用DSC研究1,2-丙二醇及其水溶液的协同松弛行为

DSC Study on the Cooperative Relaxation Behaviors in 1,2-Propanediol and Its Aqueous Solutions

为了验证基于位形熵的非线性Adam-Gibbs协同松弛模型(AGV)能否用于描述小分子氢键液体的协同松弛行为,利用差示扫描量热法(DSC)测量了连续升降温条件下1,2-丙二醇及其四种水溶液在115～230K之间的比热容,利用曲线拟合技术获得AGV模型参数.结果表明,AGV模型可以重现体系的实验比热容数据.1,2-丙二醇表现出与其水溶液明显不同的松弛行为,但水含量的变化对松弛行为的影响并不明显.利用AGV方法和Johari方法分别对协同重排活化能(△μ')和协同重排域(CRR)尺寸(z*)作了分析.只有选择比聚合物大得多的某一协同重排位形数,以AGV方法得到的z*才不至于没有物理意义.Johari方法的分析结果表明,Tg温度下1,2-丙二醇的CRR内有约3个分子,但对应的协同重排位形数(W*)却较聚合物高出很多.Donth的基于热力学温度波动理论的分析表明,1,2-丙二醇及其水溶液的CRR尺寸随组分的变化趋势可与△μ'和非指数参数的分析结果相吻合,但得到的1,2-丙二醇的CRR内有约350个分子,从而和Johari的分析结果产生巨大差别.

In order to examine the validity of entropically based nonlinear Adam-Gibbs equation （AGV） on the describing of cooperative relaxation of H-bond molecular liquid, differential scanning calorimetry （DSC） was employed to obtain the specific heat capacities （Cp） of 1,2-propanediol （PD） and its aqueous solutions in the range of 115-230 K. Curve fitting technology was used to obtain the AGV model parameters. The resuits indicated that AGV formula can be used to reproduce the experimental normalized Cp curves of present systems. Different relaxation behaviors were found between PD and its aqueous solutions, but the water content shows neglectable effect on the relaxation behaviors in aqueous solutions. The activation energies （△μ′） and the sizes of cooperatively rearranging region （Z^＊） were analyzed using AGV model and Johari＇s thermodynamic method. Physically reasonable Z^＊ numbers （W^＊） were chosen. For pure compound, can only be obtained when larger values of configuration Johari＇s method yielded 3 PD molecules in the cooperatively rearranging region （CRR）, but the values of W^＊ seems to be anomalistically higher than those of polymers. The length scales of CRR （ξCRR） were also estimated from the temperature fluctuation theory proposed by Donth. With the variation of the composition, ξCRR obtained using Donth＇s method was consistent with the △μ′ and non-exponential parameter analysis. But the number of molecules included in the CRR was 350 for PD, which seemed to be no possibility to reconcile it with the Z^＊ in AG sense.