Laterally structured ripple and square phases with one and two dimensional thickness modulations in a model bilayer system

Debnath, Ananya and Thakkar, Foram M and Maiti, Prabal K and Kumaran, V and Ayappa, KG (2014) Laterally structured ripple and square phases with one and two dimensional thickness modulations in a model bilayer system. In: SOFT MATTER, 10 (38). pp. 7630-7637.

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Abstract

Molecular dynamics simulations of bilayers in a surfactant/co-surfactant/water system with explicit solvent molecules show formation of topologically distinct gel phases depending upon the bilayer composition. At low temperatures, the bilayers transform from the tilted gel phase, L beta', to the one dimensional (1D) rippled, P beta' phase as the surfactant concentration is increased. More interestingly, we observe a two dimensional (2D) square phase at higher surfactant concentration which, upon heating, transforms to the gel L beta' phase. The thickness modulations in the 1D rippled and square phases are asymmetric in two surfactant leaflets and the bilayer thickness varies by a factor of similar to 2 between maximum and minimum. The 1D ripple consists of a thinner interdigitated region of smaller extent alternating with a thicker non-interdigitated region. The 2D ripple phase is made up of two superimposed square lattices of maximum and minimum thicknesses with molecules of high tilt forming a square lattice translated from the lattice formed with the thickness minima. Using Voronoi diagrams we analyze the intricate interplay between the area-per-head-group, height modulations and chain tilt for the different ripple symmetries. Our simulations indicate that composition plays an important role in controlling the formation of low temperature gel phase symmetries and rippling accommodates the increased area-per-head-group of the surfactant molecules.

Item Type:	Journal Article
Publication:	SOFT MATTER
Publisher:	ROYAL SOC CHEMISTRY
Additional Information:	Copy right for this article belongs to the ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND.
Department/Centre:	Division of Mechanical Sciences > Chemical Engineering Division of Physical & Mathematical Sciences > Physics
Date Deposited:	08 Nov 2014 05:18
Last Modified:	08 Nov 2014 05:18
URI:	http://eprints.iisc.ac.in/id/eprint/50183

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