Molecular piezoelectric / pvdf composite piezoelectric nanofiber for sensing and preparation method thereof

Abstract

The application discloses a kind of molecular piezoelectric body / PVDF composite sensing piezoelectric nanofiber and its preparation method, belong to functional composite material technical field.The mixture of certain amount-of-substance ratio of organic amine ligand (AC) and metal halide (MX) is added to the organic mixed solvent containing N, N-dimethylformamide (DMF), and shaken at room temperature until the mixture is completely dissolved.Then, different portions of PVDF are added, and a colorless transparent mixed solution is obtained after continuous stirring.The solution is then spun using an electrospinning machine to obtain white colorless nanofiber.The nanofiber is prepared in situ by one-step method, with low energy consumption and high piezoelectric phase content.The nanofiber fully utilizes the excellent piezoelectricity of molecular piezoelectric body and PVDF composite material, and has outstanding energy harvesting performance and sensing ability.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials technology, and relates to a molecular piezoelectric / PVDF nanocomposite material and its preparation method. Background Technology

[0002] Piezoelectric materials are a class of materials with non-centrosymmetric crystal structures that can convert mechanical energy into electrical energy (direct piezoelectric effect) and electrical energy into mechanical energy (inverse piezoelectric effect). This property makes them widely used in high-voltage power supplies, sensors, ultrasonic transducers, energy harvesters, and other fields. Currently, the most widely used commercial piezoelectric materials are inorganic piezoelectric materials, which have advantages such as chemical stability, excellent piezoelectric properties, and high dielectric constant. However, they often have disadvantages such as difficulty in forming films, poor mechanical flexibility, and the presence of toxic elements.

[0003] Molecular piezoelectrics are a promising type of piezoelectric material that has been developed in recent years. Due to their excellent solution-forming properties, tunable structure, and low-cost synthesis, they have broad application prospects in energy harvesting and sensors. Since 2017, research on the piezoelectric properties of organic-inorganic hybrid molecular piezoelectrics has progressed rapidly, and they have now surpassed commercially available inorganic piezoelectric ceramics in terms of piezoelectric strain coefficient and piezoelectric voltage coefficient. For example, the reported d... 33 The values ​​are 185 and 220 pC / N, respectively, comparable to commercially available piezoelectric ceramics. However, organic-inorganic hybrid molecular piezoelectrics are typically linked by coordination bonds, resulting in lower mechanical strength and chemical stability. These properties reduce the duration and reliability of molecular piezoelectrics under periodic mechanical stimulation.

[0004] With the development of modern flexible electronics, piezoelectric materials are required to be thin, soft, and lightweight to fully realize their applications in flexible self-powered sensors and energy harvesting. These requirements pose a significant challenge to both traditional inorganic piezoelectric ceramics and emerging molecular piezoelectrics, as they often exhibit extremely poor mechanical flexibility. Although the traditional polymeric piezoelectric material polyvinylidene fluoride (PVDF) has overcome these problems to some extent, the complex fabrication process and temporal instability of high-β-phase PVDF remain bottlenecks hindering its further development. Considering the molecular hybridization characteristics and excellent piezoelectricity of organic-inorganic hybrid molecular piezoelectrics, their composite with PVDF will generate a two-phase interaction. This not only facilitates the control of the PVDF crystal structure transition from the α-phase to the β-phase but also enables a synergistic effect on piezoelectric properties. Therefore, using molecular piezoelectrics and PVDF to prepare high-voltage composite nanofibers via electrospinning will greatly promote the application of these two types of piezoelectric materials in the field of self-powered flexible sensing. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems of existing materials and technologies, and to provide a molecular piezoelectric / PVDF composite piezoelectric nanofiber material for sensing with high β phase content. At the same time, it provides a method for preparing the material. The molecular piezoelectric in the obtained molecular piezoelectric / PVDF composite piezoelectric nanofiber for sensing is grown in situ inside PVDF, and its scale is nanoscale in all three dimensions.

[0006] The composite piezoelectric nanofiber material of this invention is composed of two piezoelectric materials: a molecular piezoelectric material formed by the coordination of an organic amine ligand (AC) and a metal halide (MX), and PVDF. This material exhibits excellent piezoelectric properties and performs exceptionally well in flexible sensing and energy harvesting applications. This invention utilizes organic amine ligands (AC), metal halides (MX), and PVDF as raw materials, employing electrospinning and in-situ growth processes of the molecular piezoelectric material. This process is time-efficient, energy-saving, and a green, environmentally friendly, and simple preparation method.

[0007] Furthermore, the organic amine ligand AC is one or more of trimethylchloromethylamine, trimethylchloroethylamine, and 3-chloro-1-(N,N-dimethyl)propylamine. Preferably, the organic amine ligand is trimethylchloromethylamine (TMCM).

[0008] Furthermore, the metal halide MX is one or more combinations of ZnX2, AlX3, RuX3, CdX2, SnX4, CuX2, AgX, and SbX3, wherein X is one of F, Cl, Br, and I. Preferably, the metal halide is CdCl2.

[0009] Furthermore, the diameter of the composite nanofibers is less than or equal to 1.0 μm, and the diameter of the molecular piezoelectric is less than 18 nm.

[0010] The present invention provides a method for preparing the above-described molecular piezoelectric / PVDF composite piezoelectric nanofiber material for sensing: molecular piezoelectric nanocrystals are directly grown inside PVDF in situ; electrospinning is used to induce the interaction and bonding between the piezoelectric material and PVDF molecules; and the formation of the β phase (piezoelectric phase) of PVDF is induced simultaneously during nanofiber preparation. The specific steps are as follows:

[0011] Step 1: Add a mixture of organic amine ligand AC and metal halide MX to an organic mixed solution containing N,N-dimethylformamide DMF at a certain molar ratio, and sonicate at room temperature to dissolve the mixture to obtain solution A;

[0012] The molar ratio of the selected organic amine ligand AC to the metal halide MX is 1:0.25–1:4; preferably, the molar ratio is 1:1.

[0013] The DMF-containing organic mixed solution is composed of the following components: Component 1: DMF; Component 2: one or more of methanol, ethanol, acetone, formaldehyde, acetaldehyde, glacial acetic acid, and N-methylpyrrolidone.

[0014] The organic mixed solution containing DMF consists of component one being pure DMF solvent, or component one being mixed with component two in a volume ratio of 1:1 to 1:4 to form the solvent. Preferably, a mixed solution of DMF and acetone in a volume ratio of 1:1 is selected.

[0015] Step 2: Add PVDF powder to solution A, heat and stir for a certain period of time to obtain a clear solution B with a certain viscosity.

[0016] The organic amine ligand AC and the metal halide MX have a mass ratio of 0–15% of the PVDF mass. Preferably, the organic amine ligand AC and the metal halide MX have a mass ratio of 3% of the PVDF mass.

[0017] The stirring process uses a rotation speed of 300–900 r / min, a temperature of 40–60℃, and a time of 4–24 h. Preferably, the stirring speed is 600 r / min, the temperature is 60℃, and the time is 12 h.

[0018] Step 3: Place the clarified solution B into a syringe, install an electrospinning needle, and spin the nanofibers at a certain injection speed under a certain high voltage electric field. Use a roller with a certain rotation speed to receive the nanofibers and obtain composite piezoelectric nanofibers.

[0019] The potential difference of the electric field in electrospinning is 9–19 kV, and the rotational speed of the receiving roller is 100–1000 r / min. Preferably, the voltage of the high-voltage electric field is selected as 15 kV, and the rotational speed of the roller is selected as 700 r / min.

[0020] Step 4: Perform final drying on the composite piezoelectric nanofibers from Step 3 to remove residual solvent, and obtain molecular piezoelectric / PVDF composite piezoelectric nanofibers for sensing.

[0021] The present invention discloses the following technical effects:

[0022] This invention utilizes a solution containing an organic amine ligand (AC), an inorganic ligand (metal halide MX), and PVDF to grow nanoscale nanocrystals in situ via electrospinning. By leveraging the interactions between these nanocrystals and PVDF molecules, as well as electrostatic interactions, PVDF composite nanofibers with a high β-phase are obtained, exhibiting excellent piezoelectricity. Flexible devices fabricated from these nanofiber mats exhibit polarization on the surface of the piezoelectric element and the β-phase of PVDF within the mat when periodic external forces are applied, resulting in charge accumulation. A certain voltage and current can be monitored using oscilloscopes, current amplifiers, and other equipment. When the external force is removed, the crystals return to an uncharged state. This voltage and current, generated by external excitation, can not only be harvested as energy, but the magnitude of the electrical signal also varies with the external stimulus, enabling the sensing of human activity of varying intensities. This demonstrates that the molecular piezoelectric / PVDF composite piezoelectric nanofibers prepared in this invention have significant application potential in the fields of energy harvesting and sensing.

[0023] This invention involves room-temperature preparation, in-situ growth of piezoelectric materials, and one-step formation of PVDF composite nanofibers. It has advantages such as simple operation, short time cycle, and low production energy consumption. It is an excellent method for obtaining PVDF nanocomposites with high β content, laying the foundation for the development and application of novel flexible electronic materials. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is an optical photograph of the molecular piezoelectric / PVDF composite nanofiber of Example 1 of the present invention.

[0026] Figure 2 The image shows the morphology (left) and radial scale distribution (right) of the molecular piezoelectric / PVDF composite nanofibers of Example 1 of this invention.

[0027] Figure 3 The distribution and size (left, white spots) and scale distribution (right) of TMCM-CdCl3 inside PVDF fibers in Example 1 of the present invention are shown.

[0028] Figure 4 This is a comparison of the phase purity of pure PVDF nanofibers and molecular piezoelectric / PVDF composite nanofibers in Example 1 of the present invention.

[0029] Figure 5 The images show the FT-IR (left) and DSC melting curve (right) of the molecular piezoelectric / PVDF composite nanofibers of Example 1 of this invention.

[0030] Figure 6 The piezoelectric output voltage (left) and current density (right) of the molecular piezoelectric / PVDF composite nanofibers in Example 1 of this invention are shown.

[0031] Figure 7 The molecular piezoelectric / PVDF composite nanofiber of Embodiment 1 of the present invention is used as a sensing device to detect the instantaneous output voltage of human activity. Detailed Implementation

[0032] The molecular piezoelectric / PVDF composite piezoelectric nanofiber material of this invention requires no complex preparation process or long material growth cycle. It is prepared in situ in a one-step method using mixed raw materials. Compared to other types of PVDF composite materials, it eliminates the need for subsequent stretching, annealing, and other methods to obtain high β-phase PVDF composite materials, making it a simple, efficient, and environmentally friendly approach.

[0033] Example 1:

[0034] Preparation of piezoelectric nanofibers for sensing based on molecular piezoelectric / PVDF composite: (1) Weigh equal amounts of trimethylchloromethylamine (TMCM-Cl) and cadmium chloride (CdCl3) and place them in a 20ml sample bottle. Add a certain amount of a mixed solution of N,N-dimethylformamide and acetone and sonicate until clear. (2) Add a certain amount of PVDF powder to the clear solution and stir rapidly on a magnetic stirrer for 12h. Let it stand for 12h for later use. (3) Add the settled mixed solution to a 1ml syringe, install a microporous needle on the syringe, and place the syringe in the high voltage field of an electrospinning machine. (4) Adjust the advance speed of the syringe and the magnitude of the electric field of the electrospinning machine to spin the nanofibers and obtain a nanofiber mat composed of a large number of nanofibers interwoven together, such as Figure 1 As shown.

[0035] The surface morphology of the nanofiber mat was observed using field emission scanning electron microscopy (FE-SEM), and the results are as follows: Figure 2 As shown, the nanofiber felt is composed of a large number of intricately interwoven nanofibers, exhibiting a porous network structure in its microstructure, with the nanofibers operating at the nanometer scale in the radial direction. Statistical analysis at the radial scale revealed that approximately 83% of the fibers have a diameter between 200 nm and 500 nm.

[0036] The size and distribution of molecular piezoelectrics inside the nanofibers were observed using transmission electron microscopy (TEM), and the results are as follows: Figure 3As shown, the molecular piezoelectrics grow and crystallize in situ within the nanofibers, exhibiting a uniform distribution and no obvious agglomeration. Furthermore, the molecular piezoelectrics are nanoscale, with nearly 70% of the particles ranging in size from 4 nm to 10 nm.

[0037] X-ray diffraction (XRD) was used to characterize the nanofibers and determine their phase structure. Here, the XRD patterns of pure PVDF nanofibers and those of molecular piezoelectric / PVDF composite nanofibers with optimized processing were compared. The results are as follows: Figure 4 As shown, the composite nanofibers prepared by this invention, compared to pure PVDF nanofibers, are almost entirely composed of β-phase structures, while pure PVDF nanofibers exhibit a coexistence of α and β phases. This demonstrates that the method of this invention can induce the transformation of PVDF from a non-piezoelectric α-phase to a piezoelectric β-phase, thereby obtaining PVDF materials with a high β-phase content.

[0038] Quantitative analysis of the piezoelectric phase of the composite nanofibers was performed using Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The results are as follows: Figure 5 As shown. Through the α phase at 763 cm⁻¹ -1 Peak intensity and β phase at 840 cm⁻¹ -1 The peak intensity at a certain point was used to calculate the β-phase content in the crystalline phase of the composite nanofibers using a formula, yielding a β-phase content of approximately 90%. Further analysis using the endothermic enthalpy of the first melting point obtained by DSC revealed the crystallinity of the composite nanofibers to be approximately 81%.

[0039] The piezoelectric output performance of molecular piezoelectric / PVDF composite piezoelectric nanofibers was evaluated using a self-designed piezoelectric testing device. The applied force of the testing device was 5N, and the frequency was 10Hz. The results are as follows: Figure 6 As shown. The piezoelectric nanofibers of this invention can generate a peak voltage of approximately 22V and a current density of 1.1μA / cm. 2 It can be harvested as electrical energy. In addition, the output characteristics of the electrical signal are that the peak value of the positive electrical signal is approximately equal to the peak value of the negative electrical signal, and the frequency of the electrical signal is consistent with the frequency of the applied force.

[0040] Example 2:

[0041] Preparation of piezoelectric nanofibers for sensing based on molecular piezoelectric / PVDF composite: (1) Weigh equal amounts of 3-chloro-1-(N,N-dimethyl)propylamine (DPA-Cl) and cadmium chloride (CdCl3) into a 20ml sample bottle, add a 5:5 mixture of N,N-dimethylformamide and acetone, and sonicate until clear; (2) Add a certain amount of PVDF powder to the clear solution so that the total mass of DPA-Cl and CdCl3 in the solution is 10% of the mass of PVDF. Then stir rapidly on a magnetic stirrer for 24h, and let stand for 12h for later use; (3) Add the standing mixed solution into a 1ml syringe, install a microporous needle on the syringe, and place the syringe in the high voltage electric field of an electrospinning machine; (4) Adjust the advance speed of the syringe and the magnitude of the electric field of the spinning machine to spin, and obtain a nanofiber mat composed of a large number of nanofibers intertwined.

[0042] Example 3:

[0043] Preparation of piezoelectric nanofibers for sensing by molecular piezoelectric / PVDF composite: (1) Weigh equal amounts of trimethylchloroethylamine (TMCE-Cl) and cadmium chloride (CdCl3) and place them in a 20ml sample bottle. Add a 3:7 mixture of N,N-dimethylformamide and acetone and sonicate until clear. (2) Add a certain amount of PVDF powder to the clear solution so that the total mass of TMCE-Cl and CdCl3 in the solution is 5% of the mass of PVDF. Then stir rapidly on a magnetic stirrer for 12h and let stand for 12h for later use. (3) Add the standing mixed solution to a 1ml syringe, install a microporous needle on the syringe, and place the syringe in the high voltage electric field of an electrospinning machine. (4) Adjust the advance speed of the syringe and the magnitude of the electric field of the spinning machine to spin, and obtain a nanofiber mat made of a large number of nanofibers intertwined.

[0044] Example 4:

[0045] Preparation of piezoelectric nanofibers for sensing based on molecular piezoelectric / PVDF composite: (1) Weigh equal amounts of trimethylchloromethylamine (TMCM-Cl) and ferric bromide (FeBr3) into a 20ml sample bottle, add a mixed solution of N,N-dimethylformamide and acetone in a ratio of 8:2, and sonicate until clear; (2) Add a certain amount of PVDF powder to the clear solution so that the total mass of TMCM-Cl and FeBr3 in the solution is 5% of the mass of PVDF. Then stir rapidly on a magnetic stirrer for 12h, and let stand for 12h for later use; (3) Add the standing mixed solution into a 1ml syringe, install a microporous needle on the syringe, and place the syringe in the high voltage electric field of an electrospinning machine; (4) Adjust the advance speed of the syringe and the magnitude of the electric field of the spinning machine to spin, and obtain a nanofiber mat composed of a large number of nanofibers intertwined.

[0046] Example 5:

[0047] Preparation of piezoelectric nanofibers for sensing based on molecular piezoelectric / PVDF composite: (1) Weigh equal amounts of trimethylchloromethylamine (TMCM-Cl) and tin tetrachloride (SnCl4) and place them in a 20ml sample bottle. Add a 5:5 mixture of N,N-dimethylformamide and acetone and sonicate until clear. (2) Add a certain amount of PVDF powder to the clear solution so that the total mass of TMCM-Cl and SnCl4 in the solution is 10% of the mass of PVDF. Then stir rapidly on a magnetic stirrer for 12h and let stand for 12h for later use. (3) Add the standing mixed solution to a 1ml syringe, install a microporous needle on the syringe, and place the syringe in the high voltage field of an electrospinning machine. (4) Adjust the advance speed of the syringe and the magnitude of the electric field of the spinning machine to spin the nanofibers and obtain a nanofiber mat made of a large number of nanofibers intertwined.

[0048] Application example:

[0049] Fabrication of flexible sensors based on nanofibers: (1) Cut piezoelectric nanofiber felt into a specific shape and cut metal conductive cloth matching its size as top and bottom electrodes; (2) Bond the metal conductive cloth to the top and bottom of the fiber felt with conductive adhesive, and remove the gap between the conductive cloth and the fiber felt by repeated scraping method, and then attach wires to the conductive cloth; (3) Encapsulate the device with PET tape or silicone electronic encapsulation liquid to obtain a flexible electronic device with a sandwich structure.

[0050] Flexible sensing devices can be fabricated using piezoelectric nanofibers composed of molecular piezoelectric elements and PVDF composites to monitor human activity. For example, placing the sensing device in the palm of a person's hand can monitor their clapping movements, with results such as... Figure 7 As shown, an adult's clapping can be converted into an electrical signal by a sensor, which can then detect the force and frequency of the clapping.

[0051] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a molecular piezoelectric / PVDF composite piezoelectric nanofiber for sensing, characterized in that, The piezoelectric nanofibers are formed in situ within the PVDF matrix by organic amine ligand AC and metal halide MX, thereby inducing the formation of molecular piezoelectric / PVDF composite nanofibers with high β phase content, achieving the combined effect of the two piezoelectric phases, molecular piezoelectric and PVDF. This method involves directly growing molecular piezoelectric nanocrystals inside PVDF through in-situ growth, and simultaneously inducing the formation of the β phase in PVDF while preparing nanofibers via electrospinning. The specific steps are as follows: Step 1: Add a mixture of organic amine ligand AC and metal halide MX to an organic mixed solution containing N,N-dimethylformamide DMF at a certain molar ratio, and sonicate at room temperature to dissolve the mixture to obtain solution A; Step 2: Add PVDF powder to solution A, heat and stir for a certain period of time to obtain a clear solution B with a certain viscosity; Step 3: Place the clarified solution B into a syringe, install an electrospinning needle, and spin the nanofibers at a certain injection speed under a certain high voltage electric field. Use a roller with a certain rotation speed to receive the nanofibers and obtain composite piezoelectric nanofibers. Step 4: Dry the composite piezoelectric nanofibers obtained in Step 3 to remove residual solvent and obtain molecular piezoelectric / PVDF composite piezoelectric nanofibers for sensing. The organic amine ligand AC is one or more of trimethylchloromethylamine, trimethylchloroethylamine, and 3-chloro-1-(N,N-dimethyl)propylamine; The metal halide MX is one or more of ZnX2, AlX3, RuX3, CdX2, SnX4, CuX2, AgX, and SbX3, wherein X is one of F, Cl, Br, and I.

2. The method for preparing the molecular piezoelectric / PVDF composite piezoelectric nanofibers for sensing according to claim 1, characterized in that, The aforementioned organic mixed solution containing N,N-dimethylformamide (DMF) comprises the following components: Component 1: DMF; Component 2: A mixture of one or more of the following: methanol, ethanol, acetone, formaldehyde, acetaldehyde, glacial acetic acid, and N-methylpyrrolidone; The solvent is formed by mixing component one (DMF pure solvent) or component one to component two in a volume ratio of 1:1–1:

4.

3. The method for preparing the molecular piezoelectric / PVDF composite piezoelectric nanofibers for sensing according to claim 1, characterized in that, The selected organic amine ligand AC and metal halide MX have a molar ratio of 1:0.25–1:

4. The selected organic amine ligand AC and metal halide MX have a mass of 0–15% of the PVDF mass.

4. The method for preparing the molecular piezoelectric / PVDF composite piezoelectric nanofibers for sensing according to claim 1, characterized in that, In step two, the stirring process uses a speed of 300–900 r / min, a temperature of 40–60℃, and a time of 4–24 h.

5. The method for preparing the molecular piezoelectric / PVDF composite piezoelectric nanofibers for sensing according to claim 1, characterized in that, The potential difference of the electric field in electrospinning is 9–19 kV, and the rotational speed of the receiving roller is 100–1000 r / min.

6. A molecular piezoelectric / PVDF composite piezoelectric nanofiber for sensing, characterized in that, The piezoelectric nanofibers prepared by the method described in any one of claims 1-5 have a diameter of less than or equal to 1.0 μm, and the molecular piezoelectric bodies have a diameter of less than 18 nm.

7. The use of the molecular piezoelectric / PVDF composite piezoelectric nanofiber for sensing according to claim 6, characterized in that, It can be used as a sensor to detect human activity and as an energy harvester to collect mechanical energy.

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