Self-assembly of 2D membranes from mixtures of hard rods and depleting polymers

TL;DR

This study combines simulations and experiments to understand how hard rods and depleting polymers self-assemble into stable 2D membranes, revealing the conditions for membrane stability and the role of molecular fluctuations.

Contribution

It provides new insights into the molecular forces and conditions that lead to the formation of stable 2D membranes from hard rods and polymers, supported by both simulations and experimental validation.

Findings

Membranes are stable above a critical rod aspect ratio.

Membranes are stable below a critical depletion length scale.

Molecular protrusion fluctuations alone can stabilize membranes.

Abstract

We elucidate the molecular forces leading to assembly of two dimensional membrane-like structures composed of a one rod-length thick monolayer of aligned rods from an immiscible suspension of hard rods and depleting polymers. We perform simulations which predict that monolayer membranes are thermodynamically stable above a critical rod aspect ratio and below a critical depletion interaction length scale. Outside of these conditions alternative structures such as stacked smectic columns or nematic droplets are thermodynamically stable. These predictions are confirmed using an experimental model system of virus rod-like molecules and non-adsorbing polymer. Our work demonstrates that collective molecular protrusion fluctuations alone are sufficient to stabilize membranes composed of homogenous rods with simple excluded volume interactions.