.

5. An ion gel obtained by the preparation method according to any one of claims 1 to 4.

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