J. Phys. II France
Volume 1, Numéro 10, October 1991
Page(s) 1233 - 1252
DOI: 10.1051/jp2:1991130
J. Phys. II France 1 (1991) 1233-1252

Oily streaks and focal conic domains in L $_\alpha$ lyotropic liquid crystals

P. Boltenhagen, O. Lavrentovich and M. Kleman

Laboratoire de Physique des Solides (associé au CNRS), Bât. 510, Université de Paris-Sud, 91405 Orsay Cedex, France

(Received 11 April 1991, accepted 17 July 1991)

Observations with the polarizing microscope of defects in the lyotropic ${\rm L}_\alpha$(SmA) phase of the quasi-ternary system cetylpiridinium chloride/hexanol/brine give evidence that oily streaks are chains of focal conic domains. The chains are stable in the vicinity of the ${\rm L}_\alpha$- ${\rm L}_3$ phase transition. Such a model of oily streaks was suggested long ago by G. Friedel but its existence was not confirmed unquestionably. We discuss the geometrical, topological and energetic properties of these structures and show that their stability depends on material constants, in particular, the saddle-splay rigidity $\bar{K}$, whose value can be estimated from the parameters of the oily streaks.

© Les Editions de Physique 1991