Alignment of Discotic Lyotropic Liquid Crystals at Hydrophobic and Hydrophilic Self-Assembled Monolayers

• Published in: Journal of physical chemistry. C Vol. 116; no. 23; pp. 12627 - 12635
• Main Authors: Al-Lawati, Zuhoor H, Alkhairalla, Ban, Bramble, Jonathan P, Henderson, Jim R, Bushby, Richard J, Evans, Stephen D
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 14.06.2012
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Liquid crystals; Physics; Solid surfaces and solid-solid interfaces; Structure of solids and liquids; crystallography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Adsorbed layers; Adsorption; Nematic state; Pinning; Self-assembled layers; Liquid crystals; Free energy; Surface energy; Triphenylene
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp302634r

The alignment of the lyotropic discotic liquid crystal 2,3,6,7,10,11-hexa-(1,4,7-trioxaoctyl)-triphenylene (TP6EO2M) on −CO2H and −CH3 self-assembled monolayers (SAMs) has been investigated in order to determine whether the surface free energy could be used to control anchoring in such a system. Irrespective of the SAMs used we found that the alignment tends to be with the director in the plane of the surface. To understand why the different SAM types produce the same bulk behavior we considered the adsorption of TP6EO2M from dilute solutions. In the case of −CH3 surfaces we found the first adsorbed DLC layer lies with its triphenylene core close to the hydrophobic SAM, leaving the hydrophilic chains extending from the surface. For the −CO2H surfaces the first DLC layer is believed to be edge-on again, leading to hydrophilic chains extending away from the surface. These adsorbed DLC layers give rise to planar alignment of the bulk nematic and columnar phases.