Surface anchoring structure of a liquid crystal monolayer studied via dual polarisation interferometry

Tan, Osbert; Cross, Graham H

Abstract

The self-organization of liquid crystal molecules of 4-n-pentyl-4′-cyanobiphenyl (5CB) forming an oriented monolayer by condensation from the vapor phase onto a silicon oxynitride surface has been observed using the evanescent wave dual slab waveguide dual polarization mode interferometry (DPI) technique. Two distinct stages to the layer formation are observed: After the formation of a layer of molecules lying prone on the surface, further condensation begins to densify the layer and produces a gradual mutual alignment of the molecules until the fully condensed, fully aligned monolayer is reached. At this limit the full coverage 5CB monolayer on this surface and at a temperature of 25 °C, is found to be anchored with an average molecular axis polar angle of 56±1° and with a measured thickness of 16.6±0.5 Å. These results are in reasonable agreement with the molecular dimensions provided by molecular models. The apparent precision and accuracy of these results resolves some wide disparity between earlier studies of such systems. Previous difficulties in determining optogeometrical properties of such ultrathin birefringent films using ellipsometry or in the need for complex modeling of the film layer structure using x-ray reflectivity are overcome in this instance. We provide a technique for analyzing the dual polarization data from DPI such that the bulk refractive index values, when known, can be used to determine the orientation and thickness of a layer that is on the nanometer or subnanometer scale.

Citation

Tan, O., & Cross, G. H. (2009). Surface anchoring structure of a liquid crystal monolayer studied via dual polarisation interferometry. Physical review E: Statistical, nonlinear, and soft matter physics, 79(2), Article 021703. https://doi.org/10.1103/physreve.79.021703

• Journal Article Type: Article
• Publication Date: Feb 1, 2009
• Deposit Date: Oct 17, 2011
• Publicly Available Date: Oct 20, 2011
• Journal: Physical review . E, Statistical, nonlinear, and soft matter physics
• Print ISSN: 1539-3755
• Electronic ISSN: 1550-2376
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 79
• Issue: 2
• Article Number: 021703
• DOI: https://doi.org/10.1103/physreve.79.021703
• Public URL: https://durham-repository.worktribe.com/output/1549939