Anomalous Molecular Weight Dependence Reveals the Origin of Mechanical Enhancement in Polymer Nanocomposite

TL;DR

This study uncovers how anomalous molecular weight effects at polymer interfaces lead to significant mechanical reinforcement in nanocomposites, challenging traditional assumptions about molecular weight's role.

Contribution

It reveals the unexpected chain elongation and mechanical enhancement mechanisms in bimodal molecular weight polymer nanocomposites, introducing new insights into interface-driven property improvements.

Findings

Shear modulus increases up to 103 times with lower average MW.

Interfacial polymers exhibit chain elongation promoting network formation.

Mechanical reinforcement occurs when short chains are much shorter than long chains, with a universal stretching factor of 2.3.

Abstract

Polymers at the interface exhibit frustrated chain conformation distinct from the bulk, impacting particle dispersion and properties of polymer nanocomposites (PNCs). Utilizing bimodal molecular weight (MW) PNCs, we observed unusual chain elongation of interfacial polymers, which promotes networked structures at low particle loadings. Paradoxically, reducing the average MW in bimodal PNCs significantly enhances the shear modulus by up to 103 times, challenging the conventional preference for higher MW in property enhancement. The mechanical reinforcement, aided by stretched chains, manifests when the short chain is substantially shorter than the long chain (Rg ratio >~2), indicating a universal stretching factor of 2.3.