Morphology, Molecular Dynamics, and Interfacial Phenomena in Systems Based on Silica Modified by Grafting Polydimethylsiloxane Chains and Physically Adsorbed Polydimethylsiloxane

Abstract

This study deals with effects on structure, molecular mobility, and interfacial polymer–nanoparticles (NPs), arising from modification of silica NPs by grafting of small polydimethylsiloxane (PDMS) chains, via siloxane bond breaking, in combination with polymer molecular weight, Wm, both below and above the entanglement threshold (Wm,e ≈ 8k). According to infrared (IR), upon grafting of PDMS, the coverage of surface silica hydroxyls is almost complete (100%) and uniform for short chains, whereas it is lower, ∼60%, for longer chains (non-uniform). The combination of results by nitrogen adsorption–desorption and calorimetry (differential scanning calorimetry, DSC) indicates that the nanoparticle surface accessibility by the polymer is dynamic, as it changes non-monotonically with the gradual increasing of polymer adsorption. The grafted chains show no mobility (rigid or dead layer) neither by DSC nor by broadband dielectric spectroscopy (BDS), due to the severe fragmentation during the siloxane breaking pro...