A thermoelectric self-generating gel fiber based on electrospinning and its preparation method

Abstract

This invention provides a thermoelectric self-generating gel fiber based on electrospinning and its preparation method, belonging to the field of thermoelectric materials. Addressing the application needs of thermoelectric materials, this invention uses polyvinylidene fluoride (PVDF) as the polymer raw material, prepares a spinning precursor solution of a certain mass concentration, and injects it into a syringe. During electrospinning, the electrospinning jet immediately enters a funnel-shaped collecting device after being ejected from the spinneret, forming oriented fibers along the airflow direction. Utilizing the rotation of the funnel and the stretching and twisting of the winder, highly oriented nanofiber bundles can be formed into continuous yarns. By adjusting the electrospinning parameters and optimizing the positions of the funnel collector, winder, and spinneret, the diameter of the nanofibers and yarns can be better controlled. After immersing the collected nanofiber yarn in different ionic liquid solutions for a period of time, it is removed to obtain conductive gel fibers, which can then be woven into thermoelectric fabrics, improving their Seebeck coefficient to a certain extent.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials, specifically relating to a thermoelectric self-generating gel fiber based on electrospinning and its preparation method. Background Technology

[0002] With the rapid development of artificial intelligence and the widespread adoption of smart terminals, wearable electronic devices present a huge market prospect. Flexible sensors, as the core component of man-made flexible electronic devices, have great application potential in fields such as human clinical diagnosis, health assessment, health monitoring, virtual electronics, flexible touchscreens, flexible electronic skin, and even industrial robots. A key technical challenge for wearable electronic devices lies in powering the various integrated electronic components, including flexible sensors. Current technologies mostly rely on external power supplies, which increases the burden on wearable electronic devices and is difficult to meet the needs of complex integrated smart wearable fabrics. Therefore, there is an urgent need to provide a fabric with efficient self-generating power capabilities to offer an effective way to power wearable electronic devices.

[0003] Thermoelectric materials are functional materials that can generate electricity by utilizing temperature differences in the environment. The Seebeck coefficient is a crucial parameter in the study of thermoelectric materials, measuring the thermal voltage generated by the material under a given temperature difference. Combining thermoelectric materials with textiles to create thermoelectric composite textiles allows for the continuous collection of electrical energy using the temperature difference between the human body and the surrounding environment, serving as flexible wearable energy-providing devices. Thermoelectric materials themselves are characterized by small size, safety, reliability, no pollution, no noise, and continuous energy collection. They impose no constraints on the wearer and are not limited by external environmental factors such as light, humidity, or wind, making them suitable for providing power to various low-energy electronic devices. This not only enables the wearability of thermoelectric materials but also the functionalization of textile materials, aligning with the major trends of energy conservation and sustainable development.

[0004] While existing fiber-based thermoelectric functional materials can generate their own electricity, the voltage output is limited and it is difficult to reach the operating voltage of flexible sensors to enable their operation. This is especially true for biochemical sensors, which have high operating voltage requirements. If the required operating voltage is not reached, it is difficult to catalyze the conversion of biochemical signals to electrical signals. Summary of the Invention

[0005] Ionic thermoelectric materials (such as polymer electrolytes and ionic liquids) possess Seebeck coefficients several orders of magnitude higher than those of semiconductor thermoelectric materials, enabling them to achieve higher open-circuit voltages and store electrical energy. The difference in thermophoretic mobility between positive and negative ions in the electrolyte is the source of the thermoelectricity generated by these materials. Therefore, effectively differentiating the selective migration of positive and negative ions under a thermal gradient is key to further improving the Seebeck coefficient of ionic thermoelectric materials. Highly oriented nanofibers can be fabricated using electrospinning technology. When the electrolyte permeates into the fibers and an axial temperature gradient is applied, the synergistic effect of the nanochannels formed between the nanofibers and the ion-polymer interaction leads to highly selective ion diffusion, thereby improving the Seebeck coefficient to some extent.

[0006] To address the shortcomings of existing technologies and the application requirements of thermoelectric materials, this invention uses polyvinylidene fluoride (PVDF) as the polymer raw material, prepares a spinning precursor solution of a certain mass concentration, and injects it into a syringe. During electrospinning, the electrospinning jet immediately enters the funnel-shaped collecting device after being ejected from the spinneret, and forms oriented fibers along the airflow direction. Utilizing the rotation of the funnel and the stretching and twisting of the winder, highly oriented nanofiber bundles can be formed into continuous yarns. By adjusting the electrospinning parameters (liquid feed rate, spinning voltage, receiving distance) and optimizing the positions of the funnel collector, winder, and spinneret, the diameter of the nanofibers and yarns can be better controlled.

[0007] The collected nanofiber yarns are soaked in different ionic liquid solutions for a period of time and then removed to obtain conductive gel fibers, which can then be woven into thermoelectric fabrics.

[0008] Beneficial Effects: This invention uses polyvinylidene fluoride (PVDF) as the polymer raw material and employs an electrospinning device with a funnel-shaped collection device to produce highly oriented nanofiber bundles and yarns. These are then immersed in different ionic liquid solutions to obtain gel fibers, which can be further woven into thermoelectric fabrics. Electrospinning technology can prepare highly oriented nanofibers. When an electrolyte permeates into the fibers and an axial temperature gradient is applied, the synergistic effect of the nanochannels formed between the nanofibers and the ion-polymer interaction leads to highly selective ion diffusion, thereby improving the Seebeck coefficient to a certain extent. Attached Figure Description

[0009] Figure 1 Schematic diagram of an electrospinning funnel-type receiver;

[0010] Figure 2 Microstructure of electrospun nanofibers with funnel as receiver;

[0011] Figure 3 Microstructure of electrospun nanofibers with rollers as receivers;

[0012] Figure 4 Microstructure of PVDF thin film;

[0013] Figure 5 This is a schematic diagram of the Seebeck coefficient testing system. Detailed Implementation

[0014] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of a thermoelectric self-generating gel fiber based on electrospinning and its preparation method, is provided by the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0015] Example 1

[0016] First, weigh a certain amount of polyvinylidene fluoride (PVDF, molecular weight 50w) powder, then add an appropriate mass of N,N-dimethylformamide (DMF) solvent. After stirring and dissolving at 40°C for 1 hour, prepare a solution with a mass fraction of 8wt%. Then, use an electrospinning apparatus equipped with a double-spinning system, a high-speed rotating funnel-shaped collecting device, and a yarn winder (see...). Figure 1 The nanofibers were prepared at 25°C and 50% humidity. The solution was injected into two 10mL syringes (7G needles). The syringes were placed on two feed pumps on either side, with a feed rate set to 0.7mL / h. The positive pressure spinning system voltage was +15kV, the negative pressure spinning system voltage was -5kV, the distance between the needles and the funnel was 13cm, the funnel rotation speed was 200r / min, and the yarn winder winding speed was 0.5m / min. The nanofiber yarn was collected after spinning was completed.

[0017] An acetone solution of 31 wt% ionic liquid EMIM:DCA was prepared, and the collected nanofiber yarns were immersed in it for 10 minutes before being removed to obtain gel fibers.

[0018] Example 2

[0019] First, a certain amount of polyvinylidene fluoride (PVDF, molecular weight 50w) powder was weighed, and then an appropriate amount of DMF solvent was added. After stirring and dissolving for 1 hour at 40℃, a solution with a mass fraction of 8wt% was prepared. The solution was prepared using an electrospinning apparatus equipped with a double spinning system, a high-speed rotating funnel-shaped collecting device, and a yarn winder, under conditions of 25℃ and 50% humidity. The solution was injected into two 10mL syringes with 7G needles. The syringes were placed on two feed pumps on either side, with the feed speed set to 0.7mL / h. The positive pressure spinning system voltage was +15kV, the negative pressure spinning system voltage was -5kV, the distance between the needles and the funnel was 13cm, the funnel rotation speed was 200r / min, and the yarn winder winding speed was 0.5m / min. After spinning was completed, the nanofiber yarn was collected.

[0020] An acetone solution of 31 wt% ionic liquid EMIM:TFSI was prepared, and the collected nanofiber yarns were immersed in it for 10 minutes before being removed to obtain gel fibers.

[0021] Example 3

[0022] First, a certain amount of polyvinylidene fluoride (PVDF, molecular weight 50w) powder was weighed, and then an appropriate amount of DMF solvent was added. After stirring and dissolving for 1 hour at 40℃, a solution with a mass fraction of 8wt% was prepared. The solution was prepared using an electrospinning apparatus equipped with a double spinning system, a high-speed rotating funnel-shaped collecting device, and a yarn winder, under conditions of 25℃ and 50% humidity. The solution was injected into two 10mL syringes with 7G needles. The syringes were placed on two feed pumps on either side, with the feed speed set to 0.7mL / h. The positive pressure spinning system voltage was +15kV, the negative pressure spinning system voltage was -5kV, the distance between the needles and the funnel was 13cm, the funnel rotation speed was 200r / min, and the yarn winder winding speed was 0.5m / min. After spinning was completed, the nanofiber yarn was collected.

[0023] An acetone solution of 31 wt% ionic liquid EMIM:BF4 was prepared, and the collected nanofiber yarns were immersed in it for 10 minutes before being removed to obtain gel fibers.

[0024] Example 4

[0025] First, a certain amount of polyvinylidene fluoride (PVDF, molecular weight 50w) powder was weighed, and then an appropriate amount of DMF solvent was added. After stirring and dissolving for 1 hour at 40℃, a solution with a mass fraction of 8wt% was prepared. The solution was prepared using an electrospinning apparatus equipped with a double spinning system, a high-speed rotating funnel-shaped collecting device, and a yarn winder, under conditions of 25℃ and 50% humidity. The solution was injected into two 10mL syringes with 7G needles. The syringes were placed on two feed pumps on either side, with the feed speed set to 0.7mL / h. The positive pressure spinning system voltage was +15kV, the negative pressure spinning system voltage was -5kV, the distance between the needles and the funnel was 13cm, the funnel rotation speed was 200r / min, and the yarn winder winding speed was 0.5m / min. After spinning was completed, the nanofiber yarn was collected.

[0026] A certain amount of Na:DCA was weighed and dissolved in an EMIM:DCA acetone solution (mass fraction 31 wt%), with a mass fraction of approximately 0.08 wt%. The collected nanofiber yarn was then immersed in the above solution for 10 minutes and removed to obtain gel fibers.

[0027] Comparative Example 1

[0028] First, a certain amount of polyvinylidene fluoride (PVDF, molecular weight 50w) powder was weighed out, and then an appropriate amount of DMF solvent was added. After stirring and dissolving for 1 hour at 40℃, a solution with a mass fraction of 8wt% was prepared. Electrospinning was then performed using a roller as the receiving device. Under conditions of 25℃ and 50% humidity, a high voltage of 15 / -5kV was applied between the needle and the receiver. The spinning gap was adjusted to 15cm, the liquid supply rate was 0.7ml / h, and the receiver rotation speed was 200r / min. After spinning, a nanofiber film was formed.

[0029] An acetone solution of 31 wt% ionic liquid EMIM:DCA was prepared, and the collected nanofiber film was immersed in it for 10 minutes before being removed to obtain a gel film.

[0030] Comparative Example 2

[0031] First, a certain amount of polyvinylidene fluoride (PVDF, molecular weight 50w) powder was weighed out, and then an appropriate amount of DMF solvent was added. After stirring and dissolving at 40°C for 1 hour, a solution with a mass fraction of 8wt% was prepared. The solution was then uniformly spin-coated (3000 r / min, 20 s) onto a clean glass slide, and then placed in a constant temperature vacuum drying oven for 3 hours to allow the solvent to completely evaporate and form a thin film. The film was then immersed in an acetone solution (mass fraction 31wt%) of the ionic liquid EMIM:DCA for 10 minutes and then removed to obtain the final conductive gel film.

[0032] The morphology of the PVDF fibers and films collected in Example 1 and Comparative Examples 1 and 2 were observed using a cold field scanning electron microscope, as follows: Figures 2-4 As shown: The SEM image of Example 1 shows highly oriented nanofibers with an average diameter of approximately 510 nm. The SEM image of Comparative Example 1 shows disordered nanofiber distribution with an average diameter of approximately 260 nm. The SEM image of Comparative Example 2 shows a micron-scale porous structure on the film surface, presumably due to solvent evaporation.

[0033] Based on the preliminary work, the following methods were adopted: Figure 5 The self-built testing system shown tests the Seebeck coefficient of gel fibers and films. The temperature at both ends of the sample is controlled by a Pallet patch, the open-circuit voltage across the sample is measured using a Keithley 2400 digital source meter, and the real-time temperature at both ends is acquired using an infrared imager. The Seebeck coefficient is then calculated.

[0034] The Seebeck coefficient of the materials prepared in Examples 1-4 and Comparative Examples 1 and 2 was tested to verify or understand their performance. The test results are shown in Table 1 below.

[0035] Table 1. Seebeck coefficient test results

[0036] Seebeck coefficient mV / K 6.1 -5.6 3.6 7.0 4.5 4.1

[0037] The Seebeck coefficient test results from Examples 1-4 show that the gel fibers prepared from EMIM:DCA, EMIM:BF4, and a mixed electrolyte of EMIM:DCA and Na:DCA all have positive Seebeck coefficients, indicating they are P-type semiconductors. The difference in value is mainly due to the different interactions between the negative ions and PVDF molecules. The gel fibers prepared from EMIM:TFSI have negative Seebeck coefficients, indicating they are N-type semiconductors. Comparing the Seebeck coefficient test results with Comparative Examples 1 and 2, it can be found that the orientation distribution of the nanofibers is more conducive to the difference in thermophoretic mobility between positive and negative ions, ultimately resulting in a higher Seebeck coefficient.

[0038] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing thermoelectric self-generating nanofiber yarn, characterized in that, Includes the following steps: Polyvinylidene fluoride (PVDF) was dissolved in N,N-dimethylformamide (DMF) to form an 8 wt% solution. This solution was then spun using an electrospinning apparatus equipped with a dual-spinning system, a high-speed rotating funnel-shaped collecting device, and a yarn winder to obtain nanofiber yarn. The nanofiber yarn was then immersed in an ionic liquid solution for 10 minutes and removed to obtain conductive gel fibers. The ionic liquid solution included acetone solutions of ionic liquids EMIM:DCA, EMIM:TFSI, and BF4, or EMIM:DCA acetone solutions containing dissolved Na:DCA. The positive pressure spinning system voltage was +15 kV, and the negative pressure spinning system voltage was -5 kV. The funnel rotation speed was 200 r / min, and the yarn winding speed was 0.5 m / min. The solution was injected into two 10 mL syringes with 7 G needles. The syringes were placed on the feed pumps on both sides, and the feed speed was set to 0.7 mL / h. The distance between the two needles and the funnel was 13 cm. During spinning, the temperature was 25 °C and the humidity was 50%. Highly oriented nanofibers were prepared by electrospinning. When the ionic liquid electrolyte permeated into the fiber and an axial temperature gradient was applied, the synergistic effect of the nanochannels formed between the nanofibers and the ion-polymer interaction led to highly selective ion diffusion, thereby improving its Seebeck coefficient to a certain extent.

2. Nanofiber yarn prepared by the preparation method of claim 1.

3. Conductive gel fiber prepared using the nanofiber yarn described in claim 2.

4. A thermoelectric fabric woven using the conductive gel fiber described in claim 3.

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