GLASS-TRANSITION IN 2-DIMENSIONALLY AND 3-DIMENSIONALLY CONFINED LIQUIDS

Broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents (TSDC) measurements were employed to investiga te effects of confinement on the glass transition of the hydrogen bond ed liquid propylene glycol (PG) and the non-associating liquid N-methy l-epsilon-caprolactam (NMEC). The liquids were confined 2-dimensionall y in the pores of porous glasses with mean pore diameter 2.5 less than or equal to d less than or equal to 20.0 nm and 3-dimensionally confi ned in butyl rubber with mean droplet diameter 7 less than or equal to d less than or equal to 11 nm. The data provide evidence for both the cooperativity concept and the existence of two states (interfacial la yer and liquid). With decreasing d the alpha relaxation associated wit h the glass transition of the liquid becomes faster and broader and th e glass transition temperature decreases. These effects are larger for 3- than for 2-dimensional confinement. The cooperativity length, xi, at T-g is determined to xi less than or equal to 6 nm for PG and xi le ss than or equal to 12 nm for NMEC. (C) 1998 Elsevier Science B.V. All rights reserved.