Fluid–wall interactions effects on the dynamical properties of confined orthoterphenyl

We have investigated the dynamics of fragile glass forming orthoterphenyl confined in nanoporous materials with different surface properties. The dynamics on the nanosecond timescale were probed with neutron spin echo measurements. The intermediate scattering functions were fitted using a stretched exponential and a background. This background, due to molecules forming an interfacial layer at the surface of the pore that are immobile at the nanosecond time scale, depends on the surface properties of the porous materials and increases with decreasing temperature. The dynamics of the confined liquid depends on fluid–wall interactions: the dynamics are slower in a weakly attractive silica-walled material with 7.1 nm pores (∼9 molecular diameters) than in a hydrophobic material with 6.3 nm pores (∼8 molecular diameters). Adsorption times of 1 μs and 690 ns at 298 and 323 K for oTP confined in silica-walled nanoporous materials were calculated from nuclear magnetic resonance field cycling relaxometry experiments.