Confinement induces both higher free volume and lower molecular mobility in glycerol

We report measurements of the local free volume and mobility of a glass-forming liquid (glycerol) confined in a mesoporous silica glass. The lower molecular mobility in confinement, measured by neutron scattering spectroscopy, is accompanied by a higher mean free volume size between molecules, measured by positron annihilation lifetime spectroscopy. The confined liquid appears to be perturbed to such an extent that the normally observed free volume/mobility relationship is reversed. This study shows that these effects originate locally at a molecular level. (C) 2008 American Institute of Physics.