Alignment of nematic liquid crystals at inorganic salt–liquid crystal interfaces

Abstract

This paper reports the results of a systematic investigation of factors that determine the alignment of nematic liquid crystals (NLCs) on inorganic salt decorated surfaces used in NLC-based gas sensors. When surfaces functionalised with different self-assembled monolayers (SAMs) possessing a variety of terminal groups are treated with coordinating metal salts, the resultant homeotropic alignment (i.e. alignment perpendicular to the surface) of NLC on these surfaces remains stable for an extended time and is independent of the functional group on the SAM. Liquid crystal alignment studies on surfaces treated with different metal ions reveal that the forces originating from coordination and non-coordination interactions are involved in promoting the homeotropic alignment of NLCs in these systems. The homeotropic alignment in these systems is unaffected by the presence of water. These results combined together, suggest that with a precise control of the alignment of NLC at the metal–NLC interfaces, these interfaces can form a robust and stable gas sensor platform.

Keywords:

• nematic liquid crystals
• homeotropic alignment
• sensors
• electrical double layer
• inorganic salts
• metal perchlorates

Acknowledgements

This research was partially supported by a Department of Defence contract. The authors would like to thank Professor Nick Abbott, Department of Chemical and Biological Engineering, University of Wisconsin, Madison, Darrin Most and Carla Volkmann for stimulating discussions and suggestions.