1,2-丙二醇水溶液玻璃化转变与结构松弛

为了考察水含量对1, 2-丙二醇水溶液玻璃化转变和结构松弛参数的影响, 用差示扫描量热法(DSC), 测量了5种高浓度1, 2-丙二醇水溶液(60%、70%、80%、90%、100%, w)玻璃化转变区域的表观比热容. 用5种降温速率(1、2、5、10、20 K·min-1)和10 K·min-1的升温速率获得玻璃化转变的相关参数. 玻璃化转变温度分析结果表明, 虽然水含量增加能从总体上降低体系的玻璃化转变温度, 但与纯羟基类多元醇相比, 水对1, 2-丙二醇的增塑作用并不显著. 结构松弛活化能计算结果表明, 体系水含量的增加能明显降低结构松弛活化能. 脆度分析结果表明, 随着体系水含量增加, 动力学脆度逐渐降低, 但热力学脆度是先升高后降低, 在80%左右达到最大值. 结构松弛协同重排域计算结果表明, 当浓度由60%增加至100%时, 玻璃化转变特征长度由2.79 nm增加至3.57 nm.

Glass Transition and Structure Relaxation of 1, 2-Propanediol Aqueous Solutions

In order to examine the effects of water contents on glass transition and structure relaxation parameters of 1, 2-propanediol (PD) aqueous glasses, apparent specific heat capacity during glass transition processes of five PD aqueous solutions with high concentrations (60%, 70%, 80%, 90%, and 100%, w) were determined using the differential scanning calorimetry (DSC). Five cooling rates (1, 2, 5, 10, 20 K·min-1) and one heating rate (10 K·min-1) were used to obtain the glass transition and structure relaxation parameters. Water seemed to be no obvious plasticization effect on 1, 2-propanediol (compared to some “pure hydroxyl group” linear polyalcohol) since the glass transition temperatures of the aqueous solutions were only slightly decreased with the increasing of water content. The structure relaxation activation energies were found to decrease as the water content increased. A comparison of thermodynamic fragility(ΔCp) and dynamic fragility (Angell′s fragility) was present and no similar trend was found with the changing of the component, since the former increased first and decreased last. The calculating results of dynamic fragility indicated that 1, 2-propanediol aqueous solutions behaved as though they were “stronger” than the pure solute. The sizes of cooperative rearrangement region (CRR) discussed in the term of glass transition characteristic length were determined using Donth’s thermodynamic temperature fluctuant method. It was found that the sizes of CRR decreased as the water content increasing in 1,2-propanediol aqueous solutions.