Controlling the Dewetting of Liquid Crystals Using Two-Component Self-Assembled Monolayers

We have developed new liquid crystal (LC) alignment layers that promote homeotropic LC anchoring and exhibit a low contact angle of the nematic LC phase. These experiments were motivated by the requirements of LC-based biosensors, where thin LC layers are in contact with aqueous solution. In these systems, the LC layer is prone to de-wetting because of the relatively high LC contact angle on a standard homeotropic alignment layer composed of an octadecyltriethoxysilane (C18) self-assembled monolayer (SAM). In contrast, SAMs of ethyltriethoxysilane (C2) exhibit a low LC contact angle, but promote planar anchoring. Therefore, we prepared two-component SAMs of C18 and C2 in different proportions. We characterized our surface using three techniques: LC anchoring/birefringence, contact angle goniometry, and ellipsometry. A two-component mixed SAM, comprised of ~10% C18 and 90% C2, successfully reduced the LC contact angle by over 50% while maintaining homeotropic alignment of the liquid crystal.