How many molecules form a liquid?

Abstract

Broad-band dielectric spectroscopy is employed to study the molecular dynamics of (dielectrically active) glass-forming liquids which are confined to (dielectrically inactive) zeolites and nanoporous glasses. For the H-bond-forming liquid ethylene glycol (EG) embedded in zeolites of different sizes and topologies one observes a sharp transition from a single-molecule dynamics (with an Arrhenius-type temperature dependence) to that of a liquid (with a temperature dependence of the mean relaxation rate following a Vogel-Fulcher-Tammann (VFT) law): while EG in silicalite (showing a single-molecule relaxation) has a coordination number of four, EG in zeolite beta or -5 has a coordination number of five and behaves like a bulk liquid.