Analysis of Inner Structure of Food-Component Dispersed System by Dielectric Relaxation.

介电光谱被广泛用于研究分散体系中的分子动力学。随着频率的增加，介电常数ε‘经常减小，介电损耗ε“由于偶极矩的延迟而出现一个峰值，这就是所谓的介电松弛现象。用介电弛豫法分析了明胶的玻璃化转变过程，在-20℃~60℃的温度范围内，测量了明胶在100 Hz~1 MHz范围内玻璃态的介电性能。通过改变明胶溶液的干燥时间制备了不同含水率的样品，用DSC测定了玻璃化转变温度T_g。ε“的最大值，即玻璃明胶的介电松弛；松弛时间τ由ε”的峰值来估算。由τ的Arrhenius图得到的活化能E&lt；ax&gt；随水含量的增加而减小，介电松弛被认为是反映分子局部运动的β松弛。τ和E被认为是表征水对玻璃材料塑化效应的合适参数。另一方面，在低频和T_g附近或更高的温度下，含有电解液和/或水的材料的电性能，由于较大的直流电导率，ε“峰被遮蔽了。为了分析这类系统，ε“和ε”被转化为M^*形式(M^*=1/(ε‘-Iε“)=M’+Im”，I，虚单位)M“的峰，例如，观察到松弛，并由M”的峰计算松弛时间τ_N。活化能E_τ由1/τ_N的阿累尼乌斯曲线求出。玻璃态的E_τ值大于橡胶态。

Dielectric spectroscopy is widely used to study molecular dynamics in dispersed systems. With increasing frequency, the dielectric constant, ε', often decreases, and the dielectric loss, ε", shows a peak due to the delay in dipole moments, this phenomenon being the so-called dielectric relaxation. In this study, the glass transition of gelatin was analyzed by dielectric relaxation.The dielectric properties of gelatin in the glassy state were measured from 100Hz to 1MHz over a temperature range of -20℃〜60℃. Samples with different water content were prepared by varying the drying time for gelatin solution ; the glass transition temperature, T_g, was determined by DSC.The maximum of ε" , i.e. the dielectric relaxation was observed for glassy gelatin ; the relaxation time τwas evaluated from the peak of ε". The activation energy E_<ax>obtained from an Arrhenius plot of τdecreased with increasing water content Based on the order of magnitude of E, the dielectric relaxation observed was considered be β relaxation reflecting the local motion of molecules. τand E, are considered to be suitable parameters for the characterization of the plasticizing effect of water on a glassy materialOn the other hand, in the low frequencies and at temperatures around or above T_g, the electrical properties of materials containing electrolytes and/or water, the peak of ε"was masked due to large dc conductivity. For analyzing such systems, ε"and ε"were transformed into M^* formalism (M^*=1/(ε'-iε") =M'+iM", i, the imaginary unit) the peak of M", e.g., the relaxation was observed and the relaxation time, τ_N was evaluated from the peak of M". The value of the activation energy, E_τ was evaluated from an Arrhenius plot of 1/τ_N, . The value of E_τ in the glassy state was larger than that in the rubbery state.