Transient rheology and morphology in sheared nanolayer polymer films

TL;DR

This study investigates how nanolayered polystyrene/poly(methyl methacrylate) films behave under shear, revealing that nanolayers dewet and form complex morphologies, affecting their rheological properties.

Contribution

It provides new insights into the transient rheology and morphological evolution of nanolayered polymer films under shear, highlighting the effects of layer thickness and strain.

Findings

Nanolayered films show decreasing viscosity over time, unlike micron-sized layers.

Nanolayers dewet and form lamellar and nodular morphologies.

Droplet size distribution was characterized from microscopic images.

Abstract

The rheology of coextruded layered films of polystyrene/poly(methyl methacrylate) (PS/PMMA) has been studied with small and large amplitude oscillations at a temperature above their glass transition. While the complex viscosity remains constant over the experimental time window for the micron-sized layered films, a decrease has been observed for the nanolayered films. The rheological behavior has then been correlated to the morphological evolution of the multilayer films: while the nanolayers dewet. Layer breakup followed by retraction and coalescence leading to a lamellar-like blend morphology succeeded by a nodular-like morphology has been evidenced in the nanolayer films, for all compositions and conditions tested. The analysis of the microscopic images of the film cross-sections also provided the droplet size distribution. The nodular morphology is achieved more rapidly when the initial layers are the thinnest at low strains, while at high strains the formation of these droplets is prevented.