Crystal-to-crystal transition of ultrasoft colloids under shear

TL;DR

This study demonstrates that applying shear to ultrasoft colloids near their glass transition induces a crystal-to-crystal transition from bcc to fcc structures, revealing a new method to control colloidal crystallization.

Contribution

It uncovers shear-induced crystal-to-crystal transition in ultrasoft colloids, combining experiments and simulations to reveal structural reorganization without melting.

Findings

Shear facilitates crystallization of colloidal star polymers near glass transition.

A transition from bcc to fcc crystal structure occurs with increasing shear rate.

The transition involves a sudden reorganization without intermediate melting.

Abstract

Ultrasoft colloids typically do not spontaneously crystallize, but rather vitrify, at high concentrations. Combining in-situ rheo-SANS experiments and numerical simulations we show that shear facilitates crystallization of colloidal star polymers in the vicinity of their glass transition. With increasing shear rate well beyond rheological yielding, a transition is found from an initial bcc-dominated structure to an fcc-dominated one. This crystal-to-crystal transition is not accompanied by intermediate melting but occurs via a sudden reorganization of the crystal structure. Our results provide a new avenue to tailor colloidal crystallization and crystal-to-crystal transition at molecular level by coupling softness and shear.