Tuning the Mechanical Properties in Model Nanocomposites: Influence of the Polymer-Filler Interfacial Interactions

TL;DR

This study investigates how polymer-filler interfacial interactions affect dispersion and mechanical reinforcement in PS/silica nanocomposites, revealing that local interactions influence reinforcement at high silica loadings, while long-range effects dominate at low loadings.

Contribution

It provides a comparative analysis of un-grafted and grafted silica in PS nanocomposites, highlighting the role of interfacial interactions on mechanical properties and filler network formation.

Findings

Reinforcement at low silica volume fraction is dominated by long-range effects.

High silica volume fraction leads to a connected network increasing reinforcement.

Grafting reduces local particle/particle interactions, affecting mechanical response.

Abstract

This paper presents a study of the polymer-filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS) / silica nanocomposites by direct comparison of two model systems: un-grafted and PS-grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining Small Angle Neutron Scattering (SANS) measurements and Transmission Electronic Microscopic (TEM) images. The mechanical properties were studied over a wide range of deformation by plate/plate rheology and uni-axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size non-connected aggregates and the materials exhibit a solid-like behavior independent of the local polymer/fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle/particle interactions and lower with grafting likely due to deformation of grafted polymer.