Nanomechanics of Shear Rate-Dependent Stiffening in Micellar Electrically Conductive Polymers

TL;DR

This study uses multiscale simulations to reveal how micellar morphology and dynamics cause shear rate-dependent stiffening in conductive polymers, offering insights for designing adaptable flexible electronics.

Contribution

It uncovers the nanoscale mechanisms behind shear rate-dependent stiffening in a PANI-PAMPSA blend, highlighting the role of micellar reorganization and alignment.

Findings

Micellar morphology influences local crystallinity and entanglement.

High shear rates cause micelle dissociation and filament alignment.

Reversible stiffening occurs over three orders of shear rate magnitude.

Abstract

Electrically conducting polymers with mechanical adaptability are essential for flexible electronics, yet most suffer structural degradation under rapid deformation. In this study, multiscale coarse-grained (MSCG) simulations are used to uncover the nanoscale origins of an unusual strain-rate-dependent stiffening in a poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA)-polyaniline (PANI) blend. The self-assembled morphology consists of semi-crystalline PANI-rich micellar cores dispersed in a soft, viscoelastic PAMPSA matrix. At low shear rates, micelles migrate and coalesce into larger aggregates, enhancing local crystallinity and transient entanglement density while dissipating stress through matrix deformation. At high shear rates, micelles cannot reorganize quickly enough, leading to core dissociation and the emergence of highly aligned PANI filaments that directly bear the load, with PAMPSA serving as a weak but extended support phase. These contrasting regimes (densification-driven local alignment versus dissociation-driven global alignment) enable reversible mechanical stiffening across three orders of magnitude in shear rate. The results provide a molecular-level framework for designing solid-state polymers with tunable, rate-adaptive mechanical properties.