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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: POSTER: Biological Systems + New Materials

CPP 20.18: Poster

Mittwoch, 28. März 2007, 16:00–18:30, Poster B

AFM Studies of Defect-induced Surface Modulations in Smectic Liquid Crystals — •Wei Guo and Christian Bahr — Max Planck Institute for Dynamics and Self-Organization, D-37073 Göttingen

Smectic-A liquid crystals show a common defect structure, focal conic defects, which consist of a complex arrangement of curved equidistant molecular smectic layers. In thin smectic films between a substrate and an air interface, focal conics cause depressions at the air interface which can be imaged by AFM microscopy [1].

We present here an AFM study of the defect-induced surface modulations in smectic films on various substrates and at various phase transitions. Whereas substrates causing a random planar alignment (the liquid-crystal director is oriented parallel to the substrate surface but there is no preferred in-plane orientation) lead to a pattern of circular surface depressions, we observe for substrates with an unidirectional planar alignment (the director possesses one or more preferred in-plane orientations) linear groove-like surface modulations of the air interface. In thicker films on these substrates, a complex structure is observed, in which the grooves seem to be decorated by rows of interdigitating circular focal conics.

We study also the behavior of the surface modulations at different liquid-crystal phase transitions like smectic-A – nematic, smectic-A – isotropic, or smectic-A – smectic-C.

[1] V. Designolle, S. Herminghaus, T. Pfohl, and Ch. Bahr, Langmuir 22, 363 (2006).