不同结晶度的乙二醇及其水溶液玻璃化转变与焓松弛

为了考察晶体成分对无定形成分玻璃化转变和结构松弛行为的影响,利用差示扫描量热法(DSC),结合低温显微技术,研究了乙二醇(EG)及其50％水溶液在不同结晶度时的玻璃化转变和焓松弛行为.采用等温结晶方法控制骤冷的部分结晶玻璃体中的晶体份额.DSC结果表明,对于部分结晶的EG,只有单一的玻璃化转变过程,而对于50％EG,当结晶度不同时,不同程度地表现出两次玻璃化转变（无定形相Ⅰ和无定形相Ⅱ）.相Ⅰ的玻璃化转变温度和完全无定形态的含水EG的玻璃化转变温度相一致;相Ⅱ的玻璃化转变温度要比此温度约高6 ℃.低温显微观察结果印证了DSC实验结果.DSC等温退火的实验和KWW(Kohlrausch-Williams-Watts)衰变函数分析结果表明,EG无定形和50％EG中的两种无定形有不同的焓松弛行为.

Glass Transition and Enthalpy Relaxation Behavior of Ethylene Glycol and Its Aqueous Solution with Different Crystallinity

In order to investigate the effects of the crystals on glass transition and enthalpy relaxation behaviors, differential scanning calorimetry (DSC) and cryomicroscopy technique were used to study ethylene glycol (EG) and its aqueous solution (50％EG, mass fraction) with different crystallinity. Isothermal crystallization method was used in devitrification region to get different crystal fractions after samples quenched below the glass transition temperature (Tg).The DSC thermograms upon heating showed that EG had a single glass transition while 50％EG had two (amorphous phaseⅠ and the warmer one, phase Ⅱ)with different crystal fractions. Tg of phaseⅠ was equal to while phase Ⅱ was 6 ℃ higher than Tg of 50％EG in purely amorphous phase. It is believed that the lower transition represents the glass transition of bulk amorphous phase of EG aqueous solution glass state, while the second one is related to inclusions, whose mobility is restricted by ice crystals. Cryomicroscopy experiments indicated that EG crystal had regular shape while ice crystal in 50％EG aqueous solution glass matrix had no clear surface. It can be concluded that contact area between crystal and amorphous phase in EG is larger than that in 50％EG, which is helpful to explain double glass-like transitions. Isothermal annealing experiments at temperatures lower than Tg were also conducted on these amorphous samples in DSC, and KWW（Kohlrausch-Williams-Watts）decay function was used to analyze DSC enthalpy relaxation data. The results showed that both the two amorphous phases presented in 50％EG experience enthalpy relaxation, and the relaxation process of phase Ⅰ is faster than that of phase Ⅱ at the same value of (Tg－Ta).