Surface freezing and a two-step pathway of the isotropic-smectic phase transition in colloidal rods

TL;DR

This study reveals that in colloidal rod systems, surface freezing occurs before the bulk isotropic-smectic transition, involving a two-step process with surface wetting and layer nucleation.

Contribution

It uncovers a two-step kinetic pathway for the isotropic-smectic transition, highlighting the role of surface-induced smectic phases in colloidal rods.

Findings

Surface freezing precedes bulk transition.

A metastable isotropic-nematic interface forms first.

Smectic layers nucleate at the surface and grow into the bulk.

Abstract

We study the kinetics of the isotropic-smectic phase transition in a colloidal rod/polymer mixture by visualizing individual smectic layers. First, we show that the bulk isotropic-smectic phase transition is preceded by a surface freezing transition in which a quasi two-dimensional smectic phase wets the isotropic-nematic interface. Next, we identify a two step kinetic pathway for the formation of a bulk smectic phase. In the first step a metastable isotropic-nematic interface is formed. This interface is wetted by the surface induced smectic phase. In the subsequent step, smectic layers nucleate at this surface phase and grow into the isotropic bulk phase.