title: AFM study of defect-induced depressions of the smectic-A/air interface.
abstract: The smectic-A/air interface of liquid-crystal droplets with antagonistic boundary conditions is studied by atomic force microscopy (AFM). The droplets are prepared on coated silicon wafers on which a planar alignment is preferred in contrast to the homeotropic alignment at the air interface. As a result, focal conic defects appear in the smectic-A phase causing a characteristic pattern of depressions in the droplet surface. The dimensions of the defect-induced depressions are measured by AFM as a function of temperature for two different compounds possessing a smectic-A-isotropic and a smectic-A-nematic transition. Whereas the results are independent of temperature in the smectic-A-isotropic case, reflecting the first-order nature of the transition, a pronounced temperature dependence is observed for the second compound, where the depth of the defect-induced depressions decreases continuously with increasing temperature and vanishes at the second-order transition to the nematic phase. These observations can be qualitatively explained through the behavior of the layer compressional elastic constant at the smectic-A-nematic transition.
authors.affiliation: Max Planck Institute for Dynamics and Self-Organization, Bunsenstr. 10, D-37073 Göttingen, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Designolle
authors.forename: S
authors.initials: S
authors.lastname: Herminghaus
authors.forename: T
authors.initials: T
authors.lastname: Pfohl
authors.forename: Ch
authors.initials: Ch
authors.lastname: Bahr