乙二醇和丙三醇二元系玻璃化转变和协同松弛

Glass transition and cooperative relaxation of ethylene glycol and glycerol binary mixtures

为了估算乙二醇(EG)在慢速降温下的玻璃化转变和协同松弛参数,利用差示扫描量热法(DSC)测量了连续升降温条件下(10K.min-1)乙二醇和丙三醇二元系(EG/G)在玻璃化转变温度Tg前后的表观比热容.利用曲线拟合方法得到了EG/G基于Adam-Gibbs(AG)模型的协同松弛参数.结果表明,随组分的变化,玻璃化转变温度Tg、玻璃化转变过程中的比热跃迁ΔCp(Tg)、AG模型参数、松弛时间和动力学脆度等均呈规律性变化,据此可外推得到EG的玻璃化转变和AG模型参数.松弛时间和动力学脆度的分析结果表明,EG的动力学脆度比丙三醇的小,二元系动力学脆度的分析结果可以和Tg,ΔCp(Tg),松弛时间分布参数和协同重排域等的分析结果相互印证,从而证明了AG模型作为现象学模型描述EG/G结构松弛的有效性.但在解析EG/G协同重排域的微观参数时,AG理论遇到困难.

In order to estimate the glass transition and cooperative relaxation parameters of ethylene glycol （EG） at slow cooling rate, differential scanning calorimetry （DSC） were employed to obtain the apparent specific heat capacities of EG and glycerol Binary mixtures near the glass transition temperatures （Tg）. The same cooling and heating rate （10 K · min^-1） was used for all the samples. Nonlinear Adam-Gibbs （AG） relaxation time expression was used to model the calorimetric data and curve-fitting method was used to obtain the AG parameters. The results indicated that Tg, specific heat capacity increment at Tg, △Cp（Tg）, AG model parameters, relaxation time and dynamic fragility changed regularly with the variation of the composition of binary mixtures. This makes it possible to estimate the parameters of pure EG by short linear extrapolation. The calculation of relaxation time and dynamic fragility （m） indicated that EG is somewhat ＂stronger＂ than glycerol and this is consistent with Tg, △Cp （Tg） and non-exponential parameter analysis. The results confirmed that AG model can be used as a valid expression for phenomenological description of EG/G binary mixtures. But this model can not produce physically reasonable micro-parameters of cooperative rearranging regions （CRRs） in AG sense.