Glass transition temperature molecular reorientation dynamics

Classical methods are designed to obtain thermodynamic and transport information, for example molar volume, density, viscosity, and surface tension. The effects of pressure and temperature on these properties can also be evaluated, and thus phase transition information such as melting points and glass transition temperatures. If molecular dynamics (in contrast to Monte Carlo) is used, data relating to reorientation of molecules, self-diffusion and residence times are all available. Information can also be obtained from the simulation equations on the contribution made by kinetic, coulombic, intramolecular and dispersion energies to the total potential energy. However, because the charges are fixed and there is no explicit wavefunction included in the classical methods, no electronic information can be obtained. 

Specific applications of DIRLD spectroscopy are presented for several polymer systems to demonstrate the types of information obtainable from this powerful rheo-optical characterization technique. A DIRLD study of atactic polystyrene revealed the existence of highly localized motion of various molecular constituents induced by a macroscopic dynamic strain.It was discovered the rate of reorientational motion of the polystyrene backbone differs considerably from that of the phenyl side groups. The reorientation direction of the phenyl side groups changes dramatically as the temperature of the system is raised above the glass transition temperature. This result may be interpreted as the onset of a new submolecular... 

As the dielectric technique probes molecular mobility, through the reorientation of dipoles, the observed shift to higher temperatures means that the molecular dynamics associated with the glass transition, becomes more hindered in the copolymer. The... 

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