Finite-size and surface effects on the glass transition of liquid toluene confined in cylindrical mesopores

Some of the most regular porous silicates (MCM-41 and SBA-15), with several different pore diameters from 2.4 to 8.7 nm, are used to study the van der Waals fragile liquid toluene in confined geometry. We measure two major macroscopic signatures of a glass transition, i.e., a discontinuous change in the heat capacity and in the thermal expansion, by adiabatic calorimetry and neutron scattering experiments. A nontrivial size dependence of the glass transition features, most notably a nonmonotonic variation of the mean glass transition temperature, is observed. The range of the glass transition is found extremely broad. This supports the notion of competition between surface boundary conditions and cutoff or finite-size effects. (C) 2002 American Institute of Physics.