CN115991937B

CN115991937B - Stretchable piezoelectric film, preparation method thereof and stretchable ultrasonic transducer

Info

Publication number: CN115991937B
Application number: CN202310297576.8A
Authority: CN
Inventors: 任丹阳; 尹永刚; 高大; 施钧辉; 王钰琪; 陈睿黾; 李驰野
Original assignee: Zhejiang Lab
Current assignee: Zhejiang Lab
Priority date: 2023-03-23
Filing date: 2023-03-23
Publication date: 2023-07-18
Anticipated expiration: 2043-03-23
Also published as: CN115991937A

Abstract

The invention relates to a stretchable piezoelectric film, a preparation method thereof and a stretchable ultrasonic transducer. The stretchable piezoelectric film comprises an elastic matrix, a polymer carrier and inorganic piezoelectric phase particles loaded on the polymer carrier, wherein a flexible three-dimensional network structure is formed among the inorganic piezoelectric phase particles through the polymer carrier, and the elastic matrix is filled in pores of the flexible three-dimensional network structure. The stretchable piezoelectric film disclosed by the invention has the characteristics of excellent stretchability, piezoelectric performance, electromechanical coupling performance and low acoustic impedance, so that the stretchable piezoelectric film can be directly used for preparing an ultrasonic transducer, and the prepared ultrasonic transducer has excellent stretchability and piezoelectric performance.

Description

Stretchable piezoelectric film, preparation method thereof and stretchable ultrasonic transducer

Technical Field

The invention relates to the technical field of piezoelectric materials, in particular to a stretchable piezoelectric film, a preparation method thereof and a stretchable ultrasonic transducer.

Background

The conventional ultrasonic transducers are mostly prepared from rigid piezoelectric materials and rigid electrodes, and the ultrasonic transducers cannot conform to the surface profile of an object to be measured in a curved, irregular or complex shape, so that the consistency of the distance between the ultrasonic transducers and the interface of the object to be measured is poor, and finally, huge acoustic energy reflection and waveform distortion can be caused by air gaps or poor contact generated on the interfaces, so that unreliable results are generated. Therefore, in order to improve the consistency of the distance from the ultrasonic transducer to the outline of the irregular object to be measured, flexible ultrasonic transducers have been developed.

Currently, piezoelectric materials commonly used in flexible ultrasonic transducers are mainly flexible 1-3 type piezoelectric composite materials (1 represents a one-dimensional piezoelectric rod, 3 represents a three-dimensional structure (such as a cuboid structure)) and flexible 0-3 type piezoelectric composite materials (0 represents 0-dimensional particles, 3 represents a three-dimensional structure (such as a cuboid structure)). The flexible 1-3 type piezoelectric composite material is formed by inserting a one-dimensional inorganic piezoelectric rod into a flexible substrate with a three-dimensional structure, but after the composite material is subjected to multiple deformations, the inorganic piezoelectric rod can fall off from the substrate, so that the flexible piezoelectric film is invalid, the service life is short, the flexibility of the composite material can be limited by the inorganic piezoelectric rod, and the flexibility is poor. The flexible 0-3 type piezoelectric composite material is formed by dispersing inorganic piezoelectric particles with zero dimension in a flexible substrate with a three-dimensional structure, although the piezoelectric composite material is good in flexibility and long in service life, generally, in order to ensure the flexibility of the piezoelectric composite material, the inorganic piezoelectric particles are often scattered on the flexible substrate with the three-dimensional structure in a sparse way, so that the inorganic piezoelectric particles are mutually independent and are far apart, and the flexibility is difficult to ensure if the inorganic piezoelectric particles are closely spaced, however, the arrangement mode is that the inorganic piezoelectric particles are all equivalent to being wrapped by thicker insulating polymers, so that when the piezoelectric composite material is polarized, the voltage dispersed on the inorganic piezoelectric particles is small, the piezoelectric particles are difficult to sufficiently polarize, and the problem that the piezoelectric performance of the piezoelectric composite material is poor due to insufficient polarization is caused.

Therefore, the flexible piezoelectric composite material of the 1-3 type or the flexible piezoelectric composite material of the 0-3 type has the problem that the flexible piezoelectric composite material and the flexible piezoelectric composite material are difficult to have excellent flexibility and piezoelectric performance at the same time, so that the prepared ultrasonic transducer has the problems of poor tensile performance and poor piezoelectric performance.

Disclosure of Invention

Based on the above, there is a need to provide a stretchable piezoelectric film and a preparation method thereof, and a stretchable ultrasonic transducer, wherein the stretchable piezoelectric film has the characteristics of excellent stretchability, piezoelectric performance, electromechanical coupling performance and low acoustic impedance, so that the stretchable piezoelectric film can be directly used for the preparation of the ultrasonic transducer, and the prepared ultrasonic transducer has excellent stretchability and piezoelectric performance.

The stretchable piezoelectric film comprises an elastic matrix, a polymer carrier and inorganic piezoelectric phase particles loaded on the polymer carrier, wherein a flexible three-dimensional network structure is formed among the inorganic piezoelectric phase particles through the polymer carrier, and the elastic matrix is flexibly filled in pores of the three-dimensional network structure.

In one embodiment, the material of the polymer carrier is selected from a non-conductive three-dimensional polymer selected from at least one of polydimethylsiloxane, polyvinylidene fluoride, polyvinyl alcohol, and epoxy.

In one embodiment, the elastic matrix is a monolithic structure having three-dimensional voids, and the three-dimensional voids of the elastic matrix interpenetrate with the voids of the flexible three-dimensional network structure.

In one embodiment, the elastomeric matrix is selected from a polydimethylsiloxane matrix, an elastomeric polyurethane matrix, or a thermoplastic polyester elastomer matrix.

In one embodiment, the material of the polymer carrier is selected from non-conductive nanowires selected from at least one of cellulose nanowires, polydimethylsiloxane nanowires, polyvinylidene fluoride nanowires, polyvinyl alcohol nanowires, epoxy nanowires.

In one embodiment, the elastic matrix is selected from natural elastic rubber particles that fill in the pores of the flexible three-dimensional network structure.

In one embodiment, the mass fraction of the elastic matrix in the stretchable piezoelectric film is 35% -55%, the mass fraction of the inorganic piezoelectric phase particles in the stretchable piezoelectric film is 25% -50%, and the mass fraction of the polymer carrier in the stretchable piezoelectric film is 10% -25%;

And/or the inorganic piezoelectric phase particles are at least one selected from lead zirconate titanate particles, lead magnesium niobate-lead titanate particles, lithium niobate particles and lead lanthanum zirconate titanate ceramic particles.

A preparation method of a stretchable piezoelectric film comprises the following steps:

providing an elastic matrix, wherein the elastic matrix has a three-dimensional pore structure;

dispersing a polymer carrier in an organic solvent, and then adding inorganic piezoelectric phase particles to obtain mixed slurry, wherein the mass ratio of the inorganic piezoelectric phase particles to the polymer carrier is more than or equal to 3:1.25;

injecting the mixed slurry into the three-dimensional pore structure of the elastic matrix, and centrifuging to obtain a composite, wherein the centrifuging speed is 2000-4000 rpm, and the centrifuging time is 30-50 min;

and carrying out hot pressing and curing on the composite body to obtain the stretchable piezoelectric film.

providing a suspension of a polymer carrier;

dispersing the elastic matrix in an organic solvent, and then adding inorganic piezoelectric phase particles to obtain a mixed dispersion liquid;

adding the suspension of the polymer carrier and the vulcanization system material into the mixed dispersion, then adding sulfuric acid solution and performing emulsification reaction to obtain a solution containing a reaction product;

And filtering, washing and drying the solution containing the reaction product in sequence, and then carrying out hot pressing and solidification to obtain the stretchable piezoelectric film.

A stretchable ultrasonic transducer comprising a stretchable piezoelectric film as described above and electrodes composited on two opposite surfaces of the stretchable piezoelectric film, each of the electrodes being provided with a tab, wherein the electrodes are stretchable electrodes.

In the invention, the first and inorganic piezoelectric phase particles form a flexible three-dimensional network structure through the polymer carrier, namely the inorganic piezoelectric phase particles and the polymer carrier form a flexible three-dimensional network structure together, so that the inorganic piezoelectric phase particles are distributed in a flexible network form of three-dimensional communication and are closely connected through the polymer carrier, thus when polarization voltage is applied, the voltage can be directly transferred to each inorganic piezoelectric phase particle along the flexible network vein, and the problem of insufficient polarization caused by the fact that the polarization voltage needs to be transferred to each inorganic piezoelectric phase particle through a large amount of polymers is avoided. Therefore, when the stretchable piezoelectric film is polarized, the polarization voltage can directly polarize the inorganic piezoelectric phase particles through the interconnected flexible network structure, so that the stretchable piezoelectric film is sufficiently polarized, and further excellent piezoelectric performance and electromechanical coupling performance are shown.

And secondly, the elastic matrix is filled in pores of a flexible three-dimensional network structure formed by the inorganic piezoelectric phase particles and the polymer carrier, and the network in the flexible three-dimensional network structure is formed by stacking innumerable inorganic piezoelectric phase particles densely, so that a more continuous three-dimensional whole is formed among the inorganic piezoelectric phase particles, the polymer carrier and the elastic matrix, structural collapse of the stretchable piezoelectric film in stretching deformation can be effectively restrained, and the stretchable performance and structural strength of the stretchable piezoelectric film can be further effectively improved.

Thirdly, because of the existence of the polymer carrier and the elastic matrix, the whole stretchable piezoelectric film contains a large amount of polymer, so that the stretchable piezoelectric film has the characteristic of low acoustic impedance.

Therefore, the stretchable piezoelectric film disclosed by the invention has the characteristics of excellent stretchability, piezoelectric performance, electromechanical coupling performance and low acoustic impedance, so that the stretchable piezoelectric film can be directly used for preparing an ultrasonic transducer, and the prepared ultrasonic transducer has excellent stretchability and piezoelectric performance.

Drawings

FIG. 1 is a schematic view showing the microstructure of a stretchable piezoelectric film according to example 1 of the present invention;

FIG. 2 is a schematic view showing the microstructure of a stretchable piezoelectric film according to embodiment 10 of the present invention;

FIG. 3 is a schematic view showing the microstructure of a stretchable piezoelectric film of comparative example 1 of the present invention;

FIG. 4 is a schematic view showing the microstructure of a stretchable piezoelectric film of comparative example 5 of the present invention;

FIG. 5 shows the piezoelectric strain constant retention of the stretchable piezoelectric film of example 1 according to the present invention at different stretching times at a stretching ratio of 260%;

FIG. 6 shows the electromechanical coupling retention of the stretchable piezoelectric film of example 1 of the present invention at different stretching ratios;

FIG. 7 is a graph showing normalized piezoelectric strain constants for the stretchable piezoelectric film of example 1 and the stretchable piezoelectric films of comparative examples 1-5 of the present invention at different stretching ratios;

FIG. 8 is a graph showing the signal amplitude ratio versus peak response retention ratio at different stretching times for the ultrasonic transducer of example 12 of the present invention and the stretchable ultrasonic transducer of comparative example 6 at a stretching ratio of 250%;

FIG. 9 is a graph showing the signal amplitude ratio versus peak response retention ratio at various stretching times for the ultrasonic transducer of example 12 of the present invention and the stretchable ultrasonic transducer of comparative example 7 at a stretching ratio of 250%;

FIG. 10 is a graph showing the signal amplitude ratio versus peak response retention ratio at various stretching times for the ultrasonic transducer of example 12 of the present invention and the stretchable ultrasonic transducer of comparative example 8 at a stretching ratio of 250%;

FIG. 11 is a graph showing the signal amplitude ratio versus peak response retention ratio at various stretching times for the ultrasonic transducer of example 12 of the present invention and the stretchable ultrasonic transducer of comparative example 9 at a stretching ratio of 250%;

fig. 12 is a graph showing the signal amplitude ratio-peak response holding ratio at different stretching times at a stretching ratio of 250% for the ultrasonic transducer of example 12 of the present invention and the stretchable ultrasonic transducer of comparative example 10.

Detailed Description

The stretchable piezoelectric film, the preparation method thereof and the stretchable ultrasonic transducer provided by the invention are further described below.

The invention provides a stretchable piezoelectric film, which comprises an elastic matrix, a polymer carrier and inorganic piezoelectric phase particles loaded on the polymer carrier, wherein flexible three-dimensional network structures are formed among the inorganic piezoelectric phase particles through the polymer carrier, and the elastic matrix is filled in pores of the flexible three-dimensional network structures.

According to the invention, the inorganic piezoelectric phase particles form a flexible three-dimensional network structure through the polymer carrier, namely, the inorganic piezoelectric phase particles and the polymer carrier form a flexible three-dimensional network structure together, so that the inorganic piezoelectric phase particles are distributed in a flexible network structure with three-dimensional communication, and are closely connected through the polymer carrier, so that when polarization voltage is applied, the voltage can be directly transmitted to each inorganic piezoelectric phase particle along the flexible network, and the problem of insufficient polarization caused by the fact that the polarization voltage needs to be transmitted to each inorganic piezoelectric phase particle through a large amount of polymers is avoided. Therefore, compared with the traditional flexible 0-3 type piezoelectric composite material, when the stretchable piezoelectric film is polarized, the polarization voltage can directly polarize the inorganic piezoelectric phase particles through the interconnected flexible network structure, so that the stretchable piezoelectric film is sufficiently polarized, and further excellent piezoelectric performance and electromechanical coupling performance are shown.

Meanwhile, the elastic matrix is filled in the pores of the flexible three-dimensional network structure formed by the inorganic piezoelectric phase particles and the polymer carrier, and the network in the flexible three-dimensional network structure is formed by stacking innumerable inorganic piezoelectric phase particles densely, so that a more continuous flexible three-dimensional whole is formed among the inorganic piezoelectric phase particles, the polymer carrier and the elastic matrix, structural collapse of the stretchable piezoelectric film in stretching deformation can be effectively restrained, and the stretching performance and the structural strength of the stretchable piezoelectric film can be further effectively improved. Therefore, the stretchable piezoelectric film of the present invention has excellent stretchability and structural strength compared to conventional flexible type 1-3 piezoelectric composites.

In addition, the stretchable piezoelectric film integrally contains a large amount of polymer due to the existence of the polymer carrier and the elastic matrix, so that the stretchable piezoelectric film has the characteristic of low acoustic impedance.

In the invention, the component proportions of the elastic matrix, the inorganic piezoelectric phase particles and the polymer carrier in the stretchable piezoelectric film can be adjusted according to the performance requirements. Preferably, the mass fraction of the elastic matrix in the stretchable piezoelectric film is 35% -55%, the mass fraction of the inorganic piezoelectric phase particles in the stretchable piezoelectric film is 25% -50%, and the mass fraction of the polymer carrier in the stretchable piezoelectric film is 10% -25%. By the arrangement, the stretchable performance, the piezoelectric performance, the electromechanical coupling performance and the low acoustic impedance of the stretchable piezoelectric film can be better improved.

In an embodiment, the inorganic piezoelectric phase particles are selected from at least one of lead zirconate titanate (PZT), lead magnesium niobate zirconate titanate (PMN), lead magnesium niobate-lead titanate (PMN-PT), lithium niobate, lead lanthanum zirconate titanate ceramic (PLZT). By this arrangement, the piezoelectric performance of the stretchable piezoelectric film can be further improved.

In the present invention, the form in which the inorganic piezoelectric phase particles are supported on the polymer support is classified into the following two types. The first, the polymer carrier is dispersed in the polymer carrier, and the second, the inorganic piezoelectric phase particles are continuously supported on the surface of the polymer carrier.

In view of the difference in the form of the inorganic piezoelectric phase particles supported on the polymer carrier, the piezoelectric performance in the stretchable piezoelectric film is better improved in order to make the connection between the inorganic piezoelectric phase particles tighter.

In one embodiment, the material of the polymer carrier is preferably selected from a non-conductive three-dimensional polymer, and more preferably, the non-conductive three-dimensional polymer is at least one selected from polydimethylsiloxane, polyvinylidene fluoride, polyvinyl alcohol, and epoxy resin. More preferably, the non-conductive three-dimensional polymer is selected from polydimethylsiloxanes. The arrangement ensures that the inorganic piezoelectric phase particles can be better dispersed in the polymer carrier, and the polymer carrier can be used as a binder, so that the inorganic piezoelectric phase particles are adhered together through the polymer carrier, and the inorganic piezoelectric phase particles can better form a flexible three-dimensional network structure through the polymer carrier, thereby better improving the polarization degree of the stretchable piezoelectric film and further improving the piezoelectric performance of the stretchable piezoelectric film.

In another embodiment, the material of the polymer carrier is selected from the group consisting of non-conductive nanowires, further preferably, the non-conductive nanowires are selected from at least one of cellulose nanowires, polydimethylsiloxane nanowires, polyvinylidene fluoride nanowires, polyvinyl alcohol nanowires, epoxy nanowires. In this way, the inorganic piezoelectric phase particles are continuously supported on the surface of the polymer carrier, and the inorganic piezoelectric phase particles construct a flexible three-dimensional network structure through the polymer carrier.

The method is characterized in that the inorganic piezoelectric phase particles are loaded on the polymer carrier, meanwhile, the elastic matrix can be filled in pores of a flexible three-dimensional network structure formed by the inorganic piezoelectric phase particles and the polymer carrier in different forms, so that the polymer carrier, the inorganic piezoelectric phase particles and the elastic substrate can form a more continuous three-dimensional network structure better, and the stretchability, the electromechanical coupling and the piezoelectricity of the stretchable piezoelectric film are further improved.

In one embodiment, the elastic matrix is a monolithic structure having three-dimensional voids, and the three-dimensional voids of the elastic matrix interpenetrate with the voids of the flexible three-dimensional network structure. The elastic matrix arranged in the way can be better matched with the polymer carrier which is selected from the non-conductive three-dimensional polymer material, so that the inorganic piezoelectric phase particles are better dispersed in the polymer carrier and are bonded together through the polymer carrier, and the inorganic piezoelectric phase particles are more tightly filled in the three-dimensional pores of the elastic matrix, so that the three-dimensional pores of the elastic matrix are mutually inserted with the pores of the flexible three-dimensional network structure which is jointly constructed by the inorganic piezoelectric phase particles and the polymer carrier, a more continuous three-dimensional network structure is formed, the structural collapse of the stretchable piezoelectric film in the stretching deformation can be more effectively restrained, and the stretching performance, the structural strength and the piezoelectric performance of the stretchable piezoelectric film can be further effectively improved.

Preferably, the elastomeric matrix is selected from a Polydimethylsiloxane (PDMS) matrix, an elastomeric polyurethane matrix or a thermoplastic polyester elastomer (TPEE) matrix. By the arrangement, the elastic performance of the elastic matrix can be further improved, and the stretchable performance of the stretchable piezoelectric film can be further improved.

Preferably, the porosity of the elastic matrix is selected from 70% -90%, the pore diameter of the elastic matrix is selected from 20-50 μm, and the through-hole rate of the elastic matrix is selected from 98% -100%. By the arrangement, the elastic effect and the structural strength of the elastic matrix can be further improved, and the stretchability and the structural strength of the stretchable piezoelectric film are further improved, and the elastic service life of the stretchable piezoelectric film is prolonged.

In another embodiment, the elastic matrix fills in pores of the three-dimensional network structure in a plurality of sphere-like structures. Preferably, the elastic matrix is selected from natural elastic rubber particles, and the natural elastic rubber particles are filled in pores of the flexible three-dimensional network structure. The natural elastic rubber particles can be used as elastic microspheres, and the elastic microspheres can be used as repulsive bodies, so that the non-conductive nanowires and the inorganic piezoelectric phase particles are pushed into gaps of the elastic microspheres, the inorganic piezoelectric phase particles can be uniformly attached to a plurality of non-conductive nanowire carriers, and the flexible three-dimensional network structure built by the inorganic piezoelectric phase particles and the polymer carriers is further formed, so that the stretchable piezoelectric film has excellent piezoelectric performance, mechanical performance and stretchability, and has long elastic service life.

Meanwhile, the invention also provides a preparation method of the stretchable piezoelectric film, which comprises the following steps:

s11, providing an elastic matrix, wherein the elastic matrix has a three-dimensional pore structure;

s12, dispersing a polymer carrier in an organic solvent, and then adding inorganic piezoelectric phase particles to obtain mixed slurry, wherein the material of the polymer carrier is at least one of PDMS, PVDF, PVA and epoxy resin;

s13, injecting the mixed slurry into a three-dimensional pore structure of the elastic matrix, and centrifuging to obtain a composite;

s14, carrying out hot pressing and curing on the composite body to obtain the stretchable piezoelectric film.

Preferably, in step S11, the method for preparing the elastic matrix includes the following steps:

s111, providing an elastic polymer solution, wherein the elastic polymer solution is at least one selected from a PDMS solution, an elastic polyurethane solution and a TPEE solution;

s112, filling the elastic polymer solution into pores of foam metal, and curing to obtain a composite structure;

and S113, placing the composite structure in an acid solution to obtain the elastic matrix.

In the invention, foam metal is adopted as a template of a three-dimensional pore structure, namely, a template for preparing an elastic matrix with the three-dimensional pore structure, and in consideration of the structural strength and the elastic effect of the prepared elastic matrix, preferably, in the step S112, the porosity of the foam metal is 70% -90%, the pore diameter of the foam metal is 20 mu m-50 mu m, and the porosity of the foam metal is 98% -100%, so that the elastic matrix prepared later can be ensured to have proper porosity, pore diameter and through-hole rate, and the stretchability and the structural strength of the elastic matrix can be further improved, and the stretchability of the stretchable piezoelectric film can be further improved.

Further preferably, the foam metal is at least one selected from foam nickel, foam aluminum, foam iron, foam titanium, foam zinc, foam iron nickel, foam nickel chromium, foam cobalt nickel and foam stainless steel. More preferably, the metal foam is selected from nickel foam.

In one embodiment, in step S112, the volume ratio of the elastic polymer solution to the metal foam is 70:30.

In one embodiment, in step S113, the composite structure is placed in an acid solution until the foam metal is completely dissolved, and then washed and dried with deionized water, thereby obtaining an elastic matrix having a three-dimensional pore structure. Preferably, the acid solution is selected from dilute sulfuric acid or dilute hydrochloric acid, and more preferably, the acid solution is selected from dilute hydrochloric acid. More preferably, the concentration of the dilute hydrochloric acid is 0.3mol/L to 1mol/L. By the arrangement, the oxidation of the acid solution to the elastic matrix can be avoided, and the foam metal can be fully dissolved to obtain the elastic matrix with a three-dimensional pore structure.

Preferably, in step S12, the mass ratio of the inorganic piezoelectric phase particles to the polymer carrier solution is 3:1.25 or more. The arrangement can enable the inorganic piezoelectric phase particles to be better loaded on the polymer carrier, is favorable for forming a flexible three-dimensional network structure in the elastic matrix through the polymer carrier among the subsequent inorganic piezoelectric phase particles, ensures that the inorganic piezoelectric phase particles forming the flexible three-dimensional network structure are sufficiently polarized, ensures the piezoelectric performance and the electromechanical coupling performance, ensures that the composite piezoelectric film is free from structural collapse and piezoelectric film failure due to the bonding effect of the polymer carrier in the stretching process, and ensures the piezoelectric stability in the stretching process. Further preferably, the mass ratio of the inorganic piezoelectric phase particles to the polymer carrier solution is 3:1. By the arrangement, the inorganic piezoelectric phase particles can be tightly stacked after centrifugation, gaps among the particles are filled with the polymer carrier, and therefore sufficient polarization and stretchability of the stretchable piezoelectric film are more effectively ensured.

In the invention, inorganic piezoelectric phase particles dispersed on a polymer carrier are filled into a three-dimensional pore structure of an elastic matrix by utilizing centrifugal force, and in order to ensure that the inorganic piezoelectric phase particles can be better filled into the three-dimensional pore structure of the elastic matrix, the inorganic piezoelectric phase particles are adhered together through the polymer carrier, so that the polymer carrier and the inorganic piezoelectric phase particles jointly form a flexible three-dimensional network structure. Preferably, in step S13, the centrifugal speed is 2000rpm to 4000rpm, and the centrifugal time is 30min to 50min.

In one embodiment, prior to step S13, further comprising adhering the elastic matrix of step S11 to a glass sheet using a high temperature resistant double sided tape, and then covering the elastic matrix structure using a hollow cylinder having a length of greater than 1 cm. Preferably, the high temperature resistant double-sided tape is a polyimide double-sided tape. The arrangement is convenient for smoothly injecting the mixed slurry in the step S12 into the three-dimensional pore structure of the elastic matrix.

In addition, the invention also provides a preparation method of the stretching piezoelectric film, which comprises the following steps:

s21, providing a suspension of a polymer carrier;

s22, dispersing the elastic matrix in an organic solvent, and then adding inorganic piezoelectric phase particles to obtain a mixed dispersion liquid;

S23, adding the suspension of the polymer carrier and the vulcanization system material into the mixed dispersion, and then adding sulfuric acid solution for emulsification reaction to obtain a solution containing a reaction product;

and S24, filtering, washing and drying the solution containing the reaction product in sequence, and then carrying out hot pressing and solidification to obtain the stretchable piezoelectric film.

In an embodiment, in step S21, the suspension of the polymer carrier is obtained by dispersing the polymer carrier in an organic solvent, and the material of the polymer carrier is selected from nonconductive nanowires, and the nonconductive nanowires are selected from at least one of cellulose nanowires, polydimethylsiloxane nanowires, polyvinylidene fluoride nanowires, polyvinyl alcohol nanowires, and epoxy nanowires.

Preferably, the preparation method of the polymer carrier comprises the following steps:

s211, providing a nano metal oxide template; wherein the thickness of the nano metal oxide template is selected from 30-50 mu m, and the nano pore diameter of the nano metal oxide template is selected from 40-70 nm. Preferably, the nano metal oxide template is selected from a nano aluminum oxide template or a nano zinc oxide template.

S212, dispersing an organic polymer in a solvent to obtain a dispersion liquid; the organic polymer is at least one selected from cellulose, PVDF, polydimethylsiloxane, PVA and epoxy resin, and the solvent can be deionized water.

S213, spin coating the dispersion liquid into the nano holes of the nano metal oxide template, and drying the nano holes in a drying box at 80-100 ℃ for 10-14 h to obtain a composite product.

S214, placing the composite product in an excessive alkaline solution to obtain a mixed solution containing polymer nanowires; wherein the concentration of the alkaline solution is 1mol/L-4mol/L, and the alkaline solution is selected from sodium hydroxide solution or potassium hydroxide solution. The purpose of the device is to dissolve and remove the nano metal oxide template, and the purpose of the excessive alkaline solution is to completely remove the nano metal oxide template and avoid generating metal hydroxide precipitation.

S215, centrifuging the mixed solution containing the polymer nanowires, and then washing and drying to obtain the polymer carrier, wherein the drying temperature is 30-50 ℃.

In one embodiment, in step S22, the elastic matrix is selected from natural elastic rubber particles.

Preferably, in step S23, the reaction temperature is 30 ℃ to 50 ℃, the concentration of the sulfuric acid solution is 0.5mol/L to 1.5mol/L, the vulcanization system material comprises zinc oxide, stearic acid, sulfur, N-cyclohexyl-2-benzothiazole sulfenamide and an emulsifier OP-10, wherein the mass ratio of the zinc oxide, the stearic acid, the sulfur, the N-cyclohexyl-2-benzothiazole sulfenamide, the emulsifier OP-10 and the elastic matrix is 2.9% -3.5%, 1.75% -1.9%, 1.65% -1.75%, 0.85% -0.95% and 0.25% -0.35%, respectively.

In one embodiment, in step S24, the drying temperature is 50 ℃ to 70 ℃, the drying time is 22h to 26h, the hot pressing pressure is 5MPa to 15MPa, the hot pressing and curing temperature is 100 ℃ to 200 ℃, and the hot pressing and curing time is 2min to 10min.

In the preparation method of the stretchable piezoelectric film, inorganic piezoelectric phase particles are continuously loaded on the surface of a polymer carrier and form a flexible three-dimensional network structure together with the polymer carrier, and an elastic matrix after hot press solidification can form a plurality of elastic microspheres similar to spherical structures; meanwhile, through the elastic matrix formed by hot pressing, namely a plurality of spherical elastic microspheres can be repelled, in the process of forming the microspheres, the polymer carrier which is uniformly dispersed in the elastic matrix originally and the two-phase structure of the inorganic piezoelectric phase particles are pushed into gaps among the microspheres, and the inorganic piezoelectric phase particles can be uniformly attached to a plurality of polymer carriers, the flexible three-dimensional network structure formed by the inorganic piezoelectric phase particles and the polymer carriers is further formed, and a more continuous three-dimensional network structure is obtained, so that the stretchable piezoelectric film has excellent mechanical property and stretchability, and has longer elastic service life.

Meanwhile, the flexible three-dimensional network structure formed by the inorganic piezoelectric phase particles and the polymer carrier is crisscrossed and connected with each other among gaps of the elastic matrix (a plurality of elastic microspheres), so that when the stretchable piezoelectric film is polarized, voltage can directly polarize the inorganic piezoelectric phase particles through the network connected with each other, the stretchable piezoelectric film is sufficiently polarized, and further excellent piezoelectric performance and electromechanical coupling performance are shown.

In addition, the elastic base of the stretchable piezoelectric film is an elastic matrix and contains a polymer carrier, so that the stretchable piezoelectric film integrally contains a large amount of polymer, and further has lower acoustic impedance.

In addition, the invention also provides a stretchable ultrasonic transducer, which comprises the stretchable piezoelectric film and electrodes compounded on two opposite surfaces of the stretchable piezoelectric film, wherein each electrode is provided with a tab, and the electrodes are stretchable electrodes.

The stretchable piezoelectric film provided by the invention has the characteristics of excellent stretchability, piezoelectric property, electromechanical coupling property and low acoustic impedance, so that the stretchable piezoelectric film can be directly used for preparing an ultrasonic transducer. Meanwhile, the electrode is a stretchable electrode. Therefore, the stretchable ultrasonic transducer prepared by the stretchable piezoelectric film and the stretchable electrode has excellent stretchable, electromechanical coupling performance and piezoelectric performance, so that the stretchable ultrasonic transducer can be applied to ultrasonic imaging, and can adaptively bend, irregularly or complexly shaped surface contours of an object to be detected, so that the consistency of the distance from the ultrasonic transducer to the interface of the object to be detected is improved, the conditions of acoustic energy reflection, waveform distortion and the like are reduced, and finally, an accurate ultrasonic imaging result with higher quality is obtained.

In addition, the invention also provides a preparation method of the stretchable ultrasonic transducer, which comprises the following steps:

s31, respectively compounding stretchable electrodes on two opposite surfaces of the stretchable piezoelectric film to form a sandwich structure;

s32, applying a direct current electric field to the sandwich structure for polarization, and then respectively leading out the lugs from the stretchable electrodes to obtain the ultrasonic transducer; wherein the electric field strength is 45kV/cm-60kV/cm, the polarization time is 1h-2.5h, and the polarization temperature is 75-90 ℃.

In one embodiment, in step S31, the method for preparing the stretchable electrode includes the following steps:

aqueous solution of polystyrene sulfonate and Na ₂ S ₂ O ₈ 、Fe ₂ (SO ₄ ) ₃ Mixing with deionized water at room temperature in nitrogen atmosphere to obtain mixed solution; wherein 3, 4-ethylene dioxythiophene and Na ₂ S ₂ O ₈ The molar ratio of the 3, 4-ethylenedioxythiophene to the Fe is 1:0.7-1:1 ₂ (SO ₄ ) ₃ The molar ratio of (2) is 1:0.01-1:0.03;

adding an inorganic conductive material and poly (3, 4-ethylenedioxythiophene) into the obtained mixed solution, and stirring and mixing the mixed solution at room temperature in a nitrogen atmosphere to obtain a dark blue poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate solution; wherein the mass ratio of the poly 3, 4-ethylenedioxythiophene to the polystyrene sulfonate is 1:1-1:3;

Dissolving sodium carboxymethyl cellulose in deionized water, uniformly stirring at 30-50 ℃, adding a poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate solution, dimethyl sulfoxide and glycerol, and uniformly stirring at 30-50 ℃ to obtain a composite suspension; wherein the volume ratio of the sodium carboxymethyl cellulose to the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate solution is 1:12-1:14, the volume ratio of the sodium carboxymethyl cellulose to the dimethyl sulfoxide is 1:8-1:10, and the volume ratio of the sodium carboxymethyl cellulose to the glycerol is 1:1-1:3;

and (3) placing the composite suspension in a culture dish, drying at 40-60 ℃, and then stripping from the culture dish to obtain the stretchable electrode.

Preferably, the mass fraction of the inorganic conductive material in the stretchable electrode is 4% -12%. Further preferably, the inorganic conductive material is selected from the group consisting of functionalized carbon nanotubes and MXene (two-dimensional transition metal carbide (nitride)). More preferably, the functionalized carbon nanotubes are selected from carboxylated or hydroxylated carbon nanotubes. The carboxylated or hydroxylated carbon nano tube and the MXene with the multi-active functional group structure can be combined with the hydroxyl structure of the porous cellulose-based polymer through chemical bonds, so that the combination strength between the porous cellulose-based polymer and the composite conductive substance is improved, and the structural strength and the tensile property of the tensile electrode are further improved.

The stretchable electrode prepared by the method is prepared by compounding an inorganic conductive material with carboxymethyl cellulose sodium salt, poly (3, 4-ethylenedioxythiophene) and polystyrene sulfonate. Meanwhile, the inorganic conductive material with the functional group can be used as a conductive reinforcing agent and can form a hydrogen bond with a cellulose structure, so that the overall mechanical property and the conductive property of the stretchable electrode are improved.

Hereinafter, the stretchable piezoelectric film, the method of manufacturing the same, and the stretchable ultrasonic transducer will be further described by the following specific examples.

In the present invention, the piezoelectric performance and the electromechanical coupling performance of the obtained piezoelectric thin film were tested by using a precision piezoelectric tester and an impedance analyzer, and the performance of the ultrasonic transducer was tested by using an ultrasonic pulse transmitter and an oscilloscope.

Preparation examples of stretchable piezoelectric films

Example 1

Filling PDMS solution into pores of foam nickel (with the pore diameter of 30 mu m, the porosity of 80% and the porosity of 98%), curing to obtain a composite structure, placing the obtained composite structure into 0.5mol/L dilute hydrochloric acid until the foam nickel is completely dissolved, and then washing and drying with deionized water to obtain a PDMS matrix with three-dimensional network gaps, namely an elastic matrix with a three-dimensional pore structure, wherein the porosity of the elastic matrix is 80%, the pore diameter of the elastic matrix is 30 mu m, and the porosity of the elastic matrix is selected from 98%.

Sticking the obtained elastic matrix on a glass sheet by using a polyimide high-temperature-resistant double-sided adhesive tape, and covering the elastic matrix by using a hollow cylinder with the length of 1cm as a die; dispersing PZT inorganic piezoelectric phase particles in an epoxy resin solution, and uniformly stirring to obtain mixed slurry, wherein the mass ratio of the PZT inorganic piezoelectric phase particles to the epoxy resin solution is 3:1; pouring the obtained mixed slurry into the obtained elastic matrix structure, and then placing the elastic matrix structure into a centrifugal machine, wherein the rotating speed is 3000rpm, and the centrifugal time is 35min, so that PZT inorganic piezoelectric particles can be fully filled into pores of a three-dimensional network structure of the elastic matrix by utilizing centrifugal force to obtain a composite body; and finally, taking the obtained composite body out of the die and the adhesive tape, and carrying out hot pressing, curing and forming to obtain the stretchable piezoelectric film compounded by the PDMS matrix/PZT/epoxy resin carrier, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 50%, the mass fraction of PDMS matrix in the stretchable piezoelectric film is 35%, and the mass fraction of the epoxy resin carrier in the stretchable piezoelectric film is 15%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 2.6 times the original length of the total length after stretching.

Example 2

The only difference compared with example 1 is that the polymer carrier in example 2 uses PDMS carrier instead of epoxy carrier, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 25%, the mass fraction of PDMS matrix in the stretchable piezoelectric film is 55%, and the mass fraction of PDMS carrier in the stretchable piezoelectric film is 20%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 3.1 times the original length of the total length after stretching.

Example 3

The only difference compared with example 1 is that the polymer carrier in example 3 uses PVDF carrier instead of epoxy resin carrier, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 40%, the mass fraction of PDMS matrix in the stretchable piezoelectric film is 50%, and the mass fraction of PVDF carrier in the stretchable piezoelectric film is 10%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 2.8 times the original length of the total length after stretching.

Example 4

The only difference compared with example 1 is that the polymer carrier in example 4 uses PVA carrier instead of epoxy resin carrier, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 35%, the mass fraction of PDMS matrix in the stretchable piezoelectric film is 40%, and the mass fraction of PVA carrier in the stretchable piezoelectric film is 25%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 2.7 times the original length of the total length after stretching.

Example 5

The only difference compared with example 1 is that the elastic matrix in example 5 employs an elastic polyurethane matrix instead of PDMS matrix, the elastic polyurethane matrix has a porosity of 70%, the elastic polyurethane matrix has a pore size of 20 μm, and the elastic matrix has a through-hole ratio selected from 100%. Wherein, the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 35%, the mass fraction of elastic polyurethane matrix in the stretchable piezoelectric film is 55%, and the mass fraction of PDMS carrier in the stretchable piezoelectric film is 10%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 3 times the total length after stretching.

Example 6

The only difference compared with example 1 is that in the stretchable piezoelectric film in example 6, the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 24%, the mass fraction of PDMS matrix in the stretchable piezoelectric film is 56%, and the mass fraction of epoxy carrier in the stretchable piezoelectric film is 20%.

Example 7

The difference compared with example 1 is only that in the stretchable piezoelectric film in example 7, the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 51%, the mass fraction of PDMS matrix in the stretchable piezoelectric film is 34%, and the mass fraction of epoxy carrier in the stretchable piezoelectric film is 15%.

Example 8

The difference compared with example 1 is only that in the stretchable piezoelectric film in example 8, the porosity of the nickel foam is 90%, the pore diameter of the nickel foam is 50 μm, the pore diameter of the nickel foam is 100%, the porosity of the resulting elastic matrix is 90%, the pore diameter of the elastic matrix is 50 μm, and the pore diameter of the elastic matrix is selected from 100%.

Example 9

The difference from example 1 was only that in the stretchable piezoelectric film in example 9, the porosity of the nickel foam was 70%, the pore diameter of the nickel foam was 20 μm, the porosity of the nickel foam was 98%, the porosity of the elastic matrix was 70%, the pore diameter of the elastic matrix was 20 μm, and the pore diameter of the elastic matrix was selected from 98%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 2.5 times the original length of the total length after stretching.

Example 10

Cleaning a nano aluminum oxide template with the thickness of 40 mu m and the nano aperture of 70nm by using ethanol, acetone and deionized water; PVA is dissolved in a solvent for dispersing NMP, and is stirred uniformly to obtain a dispersion liquid; spin-coating the obtained dispersion liquid into the nano holes of the nano alumina template, placing the nano holes in a drying oven and drying the nano holes at 90 ℃ for 12 hours to obtain a composite product, placing the obtained composite product into a sodium hydroxide solution with the concentration of 2mol/L to obtain a mixed solution containing PVA polymer nanowires, centrifuging and washing the mixed solution containing PVA polymer nanowires, and finally placing the mixed solution into a drying oven at 40 ℃ for drying to obtain the PVA nanowires, namely the polymer carrier.

Dispersing the obtained PVA nanowire powder in N-methyl pyrrolidone to obtain a PVA nanowire suspension; dissolving natural elastic rubber in deionized water to obtain natural elastic rubber mixed solution, wherein the mass fraction of the natural elastic rubber in the natural elastic rubber mixed solution is 55%, and then adding PMN-PT inorganic piezoelectric phase particles into the natural elastic rubber mixed solution to obtain mixed dispersion liquid; adding the suspension of the PVA nanowire and the vulcanizing system material into the obtained mixed dispersion, uniformly stirring at the temperature of 40 ℃, and then adding a sulfuric acid solution with the concentration of 1mol/L to obtain a solution containing a reaction product; wherein the vulcanization system material comprises zinc oxide, stearic acid, sulfur, N-cyclohexyl-2-benzothiazole sulfenamide and an emulsifier OP-10, and the mass ratio of the zinc oxide, the stearic acid, the sulfur, the N-cyclohexyl-2-benzothiazole sulfenamide, the emulsifier OP-10 and the elastic matrix is 3%, 1.8%, 1.68%, 0.9% and 0.25% respectively.

The obtained solution containing the reaction product is sequentially filtered, washed and dried for 24 hours at the drying temperature of 60 ℃, and then hot pressed and cured for 6 minutes at the temperature of 10MPa and 150 ℃ to obtain the stretchable piezoelectric film, wherein the mass fraction of PMN-PT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 30%, the mass fraction of natural elastic rubber matrix in the stretchable piezoelectric film is 55%, and the mass fraction of PVA nanowire carriers in the stretchable piezoelectric film is 15%.

Example 11

In comparison with example 10, only the Polydimethylsiloxane (PDMS) was used instead of PVA in example 11 to prepare a polydimethylsiloxane nanowire carrier.

The elastic stretching limit in the stretchable piezoelectric film obtained in this example is 2.9 times the original length of the total length after stretching.

Comparative example 1

Filling PDMS solution into pores of foam nickel (with the pore diameter of 35 mu m, the porosity of 75% and the porosity of 99%), curing to obtain a composite structure, then placing the obtained composite structure into 0.5mol/L dilute hydrochloric acid until the foam nickel is completely dissolved, and then washing and drying with deionized water to obtain a PDMS matrix with three-dimensional network gaps, namely an elastic matrix with a three-dimensional pore structure, wherein the porosity of the elastic matrix is 75%, the pore diameter of the elastic matrix is 35 mu m, and the porosity of the elastic matrix is 99%.

Sticking the obtained elastic matrix on a glass sheet by using a polyimide high-temperature-resistant double-sided adhesive tape, and covering the elastic matrix by using a hollow cylinder with the length of 1cm as a die; dispersing PZT inorganic piezoelectric phase particles in N-methyl pyrrolidone, and uniformly stirring to obtain mixed slurry, wherein the mass ratio of the PZT inorganic piezoelectric phase particles to a solvent is 3:1.25; pouring the obtained mixed slurry into the obtained elastic matrix structure, and then placing the elastic matrix structure into a centrifugal machine, wherein the rotating speed is 3000rpm, and the centrifugal time is 50min, so that PZT inorganic piezoelectric particles can be fully filled into pores of a three-dimensional network structure of the elastic matrix by utilizing centrifugal force to obtain a composite body; and finally, taking the obtained composite body out of the die and the adhesive tape, and carrying out hot pressing, curing and forming to obtain the stretchable piezoelectric film compounded by the PDMS matrix and the PZT phase, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 45%, and the mass fraction of the PDMS matrix in the stretchable piezoelectric film is 55%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this comparative example is 1.2 times the original length of the total length after stretching.

Comparative example 2

Dispersing PZT inorganic piezoelectric phase particles in an epoxy resin solution, and uniformly stirring to obtain mixed slurry, wherein the mass ratio of the PZT inorganic piezoelectric phase particles to the epoxy resin solution is 3:1; adding the obtained mixed slurry into PDMS solution, stirring uniformly, and placing into a centrifuge with the rotating speed of 3000rpm and the centrifuging time of 50min to obtain a complex; finally, carrying out hot pressing, curing and forming on the obtained composite body to obtain the stretchable piezoelectric film, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 50%, the mass fraction of PDMS in the stretchable piezoelectric film is 35%, and the mass fraction of the epoxy resin carrier in the stretchable piezoelectric film is 15%.

The elastic stretching limit in the stretchable piezoelectric film obtained in this comparative example is 1.3 times the original length of the total length after stretching.

Comparative example 3

Dispersing PZT inorganic piezoelectric phase particles in PDMS solution, stirring uniformly, spin-coating on a glass substrate, hot-pressing, curing and forming to obtain the stretchable piezoelectric film, wherein the mass fraction of PZT inorganic piezoelectric phase particles in the stretchable piezoelectric film is 50%, and the mass fraction of PDMS in the stretchable piezoelectric film is 50%.

The tensile elastic limit of the stretchable piezoelectric film obtained in this comparative example was 2.1 times the total length after stretching, but the piezoelectric strain coefficient thereof was about one fourth of that in the above examples 1 to 11, and the polarization voltage thereof was about 2 to 3 times that in the above examples 1 to 11.

Comparative example 4

A PZT inorganic piezoelectric ceramic sheet with a whole thickness of 200 mu m is adhered to a glass sheet by using a polyimide high-temperature-resistant double-sided adhesive tape, the PZT inorganic piezoelectric ceramic sheet is cut into cuboid PZT rods with side lengths of 60 mu m multiplied by 150 mu m by using a cutting machine, the intervals between the rods are 50 mu m, the PZT ceramic rods are orderly arranged, the bottom surfaces of the PZT ceramic rods are connected with a bottom plate with the thickness of 50 mu m, which is remained after cutting the whole PZT inorganic piezoelectric ceramic sheet, PDMS is filled in the bottom plate, the interval between the rods is filled, the PZT inorganic piezoelectric ceramic sheet is cured at room temperature for 24 hours, and the remaining 50 mu m piezoelectric bottom plate of the whole PZT sheet is cut off, so that the traditional 1-3 stretchable composite piezoelectric film is obtained, wherein the mass fraction of the PZT ceramic rods in the stretchable composite piezoelectric film is 65%, and the mass fraction of the PDMS matrix in the stretchable composite piezoelectric film is 35%.

The elastic stretching limit of the stretchable piezoelectric film obtained by the comparative example is limited by the PZT piezoelectric ceramic rod, the stretching limit is only 1.3 times of the original total length after stretching, and after stretching for 20 times, the PZT piezoelectric ceramic rod and the PDMS elastic substrate are subjected to local separation phenomenon, so that the structure of the stretchable piezoelectric film collapses.

Comparative example 5

And immersing the polyurethane foam board into PZT gel with the concentration of 0.1mol/L, extruding the structure with force to ensure that the PZT gel only wraps a layer on a frame of the polyurethane foam board, then sintering the structure in a high-temperature sintering furnace at 1000 ℃ to ensure that polyurethane is completely volatilized, simultaneously forming an integrated continuous PZT integral frame structure through high-temperature sintering, filling a PDMS substrate, and curing and forming at room temperature for 24 hours.

The elastic stretching limit of the stretchable piezoelectric film obtained by the comparative example is limited by the rigidity of the integrated PZT ceramic frame, the stretching limit is 1.26 times of the original length of the overall length after stretching, and after stretching for 1 time, the integrated PZT frame has a fragmentation phenomenon, so that the PZT frame and the PDMS substrate have a local separation phenomenon, and the structure of the stretchable piezoelectric film collapses.

Stretchable ultrasound transducer preparation examples

Example 12

Sodium polystyrene sulfonate aqueous solution (molecular weight 75000) with the mass fraction of 4% is prepared by mixing, stirring, and concentrating ₂ S ₂ O ₈ 、Fe ₂ (SO ₄ ) ₃ Mixing with deionized water at room temperature under argon atmosphere, stirring for 1 hr to obtain mixed solution, adding hydroxyl or carboxylated carbon nanotube and 3, 4-ethylenedioxythiophene into the mixed solution, and stirring at room temperature under argon atmosphere for 20 hr, wherein 3, 4-ethylenedioxythiophene and Na ₂ S ₂ O ₈ The molar ratio of the 3, 4-ethylenedioxythiophene to the Fe is 1:0.9 ₂ (SO ₄ ) ₃ The molar ratio of the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate is 1:0.02, and finally the dark blue poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate solution is obtained, wherein the mass ratio of the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate is 1:2.

Dissolving sodium carboxymethyl cellulose with molecular weight of 250000 in deionized water, stirring at 40 ℃ until the sodium carboxymethyl cellulose is uniformly dispersed, adding the obtained poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonate solution, dimethyl sulfoxide and glycerol, and stirring at 40 ℃ until the sodium carboxymethyl cellulose is uniformly dispersed to obtain a composite suspension; wherein the volume ratio of the sodium carboxymethyl cellulose to the poly 3, 4-ethylenedioxythiophene-polystyrene sulfonate solution is 1:13, the volume ratio of the sodium carboxymethyl cellulose to the dimethyl sulfoxide is 1:9, the volume ratio of the sodium carboxymethyl cellulose to the glycerol is 1:2, and the mass of the hydroxyl or carboxylated carbon nano tube is 8% of the total mass of the stretchable electrode; pouring the obtained composite suspension into a culture dish, drying at 50 ℃ for 24 hours, and stripping from the culture dish to obtain the stretchable electrode, wherein the elastic stretching limit of the stretchable electrode is 3.23 times of the original length of the stretched electrode.

Respectively compounding the stretchable electrodes obtained in the above on two opposite surfaces of the stretchable piezoelectric film obtained in example 1 to form a sandwich structure; and then, applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 55kV/cm, the polarization time is 1.5h, and the polarization temperature is 80 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the stretchable ultrasonic transducer.

Example 13

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in example 2 to form a sandwich structure; and then, applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 50kV/cm, the polarization time is 2h, the polarization temperature is 85 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the stretchable ultrasonic transducer.

Example 14

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in example 5 to form a sandwich structure; and then, applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 55kV/cm, the polarization time is 2h, and the polarization temperature is 85 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the stretchable ultrasonic transducer.

Example 15

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in example 8 to form a sandwich structure; and then, applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 55kV/cm, the polarization time is 2h, and the polarization temperature is 85 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the stretchable ultrasonic transducer.

Example 16

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in example 10 to form a sandwich structure; and then, applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 55kV/cm, the polarization time is 2h, and the polarization temperature is 85 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the stretchable ultrasonic transducer.

Comparative example 6

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in comparative example 1 to form a sandwich structure; and then applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 1kV/cm, the polarization time is 10h, the polarization temperature is 85 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the ultrasonic transducer.

Comparative example 7

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in comparative example 2 to form a sandwich structure; and then applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 130kV/cm, the polarization time is 1.5h, and the polarization temperature is 80 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the ultrasonic transducer.

Comparative example 8

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in comparative example 3 to form a sandwich structure; and then applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 110kV/cm, the polarization time is 1.5h, and the polarization temperature is 80 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the ultrasonic transducer.

Comparative example 9

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in comparative example 4 to form a sandwich structure; and then applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 55kV/cm, the polarization time is 1.5h, and the polarization temperature is 80 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the ultrasonic transducer.

Comparative example 10

The stretchable electrodes obtained in example 12 were respectively laminated on two opposite surfaces of the stretchable piezoelectric film obtained in comparative example 5 to form a sandwich structure; and then applying a direct current electric field to polarize the obtained sandwich structure (wherein the electric field strength is 55kV/cm, the polarization time is 1.5h, and the polarization temperature is 80 ℃), and then respectively leading out the electrode lugs from the stretchable electrode to obtain the ultrasonic transducer.

Referring to fig. 1 to 2, fig. 1 is a schematic view of the microstructure of a stretchable piezoelectric film of example 1, wherein 1 represents a PDMS substrate, 2 represents an epoxy carrier, and 3 represents PZT inorganic piezoelectric phase particles. As shown in FIG. 1, PZT inorganic piezoelectric phase particles are closely connected to form a three-dimensional network, gaps among the PZT inorganic piezoelectric phase particles are filled with an epoxy resin carrier, and gaps of a three-dimensional network structure are filled with a PDMS matrix, namely the three-dimensional network is of a flexible structure. Fig. 2 is a schematic view of the microstructure of the stretchable piezoelectric film of example 10, wherein 4 represents natural elastic rubber particles (elastic matrix), 5 represents PVA nanowire carriers, 6 represents PMN-PT inorganic piezoelectric phase particles, and the PMN-PT inorganic piezoelectric phase particles are supported on PVA nanowires (polymer carriers) as shown in fig. 2, and the PVA nanowires are used as carriers of the PMN-PT inorganic piezoelectric phase particles, and the PVA nanowire/PMN-PT inorganic piezoelectric phase particle structures together form a three-dimensional network structure, and gaps of the three-dimensional network structure are filled with the natural elastic rubber particles, i.e., the three-dimensional network itself is a flexible structure.

Referring to fig. 3 and 4, fig. 3 is a schematic view of the microstructure of the stretchable piezoelectric film of comparative example 1, wherein 7 represents a PDMS substrate, 8 represents an air gap, and 9 represents PZT inorganic piezoelectric particles. As shown in fig. 3, the internal structure of the stretchable piezoelectric film of comparative example 1 is a three-dimensional network structure, the inorganic piezoelectric phase particles are closely connected to form a three-dimensional network, but the inorganic piezoelectric phase particles are filled with air, and when the composite film is polarized, the air has air inside, and the breakdown voltage of the air is about 3kV/cm, so that the high-voltage breakdown of the air is avoided, the applied polarization voltage is lower, the polarization effect is poor, and the three-dimensional network itself is a flexible structure, but a large amount of air gaps are filled among the particles forming the network. Fig. 4 is a schematic view of the microstructure of the stretchable piezoelectric film of comparative example 5, in which 10 represents a PDMS substrate and 11 represents a PZT ceramic frame. As shown in fig. 4, the stretchable piezoelectric film of comparative example 5 has a three-dimensional network structure inside, but the network structure is formed by a monolithic PZT ceramic frame, which is an integral unit, and corresponds to a porous PZT ceramic frame in a block shape, but the pore size and porosity of the PZT ceramic frame are large, and the frame itself is still a rigid structure.

From these results, it is clear that the stretchable piezoelectric film obtained in comparative example 1 and comparative example 5 has problems of poor piezoelectric properties, poor flexibility, and poor stretchability, and it is difficult to satisfy both excellent stretchability and piezoelectric properties, and the stretchable piezoelectric film of the present invention can have excellent stretchability, piezoelectric properties, and electromechanical coupling properties.

To better illustrate that the stretchable piezoelectric film of the present invention has excellent stretchability, piezoelectric properties, and electromechanical coupling coefficient, the applicant conducted the tensile properties, electromechanical coupling coefficients, and piezoelectric properties tests on the piezoelectric film of example 1, and the test results are shown in fig. 5 and 6. As can be clearly seen from fig. 5, the tensile piezoelectric film in example 1 of the present invention has almost unchanged retention rate of the piezoelectric strain constant under different stretching times, and is proved to have excellent tensile properties, i.e. the original piezoelectric strain constant can be maintained after a plurality of stretching cycles. As is clear from fig. 6, the tensile piezoelectric film in example 1 of the present invention has substantially unchanged electromechanical coupling retention after being stretched at different stretching ratios, which proves that the tensile piezoelectric film has excellent tensile properties, i.e. the original electromechanical coupling coefficient can be maintained at different stretching ratios.

The stretching ratio in the present invention is (total length after stretching/original length) multiplied by 100%, wherein the total length after stretching is (stretched length+original length); the elongation is (stretched length/original length) times 100%.

In addition, in order to compare the tensile properties and piezoelectric properties of the stretchable piezoelectric films of the present invention and the stretchable piezoelectric films of the comparative examples, the applicant provided normalized piezoelectric strain constants (normalized piezoelectric strain coefficients refer to the ratio of the piezoelectric strain coefficient of each example, each comparative example to the piezoelectric strain coefficient of comparative example 3) of the stretchable piezoelectric films of the example 1 and the comparative examples 1 to 5 at different tensile ratios, and specifically please refer to fig. 7, in which A, B, C, D, E, F represents example 1, comparative example 2, comparative example 3, comparative example 4 and comparative example 5, respectively. As shown in fig. 7, the conventional type 1-3 stretchable piezoelectric film of comparative example 4 has a slightly higher piezoelectric strain coefficient than that of example 1 of the present invention, but has a limited stretching ratio, i.e., a maximum stretching ratio of 130%, and a larger stretching ratio causes a partial separation of the rigid piezoelectric rod from the elastic polymer substrate, thereby causing a sharp decrease in the piezoelectric strain coefficient with an increase in the stretching ratio. In comparison, the stretchable piezoelectric film of example 1 of the present application has higher stretching performance due to the flexible network structure and the elastic polymer substrate inside, and also retains higher piezoelectric performance, and the decrease of piezoelectric strain coefficient does not occur when the stretching ratio is less than 260%. While comparative example 3 is a conventional 0-3 type stretchable piezoelectric film, it is known from the test structure that the same excellent stretching property is obtained, but the piezoelectric strain coefficient is lower than that of example 1 of the present application due to the difficulty in polarizing sufficiently.

The piezoelectric strain constant of comparative example 5 is higher than that of comparative examples 1 to 3, but the tensile properties are similar to those of comparative examples 1 to 3, and the maximum tensile ratio is 126%, because the internal PZT frame is a rigid structure, and thus the internal rigid PZT frame structure is broken during the stretching, and gaps are left between the broken portions and the elastic polymer substrate without filling any polymer, and the piezoelectric properties and the electromechanical coupling properties are greatly impaired after stretching several times, like those of comparative examples 1 and 4, i.e., the tensile properties and the piezoelectric properties cannot be ensured at the same time as the stretchable piezoelectric film. In contrast to comparative example 5, the inorganic piezoelectric phase particles and the polymer carrier adopted in example 1 of the present invention together form a flexible three-dimensional active piezoelectric network, which ensures the tensile properties and the piezoelectric properties, and the conclusion can be visually observed from fig. 5 and 6.

Comparative example 1 is a composite of a network structure composed of purely inorganic piezoelectric phase particles and an elastic substrate, but because of the lack of a polymer carrier, air gaps exist between the network structure and the elastic polymer substrate, and the breakdown voltage of air is lower and is generally lower than 3kV/cm, so that the polarization voltage of comparative example 1 can only be very low (less than 3 kV/cm), the composite piezoelectric film is difficult to polarize, and piezoelectric performance is hardly shown. Meanwhile, in comparative example 2, a piezoelectric film formed by compounding inorganic piezoelectric phase particles with epoxy resin and PDMS is adopted, but the inside of the piezoelectric film is not constructed into a three-dimensional network structure, so that the required polarization voltage is very high, and the piezoelectric film is difficult to sufficiently polarize, so that the piezoelectric film has low piezoelectric performance.

In summary, the stretchable piezoelectric film of the present invention has both higher piezoelectric performance and excellent stretching performance compared to other comparative examples due to the flexible three-dimensional active piezoelectric network.

The stretchable ultrasonic transducer prepared in example 12 and the ultrasonic transducers obtained in comparative examples 6 to 10 were subjected to a stretching number test at a stretching ratio of 250%, and changes in the morphology and performance of the ultrasonic transducers were detected, as shown in fig. 8 to 12, wherein G, H, J, K, M, N represents example 12, comparative example 6, comparative example 7, comparative example 8, comparative example 9 and comparative example 10, respectively. As shown in fig. 8 to 9 and 11 to 12, the ultrasonic transducers of comparative examples 6, 7, 9 and 10, after having undergone a stretching deformation at a stretching ratio of 250%, had collapsed in structure and had a reduced quality, and in particular, the piezoelectric thin films of comparative examples 6, 7, 9 and 10 had a lower stretchability, and therefore had broken at one stretching at a stretching ratio of 250%, and had a reduced sensitivity as a cliff. The ultrasonic transducer has unchanged structure and good quality. Meanwhile, as is clear from fig. 8, the sensitivity of the ultrasonic transducer in comparative example 6 is almost 0 because the stretchable piezoelectric film has low piezoelectric performance due to the limitation of polarization voltage, and thus the process of converting the electrical signal and the acoustic signal into each other by the ultrasonic transducer is almost impossible. As can be seen from fig. 10, the stretchable ultrasonic transducer of comparative example 8 has a higher sensitivity retention during the stretching cycle, but from the test on the stretchable piezoelectric film shown in fig. 7, since the piezoelectric performance of the stretchable piezoelectric film used for the ultrasonic transducer is far lower than that of the stretchable film used in example 12, the stretchable ultrasonic transducer of comparative example 8 has a sensitivity far lower than that of the stretchable ultrasonic transducer of example 12 of the present invention, although the sensitivity retention is higher.

Therefore, the ultrasonic transducer prepared from the stretchable piezoelectric film and the stretchable electrode has excellent stretching performance, piezoelectric performance and stability.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. The stretchable piezoelectric film is characterized by comprising an elastic matrix, a polymer carrier and inorganic piezoelectric phase particles loaded on the polymer carrier, wherein a flexible three-dimensional network structure is formed among the inorganic piezoelectric phase particles through the polymer carrier, and the elastic matrix is filled in pores of the flexible three-dimensional network structure;

The material of the polymer carrier is selected from a non-conductive three-dimensional polymer, the non-conductive three-dimensional polymer is selected from at least one of polydimethylsiloxane, polyvinylidene fluoride, polyvinyl alcohol and epoxy resin, the elastic matrix is of a monolithic structure with three-dimensional pores, the three-dimensional pores of the elastic matrix are interpenetrated with the pores of the flexible three-dimensional network structure, the elastic matrix is selected from a polydimethylsiloxane matrix, an elastic polyurethane matrix or a thermoplastic polyester elastomer matrix, and the inorganic piezoelectric phase particles are selected from at least one of lead zirconate titanate particles, magnesium niobate lead titanate particles, lithium niobate particles and lead lanthanum zirconate titanate ceramic particles;

the mass fraction of the elastic matrix in the stretchable piezoelectric film is 35% -55%, the mass fraction of the inorganic piezoelectric phase particles in the stretchable piezoelectric film is 25% -50%, and the mass fraction of the polymer carrier in the stretchable piezoelectric film is 10% -25%.

2. The stretchable piezoelectric film is characterized by comprising an elastic matrix, a polymer carrier and inorganic piezoelectric phase particles loaded on the polymer carrier, wherein a flexible three-dimensional network structure is formed among the inorganic piezoelectric phase particles through the polymer carrier, and the elastic matrix is filled in pores of the flexible three-dimensional network structure;

The material of the polymer carrier is selected from nonconductive nanowires, the nonconductive nanowires are selected from at least one of cellulose nanowires, polydimethylsiloxane nanowires, polyvinylidene fluoride nanowires, polyvinyl alcohol nanowires and epoxy resin nanowires, the elastic matrix is selected from natural elastic rubber particles, the natural elastic rubber particles are filled in pores of the flexible three-dimensional network structure, and the inorganic piezoelectric phase particles are selected from at least one of lead zirconate titanate particles, magnesium niobate lead zirconate titanate particles, lead magnesium niobate-lead titanate particles, lithium niobate particles and lead lanthanum zirconate titanate ceramic particles;

3. A method for preparing a stretchable piezoelectric film, comprising the steps of:

providing an elastic matrix having a three-dimensional pore structure, the elastic matrix being selected from the group consisting of a polydimethylsiloxane matrix, an elastic polyurethane matrix, or a thermoplastic polyester elastomer matrix;

Dispersing a polymer carrier in an organic solvent, and then adding inorganic piezoelectric phase particles to obtain mixed slurry, wherein the mass ratio of the inorganic piezoelectric phase particles to the polymer carrier is more than or equal to 3:1.25, and the material of the polymer carrier is at least one selected from PDMS, PVDF, PVA and epoxy resin;

4. A method for preparing a stretchable piezoelectric film, comprising the steps of:

providing a suspension of a polymer carrier, wherein the material of the polymer carrier is selected from a non-conductive nanowire, and the non-conductive nanowire is at least one of a cellulose nanowire, a polydimethylsiloxane nanowire, a polyvinylidene fluoride nanowire, a polyvinyl alcohol nanowire and an epoxy resin nanowire;

dispersing an elastic matrix in an organic solvent, and then adding inorganic piezoelectric phase particles to obtain a mixed dispersion liquid, wherein the elastic matrix is selected from natural elastic rubber particles;

5. A stretchable ultrasound transducer comprising a stretchable piezoelectric film according to any one of claims 1 to 2 and electrodes composited on two opposite surfaces of the stretchable piezoelectric film, each of the electrodes being provided with a tab, wherein the electrodes are stretchable electrodes.