Enthalpy Relaxation Studies On The Non-linearity Of Structural Relaxation In Small Molecular Glass Systems

The structural relaxation dynamics of supercooled liquids and glasses is studied using the differential scanning calorimetry in order to understand the change of the non-linear parameter and the correlation among different dynamic parameters involved in the glass transition. Three types of glasses include pure substances and three binary mxituers. The non-linear parameter is focused together with other characteric parameters determined mainly from Tool-Narayanaswamy-Moynihan-Hodge(TNMH) equation, Kohlrausch-Williams-Watts(KWW) equation and Richert equation.The non-linear parameter decreases with increasing the fragility for the same kind of glass formers when the fragility covering a wide range by analyzing the characteric parameters of the pure liquids with different fragilities or isomers, or different functional groups, and the rule is valid for any kind of glass forming systems among polymers, inorganic and ionic liquids and metallic glasses. The rule which the non-linear parameter is usually bigger than non-exponential parameter is also found.The correlation between the dynamic parameters and the concertrations of three kinds of binary mixtures with ideal, near ideal and non-ideal mixitures are researched, the direction of deviations from the linear correlation for non-linear are all the same of the results of the non-linear parameter, the degree of deviation are affected by the mixing enthalpy.The isothermal structural relaxation of glassy triacetin and glycerol is studied by enthalpy relaxation and fitted by TNMH, KWW and Richert equations. The non-linear parameter is a function of temperature and time which increases with the aging time. The results show the fixed fitting by the Richert equation is more suitable and the non-linear parameter varies with the aging temperature. The value corresponds to the glass transition temperature is different from that is obtained by aging.The studies assist on estimating the non-linear parameter and checking on the correlation with other parameters, extrapolating the value with lower glass forming ability by the rule of binary mixtures, understanding the materials which are studied only by mixing, guiding to construct the structural materials with particular parameters, recognizing the rule of the non-linear and non-exponential parameter varying with the time and temperature during the structural relaxation below the glass temperatures, knowing the varied properties and enhancing the practical value of glass materials. The knowledge about the correlation between the non-linear parameter and glass stability can also be improved greatly.