Microdetermination of sulfite with a piezoelectric crystal detector

A piezoelectric method is proposed for the determination of sulfite in concentration range 1 × 10^–7–1 × 10^–5 mol/1. The method is based on the redox reaction of sulfite with iodine followed by measuring frequency change of the piezoelectric crystal caused by the unreacted iodine. The method is applied to the determination of sulfite in liquor.     

Synthesis and Characterization of PZT Fibers via Sol-Gel

A fiber forming PZT gel containing 58.5 wt% PZT was synthesized by using zirconium-n-propylate, titanium-iso-propylate, lead acetate and butoxyethanol. Unseeded PZT gels and gels containing 0.5 wt% PZT perovskite seeds (Ø = 200–300 nm) could be extruded through a monofilament nozzle (Ø = 100 m) at pressures between 50 and 150 bar, whereas PZT gels, containing 1 and 2 wt% PZT particles, were pressed through the nozzle at higher pressures (200–300 bar). The microstructure of unseeded and seeded (0.5, 1, 2 wt% PZT) PZT fibers was characterized by SEM. Unseeded fibers had three different shells at 450°C: an external dense shell (approx. 200 nm thick), a middle shell consisting of a porous structure (1.5m thick) and the center of the fiber, characterized by a matrix containing globular particles. At 700°C, a 200–250 nm thick and dense external shell and a porous fiber interior were be observed. 2 wt% of PZT seeds was necessary to densify the fiber completely. The seeds were located in the center of each PZT perovskite rosette.     

Dependence of dielectric,ferroelectric, and piezoelectric properties on crystalline properties of p(VDF‐co‐TrFE) copolymers

Thermal processing at various temperatures has been used to fabricate poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐co‐TrFE)] films with varied crystalline properties in an attempt to improve their piezoelectric properties. Although the dielectric constant of the films annealed at higher temperature is smaller than that of cooled and quenched ones, it has been shown that the annealed films possess larger crystallinity and stacked lamellar crystal grain size. The ferroelectric domains deriving from crystal region in all the samples are effectively improved by hot polarization. As a result, the remnant polarizations (P_r) and coercive electric field (E_c) of the corresponding films are improved at a low frequency due to the response of dipoles in crystal phase, and the largest piezoelectric constant in the longitudinal thickness mode (d₃₃=?25 pC/N) is obtained in an annealed copolymer film. The results illustrate improving the crystal structure of P(VDF‐co‐TrFE) is an effective way to realize high electromechanical properties, which provides broadly applied scenery for this kind of copolymer in piezoelectric components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

A Selective Pharmaceutical Analysis Technique with Sensitive Piezoelectric Crystal Quartz Sensors

Abstract

The frequency shift of a piezoelectric crystal sensor showed a linear dependence on the concentration for drugs which can be hydrolyzed in base aqueous solutions, at a given reacting time after the addition of the base, when the base concentration is basically constant during the entire measurement period. The sensitivity of the analysis method was improved, if crystal responses at different reacting times were recorded and utilized to estimate component concentration, when used for determining atropine sulfate in a pharmaceutical compound. The analytical results indicated that the selective and sensitive analytical procedure could be easily applied in true low concentration pharmaceutical analysis.     

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.     

Electro-Mechanochemical Atom Transfer Radical Cyclizations using Piezoelectric BaTiO3

The formation and regeneration of active Cu^I species is a fundamental mechanistic step in copper-catalyzed atom transfer radical cyclizations (ATRC). Typically, the presence of the catalytically active Cu^I species in the reaction mixture is secured by using high Cu^I catalyst loadings or the addition of complementary reducing agents. In this study it is demonstrated how the piezoelectric properties of barium titanate (BaTiO₃) can be harnessed by mechanical ball milling to induce electrical polarization in the strained piezomaterial. This strategy enables the conversion of mechanical energy into electrical energy, leading to the reduction of a Cu^II precatalyst into the active Cu^I species in copper-catalyzed mechanochemical solvent-free ATRC reactions.     

高β相聚偏氟乙烯基复合体系的制备及压电性能

为了提高聚偏氟乙烯(PVDF)的压电性能,需要寻找有效的途径来提高PVDF的电活性相(β相)含量。 通过水热法成功合成了Ag、ZnO以及二者复合(Ag-ZnO)的3种类型纳米粒子,并与PVDF共混形成PVDF复合薄膜。 通过表征PVDF复合材料的形貌,结晶性能和压电性能,可以发现Ag-ZnO复合纳米粒子的协同作用可以有效提高PVDF的结晶性能和压电性能。 此外,通过单轴拉伸可以使得所有PVDF膜的β相含量得到进一步提高,其中拉伸后的PVDF/Ag-ZnO纳米颗粒(P-C)的β相物质的量分数最高,达到70.0％,最佳的压电系数(d₃₃)达到了31.0 pC/N。     

Nonlinear thickness-shear vibration of an infinite piezoelectric plate with flexoelectricity based on the method of multiple scales

This paper presents a nonlinear thickness-shear vibration model for onedimensional infinite piezoelectric plate with flexoelectricity and geometric nonlinearity. The constitutive equations with flexoelectricity and governing equations are derived from the Gibbs energy density function and variational principle. The displacement adopted here is assumed to be antisymmetric through the thickness due to the thickness-shear vibration mode. Only the shear strain gradient through the thickness is considered in the present model. With geometric nonlinearity, the governing equations are converted into differential equations as the function of time by the Galerkin method. The method of multiple scales is employed to obtain the solution to the nonlinear governing equation with first order approximation. Numerical results show that the nonlinear thickness-shear vibration of piezoelectric plate is size dependent, and the flexoelectric effect has significant influence on the nonlinear thickness-shear vibration frequencies of micro-size thin plates. The geometric nonlinearity also affects the thickness-shear vibration frequencies greatly. The results show that flexoelectricity and geometric nonlinearity cannot be ignored in design of accurate high-frequency piezoelectric devices.     

Study on wave dispersion characteristics of piezoelectric sandwich nanoplates considering surface effects

In this study, the wave propagation properties of piezoelectric sandwich nanoplates deposited on an orthotropic viscoelastic foundation are analyzed by considering the surface effects (SEs). The nanoplates are composed of a composite layer reinforced by graphene and two piezoelectric surface layers. Utilizing the modified Halpin-Tsai model, the material parameters of composite layers are obtained. The displacement field is determined by the sinusoidal shear deformation theory (SSDT). The Euler-Lagrange equation is derived by employing Hamilton’s principle and the constitutive equations of piezoelectric layers considering the SEs. Subsequently, the nonlocal strain gradient theory (NSGT) is used to obtain the equations of motion. Next, the effects of scale parameters, graphene distribution, orthotropic viscoelastic foundation, and SEs on the propagation behavior are numerically examined. The results reveal that the wave frequency is a periodic function of the orthotropic angle. Furthermore, the wave frequency increases with the increase in the SEs.

     

High diffusion barrier and piezoelectric nanocomposites based on polyvinylidene fluoride‐trifluoroethylene copolymer and hydrophobized clay

Nanocomposites based on polyvinylidene fluoride–trifluoroethylene copolymer and up to 4 vol % of hydrophobized clay nanoparticles are investigated. The structure, piezoelectric properties, and oxygen permeability of solvent cast films are analyzed before and after annealing above the Curie temperature of the polymer. Exfoliation of the clay takes place at concentrations up to 1 vol %, beyond which it rapidly drops and is absent at a concentration of 4 vol %. The presence of clay does not change the crystallinity of the polymer, but leads to a threefold decrease of the oxygen permeability at a concentration of 0.5 vol %. Annealing at 130 °C increases the crystallinity, the proportion of β phase up to 94%, and the piezoelectric coefficient by 20–40% at clay fractions below 1 vol %. Annealing also leads to a remarkable 3‐ to 10‐fold decrease of O₂ permeability and to intriguing changes of the activation energy for O₂ transport, which decreases from 56 kJ/mol for the as‐cast polymer to below 10 kJ/mol for the polymer and exfoliated composite. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1828–1836