title: Influence of molecular structure on the dynamics of supercooled van der Waals liquids.
abstract: Dielectric spectroscopy was carried out on the van der Waals liquid, 1,1(')-di(4-methoxy-5-methylphenyl)cyclohexane (BMMPC) in the supercooled state at pressures up to 218 MPa. The excess wing in this type-A glass former exhibits a response to pressure and temperature changes that is identical to that of the primary structural relaxation peak, indicating that the two processes reflect correlated molecular motions. Under no conditions was a distinct secondary peak observed in BMMPC, unlike the structurally very similar BMPC [1,1(')-bis(p-methoxyphenyl)cyclohexane]. However, the pressure dependences of both the glass temperature and fragility for the two materials are very close. The fragility is a decreasing function of pressure, although there is no concomitant narrowing of the relaxation peak. The pressure dependence of the relaxation times could be described as a simple volume-activated process, with the activation volume at the glass transition having the same magnitude as the molar volume.
authors.affiliation: Chemistry Division, Code 6120, Naval Research Laboratory, Washington, DC 20375-5342, USA.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Casalini
authors.forename: Marian
authors.initials: M
authors.lastname: Paluch
authors.forename: C Michael
authors.initials: CM
authors.lastname: Roland