Short Time and Structural Dynamics in Polypropylene Glycol Nanocomposite

TL;DR

This study investigates how silica nanoparticles affect the microscopic and segmental dynamics of polypropylene glycol, revealing suppressed displacements but faster motions in nanocomposites and discovering a new local dynamic process at low temperatures.

Contribution

It provides new insights into the influence of silica nanoparticles on polymer dynamics and identifies a previously unknown local process at low temperatures.

Findings

Displacements are suppressed at certain relaxation temperatures.

Motions are faster in nanocomposites due to lower packing density.

A new local dynamic process is observed at very low temperatures.

Abstract

The dynamics of polypropylene glycol, both neat and attached to silica nanoparticles, were investigated using elastic neutron backscattering and dielectric spectroscopy. The mean square displacement measured by the former is suppressed by the particles at temperatures corresponding to a dielectric secondary relaxation (that involves only a portion of the repeat unit) and the segmental relaxation (glass transition). Despite the suppression of the displacements, the motions are faster in the nanocomposite, primarily due to poorer packing (lower density) at the particle interface. At very low temperatures we discovered a new dynamic process in the polymer. Reflecting its very local nature, this process is unaffected by attachment of the chains to the silica.