Molecular Dynamics in grafted layers of poly(dimethylsiloxane) (PDMS)

TL;DR

This study uses dielectric relaxation spectroscopy to investigate how the molecular dynamics of PDMS films change with thickness, revealing significant acceleration below the radius of gyration due to chain confinement effects.

Contribution

It provides new insights into the thickness-dependent molecular dynamics of grafted PDMS layers, highlighting the impact of chain confinement on relaxation behavior.

Findings

Faster molecular dynamics for d < Rg by up to three orders of magnitude.

Decrease in Vogel temperature T0 and glass transition temperature Tg for thin films.

Crystallization observed in films both above and below Rg.

Abstract

Dielectric relaxation spectroscopy 10^-1 Hz to 10^6 Hz) is employed to study the molecular dynamics of poly(dimethylsiloxane) (PDMS, Mw=1.7 10^5 g/mol and Mw=9.6 10^4 g/mol as grafted films with thicknesses d below and above the radius of gyration Rg. For d smaller than Rg the molecular dynamics becomes faster by up to three orders of magnitude with respect to the bulk resulting in a pronounced decrease of the Vogel temperature T0 and hence the calorimetric glass transition temperature Tg. For d larger than Rg the molecular dynamics is comparable to that of the bulk melt. The results are interpreted in terms of a chain confinement effect and compared with the findings for low molecular eight glass forming liquids contained in nanoporous glasses and zeolites. Crystallization effects - well known for PDMS - are observed for films of thicknesses above and below Rg.