Dielectric relaxation at the glass transition of confined N-methyl-ɛ-caprolactam

D. Daoukaki, G. Barut, R. Pelster, G. Nimtz, A. Kyritsis, and P. Pissis
Phys. Rev. B 58, 5336 – Published 1 September 1998
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Abstract

The effects of confinement on the glass transition of the nonassociating glass-forming liquid N-methyl-ɛ-caprolactam were studied in detail by means of broadband dielectric relaxation spectroscopy, 5 Hz–2 GHz, and thermally stimulated depolarization current measurements, 77–300 K. The liquid was two dimensionally confined in the pores of controlled porous glasses with mean pore diameter d=2.5, 5.0, 7.5, and 20.0 nm (Gelsil glasses) and d=4.0nm (Vycor glass) and three dimensionally confined in butyl rubber with mean droplet diameter d=7.6nm. The confined liquid is classified into two fractions: a relatively immobile interfacial layer close to the wall and the inner layer (volume liquid). For the volume liquid the α relaxation associated with the glass transition becomes faster and the glass transition temperature decreases compared to the bulk liquid. These effects increase with decreasing d and are stronger for three- than for two-dimensional confinement. They can be understood on the basis of the cooperativity concept and the configurational entropy model of Adam and Gibbs. The systematic variation of d allows the determination of the cooperativity length ξ at Tg to ξ<~1012nm.

  • Received 9 December 1997

DOI:https://doi.org/10.1103/PhysRevB.58.5336

©1998 American Physical Society

Authors & Affiliations

D. Daoukaki

  • National Technical University of Athens, Department of Physics, Zografou Campus, GR-15780 Athens, Greece

G. Barut, R. Pelster, and G. Nimtz

  • Universität zu Köln, II. Physikalisches Institut, Zülpicher strasse 77, 50937 Köln, Germany

A. Kyritsis and P. Pissis

  • National Technical University of Athens, Department of Physics, Zografou Campus, GR-15780 Athens, Greece

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Vol. 58, Iss. 9 — 1 September 1998

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