Mobility of Molecules in Liquids near the Glass Temperature

摘要

A theory for the molecular motion in liquids is formulated. It treats the system as a series of molecular shells bound elastically to each other and to a central molecule. The vibrations of this system are analyzed approximately in an effort to find the probability that the central molecule will be left in a hole large enough so it can move to a new position. It is found that the jump frequency of the molecules obeys an equation of the form exp (mdash;E/kT) at high temperatures but conforms to the WLF equation at low temperatures. The anomalous behavior of liquids near the glass temperature is shown to result from the fact that a great deal of cooperation among adjacent molecules must occur if a molecule is to move at low temperatures. The molecular parameters needed to fit the experimental data available are found to be of reasonable magnitude. The influence of various factors such as molecular size, weight and attraction are also discussed. It is concluded that the glass transition is similar in high and low molecular weight substances and is not a property peculiar to macromolecules.