Conformational rearrangements in thin films of polydimethylsiloxane melt

TL;DR

This study uses synchrotron X-ray reflectivity to investigate how polydimethylsiloxane (PDMS) melts rearrange near silica surfaces, revealing a low-density, quasi-immobilized layer whose formation depends on molecular weight.

Contribution

It provides detailed insights into the formation and characteristics of interfacial layers in PDMS melts, highlighting the influence of molecular weight on rearrangement dynamics.

Findings

A quasi-immobilized low-density layer forms near silica surfaces.

Layer formation is rapid for low molecular weight PDMS.

Higher molecular weight PDMS takes 5-10 hours to form the layer.

Abstract

Synchrotron X-ray reflectivity (XRR) confirms the formation of a quasi-immobilized layer in thin films of polydimethylsiloxane (PDMS) melts near silica surfaces. This layer (40-60A) has a lower density than the bulk value, and its thickness varies slightly with PDMS molecular weight. Formation of this layer is very rapid for PDMS melts with low molecular weights (below entanglement limit for these molecules) but takes 5-10 hours for higher molecular weights (close to and above their entanglement value).