ROLE OF MOLECULAR-REORIENTATION IN THE VITRIFICATION OF MOLECULAR LIQUIDS - A MONTE-CARLO STUDY OF THE LIQUID AND GLASSY STATES OF 2,2-DIMETHYLBUTANE

The liquid and the glassy phases of 2,2-dimethylbutane have been inves tigated by isothermal isobaric ensemble Monte Carlo simulation. Thermo dynamic properties and radial distribution functions for both the liqu id and the glass have been obtained. The radial distribution functions have been classified into three types based on the accessibility of t he group. It has been shown that the structure of the liquid and the g lass can be understood in terms of the above classification of the rad ial distribution functions. Molecular reorientation plays an important role in the structural rearrangement accompanying glass formation. As much as 36% of the contribution to the increase in the intermolecular interaction energy on vitrification is due to the reorientation of th e neighbouring pairs of molecules. The observed changes in the dimeris ation energy and the bonding energy distribution function are consiste nt with the observed structural changes.