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Issue 2, 2016
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Entropic forces stabilize diverse emergent structures in colloidal membranes

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The depletion interaction mediated by non-adsorbing polymers promotes condensation and assembly of repulsive colloidal particles into diverse higher-order structures and materials. One example, with particularly rich emergent behaviors, is the formation of two-dimensional colloidal membranes from a suspension of filamentous fd viruses, which act as rods with effective repulsive interactions, and dextran, which acts as a condensing, depletion-inducing agent. Colloidal membranes exhibit chiral twist even when the constituent virus mixture lacks macroscopic chirality, change from a circular shape to a striking starfish shape upon changing the chirality of constituent rods, and partially coalesce via domain walls through which the viruses twist by 180°. We formulate an entropically-motivated theory that can quantitatively explain these experimental structures and measurements, both previously published and newly performed, over a wide range of experimental conditions. Our results elucidate how entropy alone, manifested through the viruses as Frank elastic energy and through the depletants as an effective surface tension, drives the formation and behavior of these diverse structures. Our generalizable principles propose the existence of analogous effects in molecular membranes and can be exploited in the design of reconfigurable colloidal structures.

Graphical abstract: Entropic forces stabilize diverse emergent structures in colloidal membranes

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Article information

14 Aug 2015
08 Oct 2015
First published
09 Oct 2015

Soft Matter, 2016,12, 386-401
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Entropic forces stabilize diverse emergent structures in colloidal membranes

L. Kang, T. Gibaud, Z. Dogic and T. C. Lubensky, Soft Matter, 2016, 12, 386
DOI: 10.1039/C5SM02038G

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