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Séminaire de Rema Krishnaswamy

Rema Krishnaswamy

Jawaharlal Nehru Centre for Advanced Scientific Research Jakkur Campus, Jakkur P.O. Bangalore-560064, Karnataka

Shear induced 3D ordering of membrane defects and buckling instabilities in Surfactant Mesh Phases

Mesh phases are formed by a one dimensional (1D) stack of perforated bilayers with liquid-like or hexagonal ordering of perforations in the bilayer plane as in the random or rhombohedral mesh phases. Known since 1960s in different classes of amphiphilic systems comprising surfactants, lipids, diblock copolymers, thermotropic liquid crystals and more recently in star branched polyphiles, their response to shear flow has hardly been addressed. This is despite their structural similarity with bilayer forming phases where shear flow can couple with thermal undulations of the bilayers to give rise to various hydrodynamic instabilities accompanied by structural transitions [1,2].
I will present our recent in-situ Rheological X-ray scattering studies on surfactant mesh phases revealing for the first time two striking consequences of shear flow on the random and ordered mesh phases :
i) A random mesh phase subjected to shear develop in-plane hexagonal ordering of pores and lock into a 3D structure to form R 3 m phase ;
ii) Shearing of R3m results in the buckling of bilayers out of the shear plane and a subsequent coexistence of two R 3 m phases with different lattice parameters.
These shear induced transitions nicely juxtaposes the consequence of shearing a stack of fluid- like and elastic perforated bilayers, correlating with the earlier investigations on the classical lamellar phase.
References :
[1] L. Porcar, W. A. Hamilton, and P. D. Butler, Langmuir 19 10779 (2003) and references therein
[2] V. Rathee, R. Krishnaswamy, A. Pal, M. Imperor, B. Pansu, V. A. Raghunathan, and A. K. Sood, Proc. Natl. Acad. Sci. USA , 110, 14849 (2013)
[3] Vikram Rathee, Pradip Kumar Bera, A. K. Sood and Rema Krishnaswamy (manuscript in preparation)