丙三醇浓溶液Tg附近协同松弛的量热研究

利用差示扫描量热法测量了丙三醇水溶液Tg前后的比热容. 通过曲线拟合获得AGF模型参数. 研究结果表明, 该模型很好地预测了(Tg+20 K)以下体系的结构松弛时间. 协同重排活化能(Δμ')和协同重排域尺寸(z*)的分析结果表明, 只有选择比聚合物大得多的某一协同重排位形数, 用AGF方法得到的z*才具有物理意义. 作为材料常数的Δμ' 随体系水含量的增加而逐渐降低. 用Donth方法得到的丙三醇水溶液的协同重排域长度尺度(ξCRR)随着水含量的增加逐渐降低, 且其变化趋势可与Δμ'的分析结果相符. 但用AGF方法和Donth方法得到的协同重排域尺寸不能统一.

Calorimetric Studies on Cooperative Relaxation Near Tg for a Series of Glycerol Aqueous Solutions with High Concentrations

In order to examine the validity of entropically based nonlinear Adam-Gibbs equation(AGF) on the describing of cooperative relaxation of H-bond molecular liquid, differential scanning calorimetry(DSC) was employed to obtain the specific heat capacities of glycerol aqueous solutions in the temperature range of 118—218 K. Curve fitting technology was used to obtain the AGF model parameters. The results indicate that AGF formula can be used to predict the relaxation time below (Tg+20 K). The temperature-invariant activation energies(Δμ') and the sizes of cooperatively rearranging region(z*) were analyzed via AGF model and Johari's method. Physically reasonable z* can only be obtained when larger values of configuration numbers(W*) were chosen. The values of Δμ' decreased with increasing water content in the glass. The length scales of the cooperative rearranging region(ξCRR) were also estimated from the temperature fluctuation theory proposed by Donth. It was found that the ξCRR decreased from 3.01 to 2.06 nm when the fraction of glycerol decreased from 1 to 0.6 in the solutions. The values of z* obtained by using Johari's methods is 3.47 for glycerol, which is significantly less than the number of molecules estimated by Donth' method(583) in the CRR.