J. Phys. II France
Volume 3, Numéro 6, June 1993
Page(s) 903 - 926
DOI: 10.1051/jp2:1993174
J. Phys. II France 3 (1993) 903-926

Spiral textures in lyotropic liquid crystals : first order transition between normal hexagonal and lamellar gel phases

K. M. McGrath1, P. Kékicheff1 and M. Kléman2

1  Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia
2  Ldaboratoire de Physique des Solides URA 002, associé au C.N.R.S., Bâtiment 510, Université Paris-Sud Orsay, 91405 Orsay Cedex, France

(Received 2 September 1992, accepted in final form 12 February 1993)

The first order transition between the normal hexagonal phase (H $_{\alpha}$) and lamellar gel phase (L $_{\beta}$, L $_{\beta'}$, L $_{\delta}$, ... type) in lyotropic liquid crystals of binary surfactant/water systems is investigated. Structural transformations and epitaxial relations are investigated by small-angle X-ray scattering on powdered and oriented samples. By slow evaporation of water, growth of the gel layered structure from the two-dimensional packing of surfactant cylinders of the hexagonal mesophase in the presence of a solid wall reveals a spectacular new texture composed of interwoven spirals. It is demonstrated that the layers grow from the rods of the hexagonal phase, in planes coplanar with the hexagonal packing and perpendicular to the wall. The configuration is such that line wedge disclinations of strength s= + 1/2 of the hexagonal phase are preserved through the phase transition. Estimates of the radii for the developable domain and cores, and also for the bending elastic constant are obtained. A mechanism for the phase transformation is discussed in view of topological structural transformations and a modification of the short-range order associated to the disorder order transition of the configuration of the paraffinic chains.

61.30E - 61.30J - 64.70M - 68.55

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