Glass transition in 2- and 3-dimensionally confined liquids

Broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents (TSDC) measurements were employed to investigate effects of confinement on the glass transition of the hydrogen bonded liquid propylene glycol (PG) and the non-associating liquid N-methyl-epsilon-caprolactam (NMEC). The liquids were confined 2-dimensionally 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 confined 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 layer and liquid). With decreasing d the alpha relaxation associated with the glass transition of the liquid becomes faster and broader and the 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 less than or equal to 12 nm for NMEC. (C) 1998 Elsevier Science B.V. All rights reserved.