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

通过介电弛豫分析食品成分分散体系的内部结构。

基本信息

批准号：
11660120
负责人：
KUMAGAI Hitoshi
金额：
$ 2.3万
依托单位：
THE UNIVERSITY OF TOKYO
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

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.

介电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 '通常减小，并且介电损耗ε"由于偶极矩的延迟而显示出峰值，这种现象被称为介电弛豫。本文用介电弛豫法分析了明胶的玻璃化转变，在-20℃ ~ 60℃的温度范围内，测量了明胶在100 ~ 1 MHz频率范围内的介电性质。通过改变明胶溶液的干燥时间制备了不同含水量的样品，用DSC测定了玻璃化转变温度T_g，观察到玻璃态明胶的介电弛豫最大值ε”，由ε"峰计算弛豫时间τ。由<ax>τ的Arrhenius图求得的介电弛豫活化能E_随含水量的增加而减小。根据E_的数量级，认为所观察到的介电弛豫是反映分子局部运动的β弛豫。τ和E是表征水对玻璃态材料增塑作用的合适参数。另一方面，在低频和温度T_g附近或以上，含电解质和/或水的材料的电性能，由于大的直流电导率，ε“峰被掩盖了。为了分析这样的系统，ε“和ε“被转换成M^* 形式（M^*=1/（ε '-iε”）= M'+ iM”，i，虚部单位）M”的峰值，例如，观察到弛豫现象，并由M”峰计算弛豫时间τ_N。活化能E_τ由1/τ_N的Arrhenius图求得。玻璃态的E_τ值大于橡胶态。