Acta Phys. -Chim. Sin. ›› 2004, Vol. 20 ›› Issue (07): 701-706.doi: 10.3866/PKU.WHXB20040707

• ARTICLE • Previous Articles     Next Articles

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

Gao Cai;Wang Wen-Hua;Hu Tong-Ji;Xu Yi;Zhou Guo-Yan;Hua Ze-Zhao   

  1. Institute of Cryomedicine and food refrigeration, Shanghai University for Science and Technology, Shanghai 200093
  • Received:2003-12-12 Revised:2004-03-02 Published:2004-07-15
  • Contact: Hua Ze-Zhao

Abstract: 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).

Key words: Glass transition, Enthalpy relaxation, Ethylene glycol, Differential scanning calorimetry, Cryomicroscopy