Abstract
The detailed nature of spatially heterogeneous dynamics of glycerol-silica nanocomposites is unraveled by combining dielectric spectroscopy with atomistic simulation and statistical mechanical
theory. Analysis of the spatial mobility gradient shows no “glassy” layer, but the α-relaxation time
near the nanoparticle grows with cooling faster than the α-relaxation time in the bulk and is ∼20
times longer at low temperatures. The interfacial layer thickness increases from ∼1.8 nm at higher
temperatures to ∼3.5 nm upon cooling to near bulk Tg. A real space microscopic description of the
mobility gradient is constructed by synergistically combining high temperature atomistic simulation
with theory. Our analysis suggests that the interfacial slowing down arises mainly due to an increase
of the local cage scale barrier for activated hopping induced by enhanced packing and densification
near the nanoparticle surface. The theory is employed to predict how local surface densification can be manipulated to control layer dynamics and shear rigidity over a wide temperature range.
