Cooperativity and heterogeneity of the dynamics in nano-confined liquids

We have measured the time resolved Stokes shift of the probe molecule quino xaline in glass-forming solvents of different polarities under the conditio n of geometrical confinement, for which this solvation dynamics technique i s particularly suitable. While solvation probes the local dielectric relaxa tion in polar liquids, it is associated with the local mechanical responses in non-polar systems. The effect of porous glasses on the relaxations of s upercooled liquids is strongly dependent on the surface chemistry and can b e rationalized on the basis of the cooperativity concept. We also present e vidence for the heterogeneous nature of relaxation dynamics in nano-confine d liquids. In a further experiment, in which the chromophores are selective ly positioned at the liquid/solid interface, we observe that the relaxation in the immediate vicinity of the glass surface can be qualitatively simila r to the bulk behaviour.