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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 12: Polymer Physics III: Interfaces

CPP 12.5: Vortrag

Dienstag, 27. März 2007, 11:15–11:30, H40

Smectic Layering at Surfactant-laden Isotropic Liquid Crystal/Water Interfaces — •Christian Bahr — Max Planck Institute for Dynamics and Self-Organization, D-37073 Göttingen

Thermotropic liquid crystals exhibit surface-induced order at temperatures where the bulk phase is disordered. Many smectic compounds show in their isotropic phase the formation of a smectic layer at interfaces to air or solid substrates; when the isotropic – smectic-A bulk transition is approached, the ordered surface phase grows in thickness via a series of individual layering transitions. Theoretical models [1] predict complex surface phase diagrams in which the individual layer transition lines end at critical points or collapse at triple points to multiple-layer transitions.

We present here the first study of smectic layering at surfactant-laden liquid crystal/water interfaces. Variation of the surfactant concentration c_s offers an easy way to tune the strength of the ordering surface field [2]. Whereas at higher c_s-values the usual series of single-layer transitions occurs, we observe at low c_s-values layering transitions at which the thickness of the surface phase jumps by a multiple number of single smectic layers. The multiple-layer transition lines split off at triple points into single-layer transition lines. This is the first experimental observation of this type of surface triple points.

[1] Z. Pawlowska, T. J. Sluckin, and G. F. Kventsel, Phys. Rev. A 38, 5342 (1988); A. M. Somoza, L. Mederos, and D. E. Sullivan, Phys. Rev. E 52, 5017 (1995).

[2] Ch. Bahr, Phys. Rev. E 73, 030702(R) (2006).