THE COOPERATIVE MOLECULAR DYNAMICS AND NONLINEAR PHENOMENA

摘要

One of the most widely used theories of the glass forming liquids is the theory of Adam and Gibbs. At the macroscopical level the theory successfully relates the temperature dependence of relaxation times to the configuration entropy. An extension of this theory at molecular level has been discussed here. Two equations for measuring the size of the cooperatively rearranging region are suggested, one from the kinetic and the other from the thermodynamic properties of the liquids. From the thermodynamic equation it follows that the basic molecular units in glass forming liquids are not molecules or monomer segments, bul fragment of them, known in thermodynamic as "beads." In polymers with small side-chain groups a bead is formed by one main chain atom with the groups attached to it. The estimated number of the configurations within a cooperatively rearranging region is larger than that in the solid-like Adam-Gibss cooperatively rearranging region with only two configurations. It follows from this fact that the cooperatively rearranging region is a liquid unit, and that a statistical independence in surmounting the individual potential barriers by the basic molecular units may exist. A molecular interpretation of the Fragility Classification System, the apparent activation energy and the relaxation volume on the basis of the size of the cooperatively rearranging region is given. The relations between the kinetic and the thermodynamic measure of fragility are suggested. A possibility for the existence of analogs of the cooperatively rearranging region in nonlinear dielectric relaxation is discussed. Experimental results for inorganic glasses and polymer are examined.