Oily streaks and focal conic domains in L lyotropic liquid crystals

(Received 11 April 1991, accepted 17 July 1991)

Abstract
Observations with the polarizing microscope of defects in the lyotropic (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 - 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 , whose value can be estimated from the parameters of the oily streaks.