Dynamical properties of toluene and ortho-terphenyl confined in MCM-41 and SBA-15 mesoporous materials

We used calorimetry and neutron scattering measurements to investigate the dynamical behaviour of the molecular glass-forming liquids, toluene and ortho-terphenyl, confined in ordered mesoporous silica materials with pore diameters from 2.4 to 8.7 nm. In silica-walled porous materials, all the data demonstrate spatially heterogeneous dynamics. The pore size dependences of the calorimetric glass transition temperature T-g (which probes the long-time dynamics), as well as of the mean square displacements (which probe short-time dynamics), are dominated, on the one hand, by the interactions of the confined liquid with the surface of the pores, and on the other hand, by the finite size effects. The former effect is the key parameter for the transition in the pores smaller than 6 molecular sizes. In larger pores (pore diameter > 10 molecular diameters), the surface interaction effects are less important and finite size effects induce dynamics faster than the bulk one. Finite size effects are even amplified in grafted matrices with less attractive surfaces.