(775f) 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