Can adding oil control domain formation in binary amphiphile bilayers?

TL;DR

This study uses a mean-field model to show how adding oil of specific chain lengths can influence the structure and stability of domain boundaries in binary amphiphile bilayers, potentially allowing control over domain size.

Contribution

It demonstrates how oil molecules with chain lengths close to shorter amphiphiles can smooth bilayer boundaries, offering a new way to control domain formation in bilayers.

Findings

Oil of optimal chain length reduces bilayer boundary surface area.

Short oil molecules distribute evenly, causing minimal structural change.

Long oil molecules swell the thicker domain, increasing curvature.

Abstract

Bilayers formed of two species of amphiphile of different chain lengths may segregate into thinner and thicker domains composed predominantly of the respective species. Using a coarse-grained mean-field model, we investigate how mixing oil with the amphiphiles affects the structure and thickness of the bilayer at and on either side of the boundary between two neighbouring domains. In particular, we find that oil molecules whose chain length is close to that of the shorter amphiphiles segregate to the thicker domain. This smooths the surface of the hydrophobic bilayer core on this side of the boundary, reducing its area and curvature and their associated free-energy penalties. The smoothing effect is weaker for oil molecules that are shorter or longer than this optimum value: short molecules spread evenly through the bilayer, while long molecules swell the thicker domain, increasing the surface area and curvature of the bilayer core in the interfacial region. Our results show that adding an appropriate oil could make the formation of domain boundaries more or less favourable, raising the possibility of controlling the domain size distribution.