Revealing spatially heterogeneous relaxation in a model nanocomposite

Shiwang Cheng, Stephen Mirigian, Jan Michael Y. Carrillo, Vera Bocharova, Bobby G. Sumpter, Kenneth S. Schweizer, Alexei P. Sokolov

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Article number194704
JournalJournal of Chemical Physics
Volume143
Issue number19
DOIs
StatePublished - Nov 21 2015

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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