Investigation of the cause of the glass transition and size dependent melting behavior
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Abstract
In this thesis, the idea -- that the dramatic reduction in molecular mobility or dynamic slowdown in a supercooled liquid during cooling from above Tg occurs because of the increasing length scale of heterogeneous subregions, or the Cooperatively Rearranging Regions proposed by Adam and Gibbs – is evaluated. The structural recovery of thermo sensitive colloidal glassy systems under constant mass concentration after temperature jumps are investigated and compared with those in molecular glasses from the aspect of Kovacs protocol. Moreover, a systematic study of the temperature dependence of the dynamics of the thermal sensitive colloidal system for different weight concentrations is performed and the dynamic fragility index m is determined. Results obtained from diffusing wave spectroscopy show reasonable consistency with those obtained from conventional rheological measurement. In addition to investigate the glass transition behavior, the size dependent melting behaviors of trinitrotoluene confined in the nano-scale pores of controlled pore glasses are also studied by differential scanning calorimetry. Both of the melting temperature and the heat of fusion of confined nano-crystals decrease with decreasing pore size and the results are consistent with model prediction.