J. Phys. France 51, 1733-1747 (1990)
DOI: 10.1051/jphys:0199000510160173300

Hexagonal and lamellar mesophases induced by shear

C.M. Marques^{1, 2} et M. E. Cates<sup>1

1</sup>  Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, G.B.
²  Institut Charles Sadron, 67083 Strasbourg France

Abstract
The role of a shear flow in the formation of an hexagonal mesophase is investigated and the transition between the isotropic, lamellar and hexagonal phases described in a three dimensional phase diagram [τ, u, Δ] where τ is a temperature-related parameter, u a measure of the intrinsic asymmetry of the system and Δ the strength of the shear rate. At zero shear rate the microphase separation transition (M.S.T.) is dominated by fluctuations but it acquires a strong mean-field character as Δ is increased. We find a region in the phase diagram where the same isotropic phase may undergo a transition to a lamellar or an hexagonal structure according to whether is cooled or sheared. The relevance of our results for diblock copolymers and for microemulsions is discussed.

PACS
6470M - Transitions in liquid crystals.
6130C - Molecular and microscopic models and theories of liquid crystal structure.
6210 - Mechanical properties of liquids.
6125H - Macromolecular and polymer solutions; polymer melts; swelling.

Key words
elasticity of liquids -- emulsions -- fluctuations -- liquid crystal phase transformations -- liquid crystal polymers -- liquid crystals -- phase diagrams