Accurate Measurements of Nonlinear Dielectric Relaxation Spectra of Polymers

我们研制了一种能精确测量非线性介电弛豫谱的仪器。在样品上施加一个具有最小畸变的正弦电场，并通过数字傅里叶变换对基频和高次谐波的介电位移进行定向。在0.01Hz-10kHz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。利用该装置，我们研究了三种聚合物；聚偏二氰共聚物、聚醋酸乙烯酯和离子导电聚合物。偏乙烯氰共聚物，特别是与醋酸乙烯的共聚物，由于具有非常大的线性介电常数，近年来引起了人们的兴趣。非线性电偶测量表明，第三阶非线性介电常数与频率的关系为：ε - 3^*= δ ε - 3/ (1+i ω - tau_3) ^3，符合现象学预测。结合DELTA epsilon_1和DELTA epsilon_3的知识，可以估计出更多的等效偶极子的数量和矩。偏二甲基氰化物聚合物的大介电常数归因于非常大的等效偶极矩，这表明它们的分子运动中存在很强的协同性。由于电致伸缩的作用，聚醋酸乙烯酯表现出变形的非线性光谱。对弹性柔度的额外测量允许减去这一贡献，从而得到与乙烯基氰化物共聚物观察到的一致的本征非线性光谱。类似的测量已经扩展到离子导电聚合物，包括聚乙烯氧化物及其衍生物。结果立即转换为非线性导电光谱，以便讨论这种聚合物的传导机制。在这些结果的基础上，我们已经证实，非线性介电光谱与线性对应物相结合，提供了聚合物体系中分子相互作用和动力学的有用信息。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