Mechanics of an Asymmetric Hard--Soft Lamellar Nanomaterial

TL;DR

This study investigates the structure and mechanical behavior of highly asymmetric soft-hard lamellar nanomaterials made from miktoarm star block copolymers, revealing how layer thickness influences deformation and damage mechanisms.

Contribution

It introduces a new class of thermodynamically stable asymmetric lamellar nanomaterials with tunable mechanical properties based on layer thickness variations.

Findings

Thinner lamellae show kinks and cavitation in soft layers.

Thicker lamellae exhibit cavitation in both soft and hard layers.

Damage involves shear deformation and cavity formation.

Abstract

Nanolayered lamellae are common structures in nanoscience and nanotechnology, but most are nearly symmetric in layer thickness. Here, we report on the structure and mechanics of highly asymmetric and thermodynamically stable soft--hard lamellar structures self-assembled from optimally designed PS1-(PI-b-PS2)3 miktoarm star block copolymers. The remarkable mechanical properties of these strong and ductile PS (polystyrene)-based nanomaterials can be tuned over a broad range by varying the hard layer thickness while maintaining the soft layer thickness constant at 13 nm. Upon deformation, thin PS lamellae (\textless{}100 nm) exhibited kinks and predamaged/damaged grains, as well as cavitation in the soft layers. In contrast, deformation of thick lamellae (\textgreater{}100 nm) manifests cavitation in both soft and hard nanolayers. In situ tensile-SAXS experiments revealed the evolution of cavities during deformation and confirmed that the damage in such systems reflects both plastic deformation by shear and residual cavities. The aspects of the mechanics should point to universal deformation behavior in broader classes of asymmetric hard--soft lamellar materials, whose properties are just being revealed for versatile applications.