| The electroactive polymer polyvinylidene-trifluoride(P(VDF-TrFE))has become a research hotspot in the fields of ultrasonic,sensor and transducer due to its excellent dielectric,ferroelectric,piezoelectric and pyroelectric properties.However,P(VDF-TrFE)is a kind of semicrystalline polymer,and the temperature conditions during the crystallization process have great influence on its crystallization properties and condensed state structure,which will affect the electrical properties of the material.In view of this,this paper aims to study the relationship between P(VDF-TrFE)film forming conditions and its dielectric,ferroelectric and piezoelectric properties.Firstly,molecular dynamics simulation is used to calculate the crystallinity of P(VDFTrFE),and the difference of crystallinity of P(VDF-TrFE)with different VDF content is quantitatively compared by calculating characterization parameters.Subsequently,P(VDF-TrFE)films were prepared by the traditional solution ducting method at different annealing temperatures.The relationship between the crystallization and electrical properties of the films was investigated experimentally.Finally,the molecular chain modeling and MD simulation of P(VDF-TrFE)were carried out by molecular dynamics simulation.Through analyzing the simulation results,the influence mechanism of the crystalline structure of the polymer on the electrical properties was clarified.The main content of this paper is as follows.1)The solution extension method is adopted.P(VDF-TrFE)80/20 mol%,P(VDFTrFE)75/25 mol%,P(VDF-TrFE)60/40 mol%and P(VDF-TrFE)65/35 were prepared at 140℃,200℃,room temperature and annealing temperature in ice water XRD,DSC and FTIR were used to characterize the crystal properties and phase structure of mol%thin films.The results show that the crystallization properties of P(VDF-TrFE)films at 140℃ are better than other conditions,and P(VDF-TrFE)80/20 mol%and P(VDF-TrFE)75/25 mol%have higher crystallinity at 140℃.By comparing the XRD peaks of the four components of P(VDF-TrFE)films,it is found that with the decrease of the molar content of VDF,the Angle of the diffraction peak tends to shift to the lower Angle.In addition,it is found that P(VDF-TrFE)60/40 mol%is the all-trans phase and 3/1-helical phase,while the other three components are the all-trans structure,which lays a foundation for the analysis of electrical properties.2)The dielectric spectrum and temperature spectrum of different P(VDF-TrFE)samples were systematically tested.It is found that after annealing at 140℃,the permittivity(εr)of P(VDF-TrFE)75/25 mol%at low frequency(100 Hz)is 13 and the loss(tanδ)is 0.02,the sr of P(VDFTrFE)65/35 mol%is 17.2 and the tanδ is 0.03.Good dielectric property;At high frequency(10 MHz),the εr of P(VDF-TrFE)75/25 mol%reaches 10.9,the tanδ increases to 0.15,the εr of P(VDF-Trfe)65/35 mol%reaches 13.6,the tanδ increases to 0.19,showing obvious relaxation phenomenon.The tanδ of P(VDF-TrFE)decreased with the increase of VDF content.The peak dielectric temperatures of P(VDF-TrFE)65/35mol%and 60/40 mol%with low VDF molar content were found to move towards high temperature with the increase of test frequency,and the peak positions were consistent with the DSC test results,indicating that these two P(VDFTrFE)were typical relaxation ferroelectrics.When the content of VDF is high(75 mol%and 80 mol%),the dielectric temperature peak ratio of P(VDF-TrFE)films after annealing at 140℃ is higher than that of the samples with low VDF components,indicating that these two samples are typical intrinsic ferroelectrics.3)The piezoelectric strain constant(d33),saturation polarization value(PS)and residual polarization value(Pr)of P(VDF-TrFE)polymer were investigated.It is found that the d33 of all samples increases with the increase of the polarization electric field intensity,and the higher d33 can be obtained by 150 MV·m-1 polarization electric field.At this time,the piezoelectric constant of 80/20 mol%of P(VDF-TrFE)reaches the maximum value of-25 pC·N-1.The ferroelectric properties of the films with different components were characterized by hysteresis loops.The results show that the hysteresis curves of four different components of P(VDF-TrFE)all show the characteristics of typical ferroelectrics,and when the content of VDF is 75 mol%,the amplitude of Ps and Pr increases with the increase of annealing temperature.4)XRD,mean azimuth-shift,non-bond energy and crystallinity of P(VDF-TrFE)with different molar ratios(80/20 mol%,75/25 mol%,60/40 mol%and 65/35 mol%)were simulated by molecular dynamics and compared with the experimental results.The results show that with the increase of molar mass of TrFE.The diffraction peak positions(2θ)of P(VDF-TrFE)80/20mol%,75/25 mol%,65/35 mol%and 60/40 mol%are 20.26°,20.14°,19.9° and 19.84°,respectively,which are consistent with XRD results.The results of mean azimuthal shift showed that the molecular chain motion shift was larger during annealing at 140℃,which was more conducive to the formation of TTTT conformation.The calculation of non-bond energy shows that the molecular decline rate is the fastest in the range of 0～50 ps,and the molecular energy gradually becomes stable after 50～350 ps,indicating that P(VDF-TrFE)has good stability.Molecular dynamics simulation results show that the crystallinity of P(VDF-TrFE)80/20 mol%and P(VDF-TrFE)75/25 mol%at 140℃ are 92.06%and 90.78%,respectively.In this paper,the crystallization,phase structure,dielectric,ferroelectric and piezoelectric properties of P(VDF-TrFE)films with different VDF molar content were studied by molecular dynamics simulation and experimental tests,which can lay a foundation for the preparation of subsequent devices. |
PDF Full Text Request