Dresden 2009 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 6: Thin Films
CPP 6.9: Vortrag
Montag, 23. März 2009, 16:15–16:30, ZEU 160
Stability of smectic films in water — •Yasutaka Iwashita1, Christian Bahr1, Ralf Seemann1,2, and Stephan Herminghaus1 — 1MPI for Dynamics and Self-Organization, D-37073 Goettingen — 2Experimental Physics, Saarland University, D-66041, Saarbruecken
Free-standing smectic films in air, consisting of plane layers parallel to the film surfaces (homeotropic alignment), have been widely studied for decades [1]. In liquids like water, on the other hand, such stable films have not been observed due to the planar alignment of thermotropic liquid crystals (LCs) at the interface. However, it has been shown that LCs can align homeotropically at the interface to water with the aid of surfactants [2]. An advantage of this system is the tunable anchoring potential via the concentration of the surfactant [3].
Here we focus on smectic-A (SA) films of the cyanobiphenyl series (nCB, n = 10 and 12) in water stabilized by a surfactant, monoolein. These systems show surface smectic ordering at the LC-water interface in a range of about 2 K above the isotropic - SA transition temperature, TA [3]. First we studied smectic films separating water droplets in microfluidic channels: the foam-like structure made up by the water droplets shows a coarsening time which diverges as T → TA+. The voltage for electrocoalescence of the water droplets also increases towards TA. In addition, we demonstrate the generation of large-area (5 × 5 mm2) SA films showing layer-by-layer thinning on heating around TA.
[1] P. Pieranski et al., Physica A 194, 364 (1993).
[2] J.M. Brake et al., Langmuir 19, 6436 (2003).
[3] C. Bahr, Phys. Rev. Lett. 99, 057801 (2007).