聚偏氟乙烯薄膜压电性的研究

本文研究了聚偏氟乙烯的压电性。聚偏氟乙烯薄膜是用DMA溶剂浇铸而成,然后进行单轴拉伸,并采用热驻极的方法使薄膜成极。实验结果表明,压电活性依赖于拉伸比、极化电场、极化温度和极化时间。此外,还研究了聚偏氟乙烯压电薄膜的稳定性和某些使用特性。     

Piezoelectricity and pyroelectricity of polyvinylidene fluoride corona-poled at elevated temperature

X-ray diffraction, thermally stimulated depolarization, and piezoelectric and pyroelectric current measurements have been carried out on biaxially oriented polyvinylidene fluoride film, corona-poled both negatively and positively, at elevated temperature. Larger piezoelectric and pyroelectric coefficients are obtained at lower values of the poling field, when corona charging takes place at elevated temperature rather than room temperature. Negative charging is more effective than positive. The polarization mechanism is dipole alignment, and a conversion of Form-II crystallites to Form I. The large space-charge injected by the corona, and trapped in the material, acts through creation of high internal fields, and shows little, if any, piezoelectric and pyroelectric effects of its own.     

Piezoelectricity and viscoelastic crystalline dispersion in highly oriented poly(vinylidene fluoride)

The effects of poling temperature on piezoelectricity and its thermal stability were investigated on the basis of the thermal molecular motion associated with the crystalline region. This was done by using a film of highly oriented poly(vinylidene fluoride) containing form-I crystals. The film was prepared by a zone-drawing apparatus of the forced-quenching type. The piezoelectric stress constant e₃₁ is a monotonically increasing function of the poling temperature which becomes steeper above ca. 320 K and again at ca. 400 K. The degree of orientation of the crystal b axis generated by poling also increases more steeply with poling temperature above ca. 320 K and again at 400 K. These temperatures correspond, respectively, to the crystalline dispersion temperature at 11 Hz, designated as α_c, and the initiation temperature T_pm of large-scale molecular motion corresponding to premelting of form-I crystals. Thus the effect of poling temperature on piezoelectricity closely reflects the moleculer motion in form-I crystals. The annealing temperature T'_a at which e₃₁ decreases to 70% of that of unannealed sample by annealing a poled sample increases with the poling temperature and again this increase is steeper above poling temperatures of ca. 320 K and ca. 400 K. Thus the decay of piezoelectricity depends on both the α_c temperature and T_pm.     

Broadband dielectric characterization of piezoelectric poly(vinylidene fluoride)thin films between 278 K and 308 K

This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers.     

Poling-time dependence of the field-induced phase transition and piezoelectric response of poly(vinylidene fluoride) films

We have examined the poling time dependence of the field-induced phase transition (from phase II to polar phase II) of biaxially oriented poly(vinylidene fluoride) films by x-ray methods. These results were compared with the poling-time dependence of the piezoelectric response (d₃₁ and e₃₁) determined using a piezotron Model U (Toyo Seiki, Tokyo). The piezoelectric response shows an initial rapid increase with poling time followed by a slow increase as the poling time increases. The x-ray results show that the field-induced phase transition is time dependent, and occurs first for those crystallites with their a axes perpendicular to the film surface. Crystallites with a in the plane of the film transform at a much slower rate. The data indicate that the poling time dependence of d₃₁ and e₃₁ (and, presumably, film polarization) are dependent on the transition rates.     

Piezoelectricity in uniaxially stretched and plasticized nylon 11 films

The combined effect of uniaxial stretching and plasticization of nylon 11 films on the resulting piezoelectric response was studied. Three different kinds of samples were studied for nylon 11 α′-form films: (1) uniaxially stretched at 150°C, (2) samples uniaxially stretched at 150°C and then plasticized by immersion in 2-ethyl 1,3-hexanediol, and (3) samples plasticized and then uniaxially stretched. The largest piezoelectric response was obtained from the samples which were plasticized prior to uniaxial stretching under identical poling conditions. For the case of nylon 11 δ′-form films, two different kinds of experiments were performed: (1) samples uniaxially stretched at room temperature were subsequently plasticized by immersion in the plasticizer and a comparison of their piezoelectric response made with that of the unplasticized samples as a function of poling field; (2) the plasticizer content dependence of the piezoelectric response from these samples was studied. In both cases, d₃₁ was observed to be higher for the plasticized films compared with the unplasticized films. The piezoelectric stress constant e₃₁ showed a small decrease with plasticization. X-ray diffraction studies indicated a small conversion of δ′-phase to α′-phase with plasticization. No significant changes were observed in the x-ray diffraction scans taken before and after poling.     

Importance of the metal–polymer interface for the piezoelectricity of polyvinylidene fluoride

The piezoelectric effect in films of polyvinylidene fluoride (PVF₂) is investigated using optical and ultrasonic detection techniques. From the analysis of the vibrational resonance frequencies of a freely suspended film we conclude that the polarization induced in PVF₂ is inhomogeneous across the volume of the sample. Poling the foils in a sandwich configuration or using blocking electrodes, we can clearly demonstrate that the piezoelectric effect in PVF₂ originates from the positive metal electrode. Monitoring the time dependence of the piezoelectric effect during the poling process, a fast and slow component are observed. Using a blocking electrode, however, the same dynamical poling behavior is found only if the contacting metal electrode is positive. In view of these observations, which clearly demonstrate the importance of the metal–polymer interface for the strong piezoelectricity of PVF₂, the existing theoretical models, based on the bulk properties of the polymer, are critically reviewed.     

Ferroelectric and piezoelectric properties of a quenched poly(vinylidene fluoride-trifluoroethylene) copolymer

The ferroelectric and piezoelectric properties of melt-quenched unoriented poly(vinylidene fluoride-trifluoroethylene) (73 : 27) copolymer films as a function of the number of poling cycles have been studied. The investigation revealed that quenched films exhibit a decrease in D-E hysteresis behavior as the number of poling cycles increases when the samples are poled at room temperature. Corresponding decreases in remanent polarization, Pr, as well as small increases in the coercive field, Ec, were observed as the material was subjected to successive poling cycles. The piezoelectric coefficients, d₃₁ and e₃₁, also decreased as the number of poling cycles increased. In addition, a clear reduction in the “apparent” Curie transition temperature between unpoled and poled material was observed. Preliminary evidence indicates that films quenched from the melt to below T_c do not form a stable ferroelectric crystal phase as previously believed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2671–2679, 1997     

偏氟乙烯-四氟乙烯共聚物热释电性的研究

本实验室合成了一系列不同组成的偏氟乙烯-四氟乙烯共聚物(F_(24)),并通过浇铸与极化制成了热电薄膜. 实验结果表明F_(24)薄膜的热释电系数依赖于极化温度,极化电场,极化时间。选用适当的极化条件可以提高薄膜的热释电性。热释电系数还与共聚物组成有关,当共聚物中,偏氟乙烯的克分子百分数为80～85时,热释电系数最高.此外,还测定了F_(24)的电滞回线。     

Piezoelectric and pyroelectric properties of new polysiloxane smectic C elastomers

We investigated the pyroelectric and piezoelectric effects of new smectic C^* liquid crystalline elastomers. The materials are made up of a flexible polysiloxane backbone bearing chiral mesogenic side groups and are cross-linked via alkylene chains. The polar structure of the mesophase is evidenced by the observation of piezoelectric and pyroelectric effects. Integration of the pyroelectric coefficient over the whole smectic C^* stability range allows the determination of the spontaneous polarization (P_S = 3–6 nC/cm²). Due to the rubber elasticity, these materials exhibit a high piezoelectric response. The piezosignal at room temperature does not vanish after annealing at temperatures even much higher than the Curie point. The piezoelectric coefficient d₃₁ ranges from 0.5 pC/N for non-poled samples to 2.5 pC/N after application of a poling field.     

含苯并噻唑偶氮发色侧基的两种非线性光学高分子

含苯并噻唑偶氮发色侧基的两种非线性光学高分子刘志红，过俊石，谢洪泉（华中理工大学化学系武汉４３００７４）关键词苯并噻唑，聚氨酯，聚丙烯酸酯，非线性光学聚合物用于集成光学光波导电光调制器件的非线性光学聚合物要求具有大的电光系数、高透明性、良好的加工性能...     

Piezoelectric PVDF-TrFE nanocomposite mats filled with BaTiO3 nanofibers: The effect of poling conditions

BaTiO₃ nanofibers (BT NFs), prepared by electrospinning, were used as a filler for electrospun poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) nanocomposite mats. The phase structure and the effect of poling conditions on the piezoelectric properties of PVDF-TrFE/BT nanocomposites were investigated. The results showed an improved degree of crystallinity (78.6%) and a high β-crystal phase (up to 98.3%) in all electrospun samples, independent of the nanofiber content. The two-step poling method, applying electric fields of opposite polarity, led to significantly improved piezoelectric constants d₃₃ (−31.7 pC N⁻¹), strongly dependent on the added BaTiO₃ nanofibers. The inclusion of piezoelectric ceramic nanofibers into a polymer matrix, easily carried out by means of electrospinning, followed by an ad hoc optimized poling treatment, allowed to develop flexible materials with enhanced piezoelectric properties, potentially exploitable in innovative conversion systems used in wearable and sensing devices.     

Ferroelectric behavior and polarization mechanism in odd‐odd polyamide 11,11

Ferroelectric and piezoelectric behavior in odd‐odd polyamide 11,11 are successfully detected for the first time. The maximum coercive field (E_c) of 90 MV/m, and a remnant polarization (P_r) of 40 mC/m² are obtained at room temperature. A piezoelectric strain coefficient (d₃₃) value as high as ?3.9 pC/N has been found in stretched polyamide 11,11 film. The structural change of samples before and after poling is investigated by wide‐angle X‐ray diffraction patterns, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The results indicate that the nature of the ferroelectricity originates from amide group dipoles in the γ‐form crystal regions. Hysteresis behavior appears to result from the crystallites reversal mechanism. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1094–1099     

Thermally stable nonlinear optical polyurea functionalized by multiple charge‐transfer chromophore

A novel high glass‐transition temperature (272 °C) polyurea functionalized by a multiple charge‐transfer chromophore, 2‐{4‐[4,5‐bis(4‐nitrophenyl)imidazolyl]phenyl}‐4,5‐bis(4‐aminophenyl)imidazole, was synthesized. Simultaneous poling and polymerization and the in situ second‐harmonic generation (SHG) measurement technique was carried out to evaluate the thermal stability of the poling‐induced orientation. The nonlinear optical coefficient d₃₃ of poled polyurea film was 24 pm/V at 1064 nm fundamental wavelength. The SHG signal of the poled polymer film was quite stable below 200 °C and still remained 80% of its initial value after heating at 250 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4297–4301, 2002     

SYNTHESIS OF A NOVEL SELF-ASSEMBLING NLO POLYMERIC FILM*

By covalently binding chromophore NPP, N-(4-nitrophenyl)-(L)-prolinol, to a structurallycontrolled cage-like cross-linking polymer (SCCP), a modified nonlinear optical (NLO) polymeric filmprepared by "in situ poling and sol-gel" process successfully overcame the fundamental problem of NPPchromophores subliming out from the cages of the "doped" NLO polymeric film when heated or placed underUV light. Its d_(33) (coefficient of second harmonic generation) is 2.0×10~(-8) esu. measured by IR dichroism. Themodified film has a low decay of the SHG signal and preserves 94% of the initial value after 50 days at roomtemperature. These properties match that of the "doped" film, indicating that the modified film also retainsthe main advantages of the "doped" film.     

In situ poling and orientation stability of chromophore-bearing ladderlike polysiloxanes

A new, specially designed nonlinear optical (NLO) polymer is composed of ladderlike polysilsesquioxane as a backbone and “side-on or end-on” fixed stilbene chromophores. In-situ poling was carried out simultaneously during film formation via solvent evaporation and crosslinking which was caused by sequential hydrolysis and condensation of remained Si-H groups on macromolecules. The dipolar orientation after poling is described by an order parameter Φ which was measured using an original linear optical technique–UV dichroism. Orientation order and its decay are influenced by chromophore loading, crosslinking degree and poling condition. Compared with corresponding single chain polymers, a poled thin film of ladderlike NLO polymers demonstrates more stable poling-induced orientation.     

Harnessing Plasticity in an Amine-Borane as a Piezoelectric and Pyroelectric Flexible Film

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d₃₃≈10–16 pC N⁻¹, and pyroelectric coefficient of p≈25.8 μC m⁻² K⁻¹ were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of 6.3.     

Harnessing Plasticity in an Amine‐Borane as a Piezoelectric and Pyroelectric Flexible Film

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d₃₃≈10–16 pC N^?1, and pyroelectric coefficient of p≈25.8 μC m^?2 K^?1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of 6.3.     

异氰酸酯交联的环氧树脂基二阶非线性光学聚合物

通过双酚A 二 (缩水甘油醚 )与苯胺的逐步聚合反应合成环氧树脂类先驱聚合物BPAN ,进一步通过先驱聚合物的后重氮偶合反应 ,制备了侧链带偶氮生色团的二阶非线性光学聚合物BPAN 1A NT .将BPAN 1A NT与适当量的异氰酸酯交联剂M2 0S混合 ,得到了双组分非线性光学聚合物体系BPAN 1A NT M2 0S .该体系在电场极化的同时可发生交联固化 ,极化后其二阶非线性光学系数高达 10 5 2pm v(λ =1 0 6 4 μm) ,同时还具有很好的极化偶极取向稳定性 ,2 0 0℃时的非线性光学系数仍可维持在初始的 80 %以上 .上述双组分非线性光学聚合物材料 (BPAN 1A NT M2 0S)同时具有高二阶非线性光学系数和高极化偶极取向稳定温度 ,可以预期 ,在聚合物电光调制器、光开关等器件中将有很好的应用前景 .     

Aging of piezoelectricity in poly(vinylidene fluoride)

This report describes isothermal aging of piezoelectricity in poly(vinylidene fluoride) (PVDF) based on long-term heat treatments between 40 and 160°C. The results demonstrate that no piezoelectric decay occurs below about 60°C, that between 60 and 160°C the aging behavior follows logarithmic kinetics, and that aging is linearly dependent on temperature. Both uniaxial and biaxial PVDF show similar trends, but piezoelectric decay is more rapid for uniaxial film. Decay of permanent poling-induced polarization is identified as the likeliest cause of piezoelectric aging, and piezoelectric decay is found to be associated with long-range annealing effects which also produce macroscopic shrinkage of the PVDF film.