Accurate Measurements of Nonlinear Dielectric Relaxation Spectra of Polymers

我们研制了一种精确测量非线性介电弛豫谱的装置。在样品上施加一个畸变最小的正弦电场，用数字傅里叶变换检测基波和高次谐波介质位移。在0.01Hz-10 kHz范围内，我们得到了线性和第三非线性介电常数作为频率的函数。使用该装置，我们研究了三种聚合物：偏二氰乙烯共聚物，聚乙酸乙烯酯和离子导电聚合物。乙烯叉氰共聚物，特别是与醋酸乙烯酯的共聚物，由于其非常大的线性介电常数，在过去几年中引起了人们的兴趣。非线性双折射测量表明，第三种非线性介电常数取决于频率，根据唯象预测，ε_3 ^*= Δ ε_3/（1+i ω τ_3）^3。关于Δ ε_1和Δ ε_3的组合知识允许估计 关于我们 等效偶极子的数量和力矩。偏二氰乙烯基聚合物的大的结晶度归因于其很大的等效偶极矩，表明其分子运动存在很强的协同效应.聚醋酸乙烯酯显示出变形的非线性光谱由于电致伸缩的贡献。弹性柔量的额外测量允许减去此贡献以产生与对偏二氰乙烯共聚物观察到的那些一致的固有非线性光谱。类似的测量已经扩展到离子导电聚合物，包括聚环氧乙烷及其衍生物。结果立即转换成非线性导电光谱，使讨论的导电机制，这些聚合物的基础上，我们已经证实，非线性介电谱结合其线性对应提供有用的信息，分子间的相互作用和动力学的聚合物系统。少

We have developed an apparatus for making accurate measurements of non-linear dielectric relaxation spectra. A sinusoidal electric field with minimal distorsion is applied to a sample and fundamental and higher harmonic dielectric displacements are ditected by means of digital Fourier transform. We obtained linear and third non-linear permittivities as a function of frequency in a 0.01Hz-10kHz range. Using this apparatus, we investigated three kinds of polymers ; vinylidene cyanide copolymers, polyvinyl acetate, and ion-conducting polymers.1. Vinylidene cyanide copolymers, especially with vinyl acetate, have attracted interest past few years because of their very large linear permittivity. Nonlinear didelctric measurements have shown that the third nonlinear permittivity depends upon frequency according to, epsilon_3^*=DELTA epsilon_3/ (1+i omega tau_3) ^3 in accordance with phenomenological prediction. Combined knowledge about DELTA epsilon_1 and DELTA epsilon_3 allow estimates of the … More number and moment of equivalent dipoles. The large permittivities of vinylidene cyanide opolymers are attributed to very large equivalent dipole moments suggesting an existence of strong cooperativity in their molecular motions.2. Polyvinyl acetate is shown to exhibit deformed nonlinear spectra due to the contribution of electrostriction. Additional measurements of the elastic compliance allow subtraction of this contribution to yield the intrinsic nonlinear spectra which are consistent with those observed for vinylidene cyanide coplymers.3. Analogous measurements have been extended to ion-conducting polymers including polyethylene oxide and its derivatives. The results are immediately converted into non-linear conductive spectra to enable discussion on conduction mechanisms of such polymers.On the basis of these results, we have confirmed that the non-linear dielectric spectroscopy in combination with its linear counterpart provides useful information about molecular interaction and dynamics in polymeric systems. Less