Grazing incidence X-ray reflectivity of coumarin side-chain polymers used for liquid crystal photoalignment layers

• Published in: Synthetic metals 2002-03, Vol.127 (1), p.95-98
• Main Authors: Jackson, P.O., Bergmann, G., Hogg, J.H.C., O’Neill, M., Hindmarsh, P., Kelly, S.M., Clark, G.F.
• Format: Article
• Language: English
• Subjects: Applied sciences; Coumarin; Crosslinking and degradation; Exact sciences and technology; Liquid crystal; Photoalignment; Physicochemistry of polymers; Polymer; Polymers and radiations; Surface roughness; X-ray reflectivity
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/S0379-6779(01)00606-3

Specular X-ray reflectivity measurements are used to examine photoinduced surface roughness of side-chain coumarin polymers that form liquid crystal photoalignment layers. Thin films were irradiated with polarised or unpolarised ultraviolet light and the X-ray reflectivity at grazing incidence was measured for samples irradiated with different ultraviolet fluences. Kiessig fringes are observed over a large dynamic range and a comparison of the measured and calculated reflectivity gives a value for the surface roughness. The photoinduced roughness increases with ultraviolet fluence, from 5.5 to 20 Å. Negligible photoinduced roughness is detected for a film, which was previously irradiated using conditions that give strong planar liquid crystal alignment. Specular reflectivity data taken with the plane of incidence of the X-ray parallel and perpendicular to the polarisation direction of the ultraviolet light are identical within experimental uncertainty. Hence in-plane anisotropic surface roughness is not observed.