Controlling the shape and topology of two-component colloidal membranes

TL;DR

This paper demonstrates how doping colloidal membranes with short rods can control their shape and topology, leading to complex structures like saddle surfaces and sponge phases, revealing new insights into membrane reconfiguration.

Contribution

It introduces a method to manipulate membrane shape and topology through compositional doping, supported by theoretical modeling and experimental observations.

Findings

Doping induces saddle-shaped and complex topological structures.

Formation driven by Gaussian modulus controlled by rod fraction.

Observation of a sponge-like phase at long times.

Abstract

Changes in the geometry and topology of self-assembled membranes underlie diverse processes across cellular biology and engineering. Similar to lipid bilayers, monolayer colloidal membranes have in-plane fluid-like dynamics and out-of-plane bending elasticity. Their open edges and micron length scale provide a tractable system to study the equilibrium energetics and dynamic pathways of membrane assembly and reconfiguration. Here, we find that doping colloidal membranes with short miscible rods transforms disk-shaped membranes into saddle-shaped surfaces with complex edge structures. The saddle-shaped membranes are well-approximated by Enneper's minimal surfaces. Theoretical modeling demonstrates that their formation is driven by increasing positive Gaussian modulus, which in turn is controlled by the fraction of short rods. Further coalescence of saddle-shaped surfaces leads to diverse topologically distinct structures, including catenoids, tri-noids, four-noids, and higher order structures. At long time scales, we observe the formation of a system-spanning, sponge-like phase. The unique features of colloidal membranes reveal the topological transformations that accompany coalescence pathways in real time. We enhance the functionality of these membranes by making their shape responsive to external stimuli. Our results demonstrate a novel pathway towards control of thin elastic sheets' shape and topology -- a pathway driven by the emergent elasticity induced by compositional heterogeneity.