(680c) Instability of Liquid Crystal Thin Film on Topographically Patterned Substrates

Ultrathin liquid films tend to rupture and form isolated droplets by destabilizing Van der Waals interaction on a defect free smooth solid surface. This phenomenon is termed as dewetting [1]. Dewetting is a sequential process starting from rupturing and creation of holes at different locations on the thin films. Then holes grow and coalesce with the neighbouring holes to form cellular like interconnected ribbons. Finally these ribbons disintegrated into isolated random droplets [1].Dewetting can be use as a very effective tool to fabricate different nano scale or meso scale structures of different materials like homo polymer, block co-polymer, liquid crystal etc. For example, dewetted and aligned liquid crystal droplets can be use in opto-electronic applications. Here, we have reported the dewetting mechanism of liquid crystal (5CB) thin film on flat and topographically patterned (one dimension grating) polymer substrates. We observed that the dewetting mechanism of liquid crystal thin films on topographically patterned substrates is different than its homo-polymer counterpart. Dewetting of liquid crystal thin film on topographically patterned surface is independent of surface heterogeneity. But patterned directed dewetting was obtained for homo polymer on topographically patterned substrates [2]. Different intermediate liquid crystal structures were created on spin coating platform by changing different coating parameters. We have obtained a transition concentration of liquid crystal solution for discontinuous to continuous film on flat as well as 1-D topographically grating substrates. Here, we have also reported the spin dewetting process for liquid crystal on flat as well as topographically patterned substrates. Spin dewetting is a very unique process where an ultra thin film rupture and form isolated droplets during the spin coating process itself by coating with very dilute solution and high rpm[3]. Dewetting process of liquid crystal thin films were captured under optical microscope in both bright field and polarised modes. The morphology, macroscopic physical orientation and phase transition of dewetted and spin dewetted liquid crystal droplets were also observed under polarised microscope and atomic force microscope platform.

References:

[1].Reiter,G.,Phys. Rev. Letts., 1992, 68, 75.

[2]. Roy, S., Mukherjee, R., ACS Appl.Mater. Interfaces., 2012, 4(10), 5375.

[3]. Bhandaru, N., Das, A., Salunke, N., Mukherjee, R., Nano Lett., 2014, 14(12), 7009.