2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

Molecular Orientation of Nematic Liquid Crystals in Thin Film Coating Process

K. Song, H. Ko
Kyung Hee University, KR

liquid crystal, orientation, coating, shear

Although spin coating is the most popular method used to form a polymeric thin film for various electronic devices, its use is very limited for applications in large area sample. We formed thin liquid crystal(LC) films using a bar coating method and studied LC orientation changes in the film prepared by this coating method. In this study, photo-curable liquid crystalline di-acrylate (BASF LC242) which shows a nematic mesophase between 80 and 120°C was used. This nematic LC was bar-coated at various temperatures and then cured to thin film using UV exposure. Orientation of LC molecules in the film was investigated using polarized FTIR spectroscopy and a birefringence measurement. We found that LC molecules in the film are oriented in normal direction to the bar coating direction when coated near crystallization temperature while oriented along the coating direction with increasing coating temperature. It is known for liquid crystal polymers that LC flows show various shear induced orientation mode, i.e., the LC director tumbling (rotational) at low shear rate, wagging (oscillatory) at intermediate shear rates, and alingning (stationary) modes at high shear rates. To understand such effects in the thin film coating process of nematic liquid crystals, we investigated effects of bar coating conditions, such as coating speed, thickness, and temperature, on the LC molecular orientation in the cured film.

Nanotech 2008 Conference Program Abstract