Photoinduced changes of surface order in coumarin side-chain polymer films used for liquid crystal photoalignment

Journal Article · Mon Aug 08 00:00:00 EDT 2005 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.2009070· OSTI ID:20702545

Bergmann, G; Jackson, P O; Hogg, J H.C.; Stirner, T; O'Neill, M; Duffy, W L; Kelly, S M; Clark, G F ^[1]

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1. Department of Physics, University of Hull, Cottingham Road, Hull, United Kingdom HU6 7RX (United Kingdom)

Specular x-ray reflectivity probes morphological changes in a crosslinkable coumarin photoalignment polymer film resulting from ultraviolet irradiation. An ordered surface layer with density oscillations compatible with planar side-chain alignment is obtained before irradiation. The ordering is enhanced in the early stages of crosslinking. This is attributed to the photoinduced increase of mobility of the side-chains resulting from the creation of free volume by the crosslinking process. The expansion of the thin film confirms that free volume is created. The surface ordering decreases with prolonged ultraviolet irradiation because of increased material viscosity resulting from a high crosslinked density. The implications of surface ordering on liquid crystal photoalignment are discussed.

• OSTI ID: 20702545
• Journal Information: Applied Physics Letters, Vol. 87, Issue 6; Other Information: DOI: 10.1063/1.2009070; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COUMARIN
CROSS-LINKING
EXPANSION
IRRADIATION
LAYERS
LIQUID CRYSTALS
MORPHOLOGICAL CHANGES
MORPHOLOGY
POLYMERS
REFLECTIVITY
THIN FILMS
ULTRAVIOLET RADIATION
VISCOSITY