# Smectic Layering at the Free Surface of Liquid Crystals in the Nematic Phase: X-Ray Reflectivity

 Title: Smectic Layering at the Free Surface of Liquid Crystals in the Nematic Phase: X-Ray Reflectivity Author: Pershan, Peter S.; Braslau, A.; Weiss, A. H.; Als-Nielsen, J. Note: Order does not necessarily reflect citation order of authors. Citation: Pershan, Peter S., A. Braslau, A. H. Weiss, and J. Als-Nielsen. 1987. Smectic layering at the free surface of liquid crystals in the nematic phase: X-ray reflectivity. Physical Review A 35(11): 4800-4813. Full Text & Related Files: Pershan_Smectic.pdf (2.262Mb; PDF) Abstract: Smectic layering at the surface and smectic fluctuations in the bulk can be studied simultaneously by x-ray specular reflectivity and scattering measurements. There is a peak in the angular dependence of the specular reflectivity due to surface-induced smectic layering that penetrates into the bulk as $$exp(-z/\xi_{\parallel})$$ where $$\xi_{\parallel}$$ is one of the nematic critical correlation lengths. This is illustrated by measurements of the liquid-crystal materials octyloxycyanobiphenyl (8OCB) and butyloxybenzyl- idene octylaniline (4O.8). In both cases the critical divergence of the intensity of the peak in the specular reflectivity is weaker than $$\xi^2_{\parallel}$$, suggesting unexpected surface physics. The absolute value of the critical part of the density pair correlation function is determined by comparison to the Fresnel reflected intensity. Different geometries of the x-ray spectrometer are also discussed. Published Version: doi:10.1103/PhysRevA.35.4800 Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10357477 Downloads of this work: