Search for Elementary Rearrangement Process and Investigation of Irreversible Structural Relaxation in Simple-Molecular Liquids

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1) beta-glass transition as well as alpha-one were found by an adiabatic calorimetry to occur in the supercooled liquid state of 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane, omicron-terphenyl, propene carbonate and dibutylphthalate. Further, in the plastically crystalline state of cyclohexanol, there were two sets of alpha-and beta-glass transitions and another glass transition found to occur. A possibility was suggested that plural modes of molecular rearrangement motions coupled in liquid were decoupled from each other through the positional ordering of molecules.2) alpha-relaxation processes under constant temperature condition were studied calorimetrically by the temperature jump method for glycerol, propylene glycol, 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane and dibutylphthalate with different fragilities from each other. The relaxation processes were characterized in terms of the nonexponentiality parameter beta of stretched exponential function. A strong correlation was found to exist between the fragility m and the nonlinearity delta=dbeta/dDELTA_jT of relaxation function to the temperature jump. The presence of the correlation was also confirmed by a computer simulation of the ireversible relaxation process based on a thermal activation model.3) The similar enthalpy relaxation processes were tracked by the temperature jump method for fluorene-dibenzofuran solid solutions. The nonexponentiality parameter beta was constant independently of DELTA_jT for each conpound. This result is quite in contrast to that in supercooled liquid, demonstrating that the nonlinearity found in liquid is attributed mainly to a non-Arrhenius property of the average relaxation times.4) A new crystallization process due to the aggregation of homogeneous crystal embryos/nuclei was discovered in omicron-terphenyl and salol in their respective glass transition regions. The growth rate was found to be determined by the beta-relaxation rate but not by the alpha-one commonly recognized.