DIELECTRIC INVESTIGATIONS OF THE DYNAMIC GLASS-TRANSITION IN NANOPORES

Broadband dielectric spectroscopy (10(-2) Hz-10(9) Hz) is employed to study the dynamic glass transition of low-molecular-weight glass-formi ng liquids being confined to nanoporous sol-gel glasses with pore size s of 2.5, 5.0, and 7.5 nm. As glass-forming liquids, salol (one hydrox y group), pentylene glycol (two hydroxy groups), and glycerol (three h ydroxy groups) were chosen. We interpret the dielectric spectra in ter ms of a two-state model with dynamic exchange between a bulklike phase in the pore volume and an interfacial phase close to the pore wall. T his enables one to analyze in detail the interplay between the molecul ar dynamics in the two subsystems (bulklike and interfacial), its dyna mic exchange, and hence their growth and decline in dependence on temp erature and strength of the molecular interactions. For glycerol it is shown that a bulklike dynamic glass transition takes place in subvolu mes as small as about 1 nm.