Liquid Crystal Alignment on Surfaces with Orientational Molecular Order: A Microscopic Model Derived from Soft X-ray Absorption Spectroscopy
To investigate the microscopic origin of liquid crystal alignment on rubbed polymer surfaces several novel experimental techniques have been developed, which allow probing of the liquid crystal-polymer interface on a molecular level. The understanding of the alignment mechanism presented in this Chapter is based on the detection of the molecular orientation at rubbed polymer surfaces by surface sensitive, polarization dependent soft x-ray absorption spectroscopy resolving the near edge x-ray absorption fine structure (NEXAFS) of the absorption coefficient. NEXAFS spectroscopy is a powerful experimental technique for the investigation of ordering phenomena in thin films and at surfaces with element specificity, chemical selectivity, and sensitivity to the presence of orientational order. Its sampling depth can be tuned from the outermost surface layer only to a few ten nanometers deep into the film bulk. Also, this technique is especially powerful for the investigation of ordering phenomena in the absence of long-range order, as often the case in polymers, due to the local nature of the x-ray absorption process.
KeywordsAnisotropy Graphite Polyethylene Phenyl Polystyrene
Unable to display preview. Download preview PDF.
- 2.K. Siegbahn, ESCA; Atomic, Molecular, and Solid State Structure Studied by means of Electron Spectroscopy, Almqvist & Wiksells, Uppsala, 1967.Google Scholar
- 6.J. Stöhr, NEXAFS Spectroscopy, Springer Series in Science, Vol. 25, Heidelberg, 1992.Google Scholar
- 7.J. Sakurai, Advanced Quantum Mechanics, Addison-Wesley, London, 1967.Google Scholar
- 8.E.W. Thulstrup and J. Michl, Elementary Polarization Spectroscroscopy, VCH Publishers, Inc., New York, 1989.Google Scholar
- 9.P.G. De Gennes and J. Prost, The Physics of Liquid Crystals, Clarendon Press, Oxford, 1993.Google Scholar
- 20.S. Kobayashi and Y. Iimura, Proc. SPIE, Liquid Crystal Materials, Devices, and Applications III, edited by Ranganathan Shashidhar, 2175, 122 (1994).Google Scholar
- 22.K.-W. Lee, S. Paek, A. Lien, C. Durning, and H. Fukuro, in K.L. Mittal and K.-W. Lee, editors, Polymer Surfaces and Interfaces: Characterization, Modification and Application, VSP, The Netherlands, 1996.Google Scholar
- 35.P. Chaudhari, J. Lacey, J. Doyle, E. Galligan, S.C.A. Lien, A. Callegari, G. Hougham, N.D. Lang, P.S. Andry, R. John, K.H. Yang, M.H. Lu, C. Cai, J. Speidell, S. Purushothaman, J. Ritsko, M.G. Samant, J. Stöhr, Y. Nakagawa, Y. Katoh, Y. Saitoh, K. Sakai, H. Satoh, S. Odahara, H. Nakano, J. Nakagaki, and Y. Shiota, Nature 411, 56 (2001).ADSCrossRefGoogle Scholar