Liquid metal functional phase polyurethane-based dielectric fiber membrane, preparation method and application thereof

Abstract

The application discloses a liquid metal functional phase polyurethane-based dielectric fiber membrane and a preparation method and application thereof, and relates to the field of electrospinning process and dielectric composite materials. The fiber membrane (LM / TPU-Fiber) of the application is prepared by using an electrospinning process, so that the liquid metal is non-uniformly distributed in the polyurethane. The structure of the fiber membrane is a spindle connected by fine fibers, wherein the spindles of the polyurethane fibers are rich in a large amount of liquid metal, and the fine fibers serving as supporting and connecting functions contain less liquid metal. The application uses an electrospinning auxiliary process to prepare a polyurethane fiber membrane with a liquid metal content of up to 90vol%, and the fiber membrane has a low dielectric constant and does not have the percolation phenomenon generally existing under high filler filling. The fiber membrane can be widely applied in the fields of capacitive pressure sensors, energy storage polymers, phase change materials and the like.

Description

Technical Field

[0001] This invention relates to the field of electrospinning technology and dielectric composite materials, specifically to a polyurethane-based dielectric fiber membrane with a liquid metal functional phase, its preparation method, and its application. Background Technology

[0002] Liquid metal (LM) is a metal with high electrical conductivity that flows at room temperature. Compared to rigid fillers, LM exhibits extremely high fluidity, effectively reducing the modulus mismatch between functional materials and the matrix in flexible composites. Currently, LM is widely used in the field of flexible dielectric composites, and it has been proven that LM can improve the dielectric constant of the dielectric without causing large dielectric losses. However, high LM content (>80 vol%) can cause dielectric composites to transform into conductive composites, i.e., percolation occurs. Therefore, obtaining high-LM-content dielectric composites is crucial. The traditional method for preparing high-LM-content fibers is coaxial wet spinning, using LM as the core material and polymer as the shell material to obtain high-LM-content fibers. However, the core in this core-shell structure is conductive, so this fiber is usually used in conductive composites. Currently, there is no effective method to fill the fiber interior of a fiber membrane with a large amount of LM (>80 vol%) without causing the composite to transform into a conductive composite.

[0003] Electrospinning is a highly efficient technique for preparing nanofiber membranes. This method involves spraying a polymer solution under a high-voltage electric field, causing droplets to form Taylor cones under the influence of the electric field and then extend into fine filaments, thereby producing nanoscale polymer fibers. Electrospinning-prepared fiber membranes possess high specific surface area and tunable porosity, thus finding wide applications in filtration, sensing, and drug delivery. The morphology and size of the fiber membrane can be controlled by adjusting parameters such as polymer concentration, solution type, voltage, and spinning rate. However, due to the extremely high surface tension and low viscosity of liquid metal (LM), it is difficult to directly spin it during electrospinning. Currently, the preparation of high-content LM dielectric fiber membranes remains a challenge, requiring overcoming the inherent characteristics of LM. Furthermore, in the field of composite materials, controlling the non-uniform distribution configuration of functional phases is also a difficult task, with limited related reports. Summary of the Invention

[0004] This invention provides a polyurethane-based dielectric fiber membrane with a liquid metal functional phase, its preparation method, and its applications, aiming to solve the problem in existing technologies where dielectric composites based on liquid metal (LM) transform into conductive composites at high LM content. This method utilizes an electrospinning-assisted process to help form a high-content LM in a polyurethane (TPU) solution, achieving for the first time a TPU fiber membrane with an LM volume fraction as high as 90%. Through electrospinning, the TPU solution forms coarse and fine fibers with spindle structures. The spindle structures are enriched with a large number of LM droplets, which play a role in regulating the dielectric constant. In the fine fibers, the LM content is lower, serving a traction and support function. The separation of the spindle structures results in an isolated, non-uniform distribution of LM in the TPU fiber membrane. Due to the non-uniform distribution of LM and the special structure of the fiber membrane, this fiber membrane retains the properties of a dielectric material and does not transform into a conductive composite, thus solving the percolation problem in high-content LM composites. This polyurethane-based dielectric fiber membrane with a liquid metal functional phase has broad application potential. It can be used in fields such as capacitive pressure sensors, energy storage polymers, and phase change materials, providing high-performance dielectric materials for these applications.

[0005] According to the purpose of this invention, the present invention first provides a method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase, comprising the following steps:

[0006] 1) Add liquid metal to a mixed solution of acetone and N,N-dimethylformamide and treat with ultrasound in an ice-water bath;

[0007] 2) Add polyurethane to the liquid metal dispersion obtained in step 1) and heat and stir to obtain a spinning solution;

[0008] 3) The spinning solution obtained in step 2) is loaded into a syringe for electrospinning to obtain a thin film;

[0009] 4) Dry the film obtained in step 3) at room temperature to obtain a polyurethane-based dielectric fiber film with liquid metal functional phase.

[0010] As a preferred embodiment of the present invention, the parameters used in step 1) of the ice-water bath ultrasonic treatment are an ultrasonic power of 270-540W and a treatment time of 10-60min. As a preferred embodiment of the present invention, the parameters used in the ice-water bath ultrasonic treatment are a power of 360W and a treatment time of 60min.

[0011] As a preferred embodiment of the present invention, the mass ratio of acetone to N,N-dimethylformamide in the mixed solution in step 1) is 8:5.

[0012] As a preferred embodiment of the present invention, the liquid metal is one or more of gallium indium alloy, gallium indium tin alloy, and gallium tin alloy.

[0013] In a preferred embodiment of the present invention, the polyurethane added in step 2) is added in an amount of 25% to 35 wt% of the mixed solution of acetone and N,N-dimethylformamide. In another preferred embodiment, the polyurethane accounts for 30% of the mass fraction of the solvents acetone and N,N-dimethylformamide.

[0014] As a preferred embodiment of the present invention, the liquid metal accounts for ≤90% of the volume fraction of the polyurethane-based dielectric fiber membrane.

[0015] In a preferred embodiment of the present invention, the electrospinning parameters in step 3) are: spinning rate of 1-3 mL / h, needle size of 17-23G, distance between collector and needle of 12-18 cm, and voltage of 12-15 kV. In another preferred embodiment of the present invention, the electrospinning parameters are: spinning rate of 2 mL / h, needle size of 23G, collector distance of 15 cm, and voltage of 12 kV.

[0016] The present invention also provides a polyurethane-based dielectric fiber membrane with a liquid metal functional phase prepared by the above method.

[0017] As a preferred embodiment of the present invention, the liquid metal accounts for 80-90% of the volume fraction of the polyurethane-based dielectric fiber membrane.

[0018] This invention further provides the application of polyurethane-based dielectric fiber membranes with the liquid metal functional phase, wherein the fiber membranes are filled with up to 90 vol% LM in the dielectric composite material without percolation and have a low dielectric constant. This solves the problem of transforming high-content conductive functional phase composite materials from dielectric composites to conductive composites, and can be used as dielectric layers in the fabrication of capacitive pressure sensors, or as energy storage polymers or phase change materials.

[0019] Compared with the prior art, the beneficial effects and innovations of this invention are as follows:

[0020] (1) This invention utilizes electrospinning-assisted technology for the first time. Based on the principle of isolated cluster non-uniform distribution, LM is confined in TPU fibers. This achieves the effect of no percolation at a LM content of up to 90 vol% in dielectric composite materials, solving the problem of transforming high-content conductive functional phase composite materials from dielectric composite materials to conductive composite materials.

[0021] (2) The fiber prepared by the present invention has a spindle structure, which contains a large amount of LM and a small amount of LM in the fine fibers connecting the spindle. This structure realizes the isolated cluster type non-uniform distribution of LM. The electrospinning-assisted process used in the present invention provides a new method for the preparation of isolated cluster type non-uniform distribution composite materials.

[0022] (3) The raw materials used in this invention are simple in composition and low in cost, consisting only of liquid metal, polyurethane, acetone, and N,N-dimethylformamide solvent. Furthermore, the prepared fiber membrane can be recycled using organic solvents, making it environmentally friendly. The simple process, involving only three steps—ultrasound, stirring, and electrospinning—highly simplifies the preparation process of fiber membranes with high LM content. Attached Figure Description

[0023] Figure 1 Here is a SEM image of the TPU fiber membrane in Comparative Example 1;

[0024] Figure 2 The image shows a scanning electron microscope (SEM) image of a TPU fiber membrane with LM accounting for 10 vol% in Example 1.

[0025] Figure 3 SEM image of the TPU fiber membrane with LM accounting for 90 vol% in Example 2;

[0026] Figure 4 The dielectric constant and dielectric loss factor of TPU fiber films with different volume fractions of LM are measured. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0028] The technical problem to be solved by this invention is to provide a method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase, achieving an isolated cluster-type non-uniform distribution of LM, which can prevent percolation and transformation into a conductive composite material even when the LM volume fraction is as high as 90%, thus remaining a dielectric composite material. Furthermore, this preparation process is simple, low-cost, and recyclable.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents and materials used in the following examples are all commercially available.

[0030] Example 1:

[0031] A method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase includes the following steps:

[0032] 1) Add 0.226 mL of Ga:In alloy (mass ratio Ga:In = 3:1) liquid metal LM to 10 mL of a mixed solution of acetone and N,N-dimethylformamide (mass ratio 8:5) and treat with an ultrasonic cell disruptor at 360 W for 60 min in an ice-water bath.

[0033] 2) Add 2.53g of polyurethane TPU to the liquid metal dispersion obtained in step 1) and heat and stir thoroughly;

[0034] 3) The spinning solution obtained in step 2) is loaded into a syringe for electrospinning. The spinning rate is 2 mL / h, the needle type is 23G, the distance between the collector and the needle is 15 cm, and the voltage is 12 kV.

[0035] 4) Dry the film obtained in step 3) at room temperature.

[0036] The sample was named LM / TPU-Fiber-10.

[0037] Example 2:

[0038] A method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase includes the following steps:

[0039] 1) Add 18.306 mL of Ga:In alloy (mass ratio Ga:In = 3:1) liquid metal LM to 10 mL of a mixed solution of acetone and N,N-dimethylformamide (mass ratio 8:5) and treat with an ultrasonic cell disruptor at 360 W for 60 min in an ice-water bath.

[0040] 2) Add 2.53g of polyurethane TPU to the liquid metal dispersion obtained in step 1) and heat and stir thoroughly;

[0041] 3) The spinning solution obtained in step 2) is loaded into a syringe for electrospinning. The spinning rate is 2 mL / h, the needle type is 23G, the distance between the collector and the needle is 15 cm, and the voltage is 12 kV.

[0042] 4) Dry the film obtained in step 3) at room temperature.

[0043] The sample was named LM / TPU-Fiber-90.

[0044] Comparative Example 1:

[0045] This example is a comparative sample. Except for omitting step 1) and not adding LM, the other steps are the same as in Example 1.

[0046] The sample was named TPU-Fiber.

[0047] Comparative Example 2:

[0048] This example serves as a comparative sample. The preparation method of a 70 vol% liquid metal polyurethane film includes the following steps:

[0049] 1) Add 4.746 mL of Ga:In alloy (mass ratio Ga:In = 3:1) liquid metal LM to 10 mL of a mixed solution of acetone and N,N-dimethylformamide (mass ratio 8:5) and treat with an ultrasonic cell disruptor at 360 W for 60 min in an ice-water bath.

[0050] 2) Add 2.53g of polyurethane TPU to the liquid metal dispersion obtained in step 1) and heat and stir thoroughly;

[0051] 3) Pour the dispersion obtained in step 2) directly into the mold and dry it in an oven at 80°C for 24 hours to obtain a liquid metal polyurethane film, named LM / TPU-Film-70.

[0052] Comparative Example 1 of this invention is a pure TPU electrospun fiber membrane without LM, from the attached Figure 1 As can be seen, the TPU-Fiber fibers have a uniform diameter, no obvious spindle shape, and a smooth surface. However, the SEM image of Example 1 (attached) Figure 2 In Example 2, 10 vol% LM was added to the spinning solution. The resulting LM / TPU-Fiber-10 fiber membrane exhibited fibers of varying thickness. The brighter, round dots represent LM fibers, while the straight lines represent TPU fibers. It was observed that the thicker fibers contained a higher LM content, while the finer fibers contained very little LM. (SEM image of LM / TPU-Fiber-90 in Example 2 is attached.) Figure 3 The coarse and fine fibers are more distinct, exhibiting a spindle shape. Laminated filaments (LMs) are abundant within the spindle, while fewer are found in the fine fibers. This non-uniform distribution of LMs is achieved using an electrospinning-assisted process. These spindles can be viewed as isolated clusters of LMs, with the fine fibers acting as tension supports. SEM images demonstrate that the method provided in this invention effectively achieves this isolated cluster-type non-uniform distribution.

[0053] This invention provides applications for the liquid metal / polyurethane fiber membrane prepared above, in the field of dielectric composite materials, whose dielectric constant and dielectric loss factor are as shown in the appendix. Figure 4As shown, the dielectric constant of LM / TPU-Fiber-10 in Example 1 is 1.78, and the dielectric loss factor is 0.0174; the dielectric constant of LM / TPU-Fiber-90 in Example 2 is 2.52, and the dielectric loss factor is 0.0130; the dielectric constant of TPU-Fiber in Comparative Example 1 is 1.36, and the dielectric loss factor is 0.00829. It can be seen that even with up to 90 vol% LM-filled TPU fiber membranes, percolation did not occur. As a dielectric composite material, it can be used in fields such as the dielectric layer of capacitive pressure sensors, energy storage polymers, and phase change materials. However, liquid metal polyurethane-based composite materials prepared without the method provided by this invention would be conductive films at high LM content. Due to the large density difference between LM and the polyurethane matrix causing LM sedimentation, the lower surface conductivity of LM / TPU-Film-70 in Comparative Example 2 is 213 S / m. At this content, the film has begun to transform into a conductive composite material, and the conductive film no longer has concepts such as dielectric constant.

[0054] While preferred embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase, characterized in that, Includes the following steps: 1) Add liquid metal to a mixed solution of acetone and N,N-dimethylformamide and treat with ultrasound in an ice-water bath; 2) Add polyurethane to the liquid metal dispersion obtained in step 1) and heat and stir to obtain a spinning solution; 3) The spinning solution obtained in step 2) is loaded into a syringe for electrospinning to obtain a thin film; 4) Dry the film obtained in step 3) at room temperature to obtain a polyurethane-based dielectric fiber film with a liquid metal functional phase; The parameters used in step 1) ice water bath ultrasonic treatment are ultrasonic power 270~540 W and time 10~60 min. The mass ratio of acetone to N,N-dimethylformamide in the mixed solution in step 1) is 8:5; The electrospinning parameters in step 3) are: spinning rate 1~3 mL / h, needle size 17~23 G, distance between collector and needle 12~18 cm, and voltage 12~15 kV. The liquid metal accounts for 80-90% of the volume fraction of the polyurethane-based dielectric fiber membrane.

2. The method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase according to claim 1, characterized in that... The liquid metal is one or more of gallium-indium alloy, gallium-indium-tin alloy, and gallium-tin alloy.

3. The method for preparing a polyurethane-based dielectric fiber membrane with a liquid metal functional phase according to claim 1, characterized in that... The amount of polyurethane added in step 2) is 25% to 35 wt% of the mixed solution of acetone and N,N-dimethylformamide.

4. A polyurethane-based dielectric fiber membrane with a liquid metal functional phase prepared by the method according to any one of claims 1-3.

5. The application of the polyurethane-based dielectric fiber membrane with liquid metal functional phase as described in claim 4, characterized in that, The fiber membrane is used as a dielectric layer to prepare a capacitive pressure sensor, or as an energy storage polymer or phase change material.

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