Inducing the Two-Dimensional Ripple Phase In Surfactant Bilayer Membranes

Inducing the  two-dimensional ripple phase in surfactant bilayer membranes

Ananya Debnath*, Foram Thakkar^$ , K. G. Ayappa , V. Kumaran  and Prabal K Maiti¹

Department of Chemical Engineering, Indian Institute of Science Bangalore, 560012, India

¹Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore 560012, India

Surfactants can self assemble into a wide variety of thermodynamically stable and topologically distinct mesoscopic structures. The lamellar phase which consists of alternating stacks of water and surfactant are similar in structure to biological membranes containing lipids. Rippling of the lamellar phase is observed in the pretransition region of the gel to liquid crystalline transition. The factors that control the formation of the ripple and the associated symmetry are unresolved. In this presentation we illustrate using all atom molecular dynamics simulations of surfactant bilayers, that the tilted L_b′ phase can be transformed to the 1D rippled P_b′  which upon further increase in the surfactant composition transforms to the rippled phase with 2D square symmetry. The atomistic perspective emerging from the molecular dynamics study indicates that increasing the surfactant concentration induces specific headgroup areal spatial variations associated with a given ripple symmetry. The study suggests a compositional route which can be exploited to control and design membranes with desired structural functionalities as well as understand the implications of these modulated phases on other biophysical processes such as pore formation, fusion and phase transitions.

* Current Address: Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany

$  Current Address: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139