Heterogeneous relaxation dynamics of nano-confined salol probed by DMA

We present novel low-frequency (0.1 Hz–50 Hz) measurements of the complex elastic susceptibility of the glass-forming liquid salol confined to nanoporous Vycor glass. Our data can be perfectly interpreted with the assumption of a radial distribution of Vogel-Fulcher temperatures T₀(r) inside the pores, resulting from an increase of the molecular relaxation time with decreasing distance from the rough pore surface as recently found by computer simulations (Scheidler et al., Europhys. Lett. 59, 701 (2002)). The results show for the first time, that the dynamic elastic response is extremely sensitive for separating confinement-induced acceleration effects of the molecular dynamics and surface-induced slowing-down due to rough pore interfaces.