PVDF (Polyvinylidene Fluoride) / Ca-POM (Polyoxymethylene) composite fiber membrane, preparation method thereof and application of PVDF / Ca-POM composite fiber membrane in preparation of wearable flexible piezoelectric sensor

Abstract

The invention discloses a PVDF / Ca-POM composite fiber membrane, a preparation method thereof and application of the PVDF / Ca-POM composite fiber membrane in preparation of a wearable flexible piezoelectric sensor, and belongs to the technical field of functional materials. The composite fiber membrane is prepared from PVDF (Polyvinylidene Fluoride) and Ca-POM (Polyoxymethylene) through electrochemical spinning. PVDF has piezoelectricity, and Ca-POM has high flexibility and a high length-diameter ratio; double networks can be formed between the PVDF and the Ca-POM, and the existence of the Ca-POM restrains the movement of a PVDF chain, so that the mechanical property of the composite material is further improved; meanwhile, due to the high dipole moment effect between Ca-POM and PVDF, the conformation of a PVDF chain can be changed, the relative content of a beta phase can be increased, the piezoelectric property of the composite material is effectively improved, the sensitivity of the composite material serving as a wearable flexible piezoelectric sensor is guaranteed, and therefore the composite material has important application prospects in the field of wearable flexible piezoelectric sensors.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and specifically relates to a PVDF / Ca-POM composite fiber membrane, a preparation method thereof, and an application thereof in the preparation of a wearable flexible piezoelectric sensor. Background Art

[0002] Polyvinylidene fluoride (PVDF) is a highly non-reactive thermoplastic fluorinated polymer. It is a class of flexible polymers with piezoelectric properties. It can be used as engineering plastics, used to prepare corrosion-resistant sealing rings and capacitors, and also used as coatings, insulating materials, and ion exchange membrane materials. Increasing the content of β phase in PVDF is the fundamental reason for improving its piezoelectric properties. The use of PVDF to prepare wearable flexible piezoelectric sensors requires not only excellent piezoelectric properties but also excellent mechanical properties. However, due to the plasticity of PVDF, the mechanical properties of the wearable flexible piezoelectric sensors prepared by it are poor. Therefore, it is of great significance to develop wearable flexible piezoelectric sensors with simple and safe processes, high mechanical properties and piezoelectric properties. Summary of the invention

[0003] The invention provides a PVDF / Ca-POM composite fiber membrane, wherein the composite fiber membrane comprises PVDF and Ca-POM.

[0004] The above PVDF / Ca-POM composite fiber membrane is prepared by the following method:

[0005] The PVDF is dissolved in a solvent and stirred evenly to obtain a PVDF precursor solution; then Ca-POM is added and stirred evenly to obtain a PVDF / Ca-POM composite material; the PVDF / Ca-POM composite material is subjected to electrochemical spinning to obtain a PVDF / Ca-POM composite fiber membrane after spinning.

[0006] In the above preparation method, each raw material is selected from the following parts:

[0007] PVDF 0.25-1.25 parts, solvent 3-3.75 parts, Ca-POM 0.25-1 part;

[0008] When the component is a solid component, the portion number represents grams; when the component is a liquid component, the portion number represents milliliters; in actual applications, the portion number can be enlarged or reduced in proportion to the portion number.

[0009] In a specific embodiment, each raw material is selected from the following parts:

[0010] PVDF 1 part, solvent 3.5 parts, Ca-POM 0.5 parts;

[0011] When the component is a solid component, the portion number represents grams; when the component is a liquid component, the portion number represents milliliters; in actual applications, the portion number can be enlarged or reduced in proportion to the portion number.

[0012] In the above preparation method, the solvent is selected from one or more of DMF, acetone, tetrahydrofuran, and N-methylpyrrolidone; preferably DMF.

[0013] In the above preparation method, the temperature during the dissolution process is selected from 50 to 90°C, preferably 70°C.

[0014] In the above preparation method, the spinning parameters of the electrochemical spinning are selected from: flow rate of 0.01-0.1 mL / min, voltage of 15-30 kV, and receiving distance of 10-20 cm; preferably: flow rate of 0.05 mL / min, voltage of 25 kV, and receiving distance of 15 cm.

[0015] In the above preparation method, the Ca-POM is prepared by the following method:

[0016] Dissolve phosphotungstic acid hydrate and calcium nitrate tetrahydrate in water, stir until no precipitation occurs, then add 1-octadecene and oleylamine, stir and react; after the reaction is completed, wash the product to obtain Ca-POM.

[0017] In the above-mentioned preparation method of Ca-POM, the components are selected from the following parts:

[0018] 0.5-2 parts of phosphotungstic acid hydrate, 0.05-0.2 parts of calcium nitrate tetrahydrate, 10-20 parts of water, 10-20 parts of 1-octadecene, 1-5 parts of oleylamine;

[0019] When the component is a solid component, the portion number represents grams; when the component is a liquid component, the portion number represents milliliters; in actual applications, the portion number can be enlarged or reduced in proportion to the portion number.

[0020] The present invention provides an application of the above-mentioned PVDF / Ca-POM composite fiber membrane in the preparation of a wearable flexible piezoelectric sensor.

[0021] The present invention provides a wearable flexible piezoelectric sensor, which is assembled from a PVDF / Ca-POM composite fiber film, a copper foil tape, a polyimide tape, and a copper wire with polished ends.

[0022] The beneficial effects of the present invention are:

[0023] The present invention uses PVDF as an organic phase and Ca-POM as an inorganic phase to prepare a PVDF / Ca-POM composite fiber membrane. PVDF has piezoelectricity, and Ca-POM has high flexibility and high aspect ratio; a double network can be formed between PVDF and Ca-POM, and the presence of Ca-POM constrains the movement of the PVDF chain, further improving the mechanical properties of the composite material; at the same time, the high dipole moment effect between Ca-POM and PVDF can change the conformation of the PVDF chain, increase the relative content of the β phase, effectively improve the piezoelectric performance of the composite material, and ensure its sensitivity as a wearable flexible piezoelectric sensor. In addition, the preparation method of the present invention is simple and low in cost. The piezoelectric constant (d33) of the PVDF / Ca-POM composite fiber membrane is 93.63pm / V, the Young's modulus can reach 3.0MPa, and the elongation is 88%, which is consistent with the Young's modulus and elongation of human skin; thus, it has important application prospects in the field of wearable flexible piezoelectric sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the SEM image of PVDF / Ca-POM composite material;

[0025] Figure 2 It is the SEM image of PVDF / Ca-POM composite fiber membrane;

[0026] Figure 3 is the tensile stress-strain curve of PVDF / Ca-POM composite fiber membrane;

[0027] Figure 4 is the relative content of β phase in PVDF / Ca-POM composite fiber membrane;

[0028] Figure 5 It is the piezoelectric cycle test curve of PVDF / Ca-POM composite fiber membrane;

[0029] Figure 6 This is a physical picture of a wearable flexible piezoelectric sensor;

[0030] Figure 7 Sensing attempt for wearable flexible piezoelectric sensor. DETAILED DESCRIPTION

[0031] In the present invention, polyvinylidene fluoride is referred to as PVDF; calcium-phosphotungstate sub-nanowire is referred to as Ca-POM; N,N-dimethylformamide is referred to as DMF. DMF is used as a solvent in the present invention to provide a liquid environment for the reaction system. It does not participate in the reaction itself and its use amount is reasonable.

[0032] The calcium-phosphotungstate sub-nanowire (Ca-POM) used in the present invention is prepared by the following method:

[0033] 1g of phosphotungstic acid hydrate and 0.123g of calcium nitrate (tetrahydrate) were dissolved in 16mL of deionized water to obtain a clear solution without precipitation. After stirring for 10min, 12mL of 1-octadecene and 4mL of oleylamine were added in sequence and stirred for 8h. The product was washed with ethanol and octane and centrifuged three times to obtain calcium-phosphotungstate sub-nanowires.

[0034] Other materials used in the present invention, if not otherwise stated, can be obtained through commercial channels. Other terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those of ordinary skill in the art. The present invention is further described in detail below in conjunction with specific examples and with reference to data. The following examples are only for illustrating the present invention, and are not intended to limit the scope of the present invention in any way.

[0035] Example 1

[0036] The steps for preparing PVDF / Ca-POM composite fiber membrane are as follows:

[0037] 1 g PVDF was dissolved in 3.5 mL DMF solution at 70 °C and stirred for 4 h to obtain a uniform PVDF precursor solution; then 0.5 g Ca-POM was added to the PVDF precursor solution at a mass ratio of 1:0.5 and stirred evenly to obtain a PVDF / Ca-POM composite material; an electrospinning machine (Qingdao Sibening Intelligent Equipment Co., Ltd., SNZJ-1400) was used to electrochemically spin the PVDF / Ca-POM composite material, and the spinning parameters were: flow rate of 0.05 mL / min, voltage of 25 kV, and receiving distance of 15 cm; after spinning, a PVDF / Ca-POM composite fiber membrane was obtained.

[0038] According to tests, the relative content of β phase in the PVDF / Ca-POM composite fiber membrane of this embodiment is 97.9%.

[0039] Example 2

[0040] The steps for preparing PVDF / Ca-POM composite fiber membrane are as follows:

[0041] 1 g PVDF was dissolved in 3.75 mL DMF solution at 70 °C and stirred for 4 h to obtain a uniform PVDF precursor solution; then 0.25 g Ca-POM was added to the PVDF precursor solution at a mass ratio of 1:0.25 and stirred evenly to obtain a PVDF / Ca-POM composite material; an electrospinning machine (Qingdao Sibening Intelligent Equipment Co., Ltd., SNZJ-1400) was used to electrochemically spin the PVDF / Ca-POM composite material, and the spinning parameters were: flow rate of 0.05 mL / min, voltage of 25 kV, and receiving distance of 15 cm; after spinning, a PVDF / Ca-POM composite fiber membrane was obtained.

[0042] According to tests, the relative content of β phase in the PVDF / Ca-POM composite fiber membrane of this embodiment is 89.5%.

[0043] Example 3

[0044] The steps for preparing PVDF / Ca-POM composite fiber membrane are as follows:

[0045] 1 g PVDF was dissolved in 3.25 mL DMF solution at 70 °C and stirred for 4 h to obtain a uniform PVDF precursor solution; then 0.75 g Ca-POM was added to the PVDF precursor solution at a mass ratio of 1:0.75 and stirred evenly to obtain a PVDF / Ca-POM composite material; an electrospinning machine (Qingdao Sibening Intelligent Equipment Co., Ltd., SNZJ-1400) was used to electrochemically spin the PVDF / Ca-POM composite material, and the spinning parameters were: flow rate of 0.05 mL / min, voltage of 25 kV, and receiving distance of 15 cm; after spinning, a PVDF / Ca-POM composite fiber membrane was obtained.

[0046] According to tests, the PVDF / Ca-POM composite fiber membrane of this embodiment has a relative content of β phase of 92.7%.

[0047] Example 4

[0048] The steps for preparing PVDF / Ca-POM composite fiber membrane are as follows:

[0049] 1 g PVDF was dissolved in 3 mL DMF solution at 70 °C and stirred for 4 h to obtain a uniform PVDF precursor solution; then 1 g Ca-POM was added to the PVDF precursor solution at a mass ratio of 1:1 and stirred evenly to obtain a PVDF / Ca-POM composite material; an electrospinning machine (Qingdao Sibening Intelligent Equipment Co., Ltd., SNZJ-1400) was used to electrochemically spin the PVDF / Ca-POM composite material, and the spinning parameters were: flow rate of 0.05 mL / min, voltage of 25 kV, and receiving distance of 15 cm; after spinning, a PVDF / Ca-POM composite fiber membrane was obtained.

[0050] According to tests, the relative content of β phase in the PVDF / Ca-POM composite fiber membrane of this embodiment is 69.9%.

[0051] Comparative Example

[0052] The steps for preparing PVDF fiber membrane are as follows:

[0053] 1 g of PVDF was dissolved in 4 mL of DMF solution at 70 °C and stirred for 4 h to obtain a uniform PVDF precursor solution. The PVDF precursor solution was electrochemically spun using an electrospinning machine (Qingdao Sibening Intelligent Equipment Co., Ltd., SNZJ-1400). The spinning parameters were: flow rate of 0.05 mL / min, voltage of 25 kV, and receiving distance of 15 cm. After spinning, a PVDF fiber membrane was obtained.

[0054] According to tests, the relative content of β phase in the PVDF / Ca-POM composite fiber membrane of this embodiment is 43.6%.

[0055] 1. SEM image

[0056] The SEM images of the PVDF / Ca-POM composite material and the PVDF / Ca-POM composite fiber membrane in Example 1 were measured. Figure 1 and Figure 2 As shown:

[0057] SEM images of PVDF / Ca-POM composites are shown in Figure 1 As shown: an interwoven grid structure appears in the composite material, indicating the existence of a double network structure.

[0058] SEM images of PVDF / Ca-POM composite fiber membrane Figure 2 As shown: the diameter of the PVDF / Ca-POM composite fiber membrane is about 0.39 μm, and the orientation and arrangement of the PVDF / Ca-POM composite fiber membrane are more orderly, thereby making the composite fiber membrane more stable.

[0059] 2. Tensile stress

[0060] The mechanical strength of the PVDF / Ca-POM composite fiber membrane described in Example 1 and the PVDF fiber membrane described in the comparative example was measured using an electronic universal testing machine (Jinan Quanli Testing Technology Co., Ltd., CTS-E5). The tensile measurement was performed uniaxially at a tensile rate of 50 mm / min. The tensile test specimen was dumbbell-shaped, 20 mm long, 10 mm wide inside, and 2 mm thick.

[0061] Test results such as Figure 3 As shown:

[0062] The upper curve is Example 1, and the lower curve is a comparative example. The PVDF / Ca-POM composite fiber membrane has a more excellent tensile fracture stress and can withstand a higher tensile stress under the same tensile strain. According to the rising slope of the curve and the area under the curve, the PVDF / Ca-POM composite fiber membrane also has a higher elastic modulus and toughness.

[0063] 3. Relative content of β phase

[0064] PVDF is an incompletely crystalline organic ferroelectric material. Semi-crystalline PVDF has five different crystal phase structures, namely α, β, γ, δ, and ε. Among these crystal phases, the β phase has the highest dipole moment, can form spontaneous polarization, and has piezoelectricity. The FT-IR data of PVDF / Ca-POM composite fiber membrane was measured using Fourier transform infrared spectrometer (FT-IR), and the relative content of β phase in PVDF / Ca-POM composite fiber membrane was calculated based on the FT-IR test results and Lambert-Beer law.

[0065] Test results such as Figure 4 As shown:

[0066] The PVDF / Ca-POM composite fiber membrane has the highest relative content of β phase, which reaches 97.9%. Compared with the PVDF fiber membrane, it is increased by nearly 124.5%. The increase in the relative content of β phase indicates that the PVDF / Ca-POM composite fiber membrane has excellent piezoelectricity.

[0067] 4. Piezoelectric performance

[0068] Prepare Ca-POM / PVDF composite fiber membrane electrode, cut the Ca-POM / PVDF composite fiber membrane of Example 1 into 5cm×5cm size, cut the commercial double-sided conductive copper platinum tape into 5cm×5cm size and paste it on the upper and lower surfaces of the Ca-POM / PVDF composite fiber membrane, and use the polished copper wires at both ends to lead out the electrodes on both sides for easy connection to the two ends of the Keithley 2450 digital source meter, and use commercial polyimide tape for packaging. Use Mark-10 to apply a fixed pressure to test the electrical signal response of the Ca-POM / PVDF composite fiber membrane pressure, and the applied pressure is 20N.

[0069] Test results such as Figure 5 As shown:

[0070] The PVDF / Ca-POM composite fiber membrane has an excellent response process. Under a pressure of 20N, as the movement occurs, the PVDF / Ca-POM composite fiber membrane stably outputs signals and has excellent piezoelectric properties.

[0071] The above test results show that the relative content of β phase of the PVDF / Ca-POM composite fiber membrane prepared in Example 1 is 97.9%, and the piezoelectric constant (d 33 ) is 93.63pm / V, Young's modulus is 3.0MPa, and elongation is 88%, which are consistent with the Young's modulus and elongation of human skin.

[0072] Application Examples

[0073] To prepare a wearable flexible piezoelectric sensor, the steps are as follows:

[0074] The PVDF / Ca-POM composite fiber membrane of Example 1 was used to assemble and prepare a wearable flexible piezoelectric sensor; wherein the Ca-POM / PVDF composite fiber membrane was cut into a size of 5cm×5cm, and the commercial double-sided conductive copper platinum tape was cut into a size of 5cm×5cm and pasted on the upper and lower surfaces of the Ca-POM / PVDF composite fiber membrane. The polished copper wires at both ends led out the electrodes on both sides for easy connection to the electrochemical workstation, and the commercial polyimide tape was used for packaging. The actual picture of the prepared wearable flexible piezoelectric sensor is as follows: Figure 6 shown.

[0075] Sensor test:

[0076] The assembled wearable flexible piezoelectric sensors are fixed to the fingers, elbows, wrists, throat, knees, and soles of the feet to detect the changes in piezoelectric signals generated when they move.

[0077] Test results such as Figure 7 As shown:

[0078] The PVDF / Ca-POM composite fiber membrane wearable flexible piezoelectric sensor produces different pressure output signals as the above-mentioned human body parts bend to different degrees and make sounds. It can detect multiple tiny signals generated during human body movement and has extremely high sensing performance.

[0079] The above test results show that the wearable flexible piezoelectric sensor prepared by the present invention can detect signals transmitted by human body movements at multiple locations such as fingers, elbows, wrists, throat, knees, and soles of feet.

[0080] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A PVDF / Ca-POM composite fiber membrane, characterized in that: The composite fiber membrane comprises PVDF and Ca-POM.

2. The method for preparing the PVDF / Ca-POM composite fiber membrane according to claim 1, characterized in that: The steps include: The PVDF is dissolved in a solvent and stirred evenly to obtain a PVDF precursor solution; then Ca-POM is added and stirred evenly to obtain a PVDF / Ca-POM composite material; the PVDF / Ca-POM composite material is subjected to electrochemical spinning to obtain a PVDF / Ca-POM composite fiber membrane after spinning.

3. The preparation method according to claim 2, characterized in that: The raw materials are selected from the following parts: PVDF 0.25-1.25 parts, solvent 3-3.75 parts, Ca-POM 0.25-1 part.

4. The preparation method according to claim 2, characterized in that: The solvent is selected from one or more of DMF, acetone, tetrahydrofuran and N-methylpyrrolidone.

5. The preparation method according to claim 2, characterized in that: The temperature during the dissolution process is selected from 50 to 90°C.

6. The preparation method according to claim 2, characterized in that: The spinning parameters of the electrochemical spinning are selected from: flow rate of 0.01-0.1 mL / min, voltage of 15-30 kV, and receiving distance of 10-20 cm.

7. The preparation method according to claim 2, characterized in that: The Ca-POM is prepared by the following method: Dissolve phosphotungstic acid hydrate and calcium nitrate tetrahydrate in water, stir until no precipitation occurs, then add 1-octadecene and oleylamine, stir and react; after the reaction is completed, wash the product to obtain Ca-POM.

8. The preparation method according to claim 7, characterized in that: The ingredients are selected from the following quantities: 0.5-2 parts of phosphotungstic acid hydrate, 0.05-0.2 parts of calcium nitrate tetrahydrate, 10-20 parts of water, 10-20 parts of 1-octadecene, and 1-5 parts of oleylamine.

9. Use of the PVDF / Ca-POM composite fiber membrane according to claim 1 or the PVDF / Ca-POM composite fiber membrane prepared by the method according to any one of claims 2 to 8 in the preparation of a wearable flexible piezoelectric sensor.

10. A wearable flexible piezoelectric sensor, characterized in that: It is assembled from PVDF / Ca-POM composite fiber membrane, copper foil tape, polyimide tape and copper wire with polished ends.

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