INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 14 (2002) 5699–5709 PII: S0953-8984(02)30298-4 Properties of a confined molecular glass-forming liquid Victor Teboul 1 and Christiane Alba Simionesco Laboratoire de Chimie Physique, UMR 8000, Universit´ e de Paris Sud, Bat. 349, 91405 Orsay cedex, France Received 31 October 2001, in final form 20 March 2002 Published 30 May 2002 Online at stacks.iop.org/JPhysCM/14/5699 Abstract We use molecular dynamics (MD) simulations to investigate the modification of the dynamic and static properties of liquid toluene when confined in cylindrical mesopores a few molecular diameters across. Due to the strong influence of the substrate on the dynamics of the confined liquid, we choose a procedure where no additional thermal interactions between the wall and the liquid are taken into account. We observe the characteristic oscillations of molecular density profiles (layering) when temperature and pore size are changed. Mean square displacements and intermediate incoherent scattering functions of the centre of mass of the molecules are calculated as functions of different distances from the wall along the principal axis of the pore z and along the perpendicular x - and y -directions. At 200 K the relaxations of the two correlation functions slow down by one order of magnitude as compared to the bulk, with a slightly more pronounced slowing down in the x -direction. This slowing down increases strongly when the wall is approached. However, we do not observe any layer- specific dependence of the dynamics, but instead a continuous change. When the molecules are arrested near the wall in the time window (1 ns) of the simulations, we find hopping processes. 1. Introduction When a liquid is confined into a pore a few molecular diameters across, its properties are deeply modified. The cooperative length postulated by most glass transition theories [1] in order to explain the formidable increase of the viscosity near the glass transition will not be able to extend to distances greater than the pore diameter. This effect may then lead to a different dynamical regime, and then to indirect information on this length scale. Unfortunately, reality is more complex and the limited length scale is not the only mechanism to take into account when a supercooled liquid is introduced into a pore: the dimensionality can be changed from three to one dimension (for a tube), finite-size effects appear, interactions with the surface may lead to 1 Permanent address: Laboratoire de Physique des Mat´ eriaux et Applications, UMR 6136, Universit´ e d’Angers, 2 Boulevard Lavoisier, 49045 Angers cedex, France. 0953-8984/02/235699+11$30.00 © 2002 IOP Publishing Ltd Printed in the UK 5699