Study of the orientation of nematic thin films by the method of IR multiple frustrated total-internal-reflection spectroscopy

This paper gives estimates of the dichroic ratioof the main IR absorption bands in the multiple frustrated-total-internal-reflection spectra and the order parameter S of thin films of a nematic liquid crystal (LC) based on cyanobiphenyls (CBs). For planar-oriented CB molecules on an amorphous hydrogenated-carbon (a-C:H) surface, the value of S lies in the interval 0.63-0.68, while the dichroic ratio of the main absorption bands lies within the limits 4.3-5.3. When the CB films obtained on the surface of a plasma-polymerized layer have a homeotropic structure, S = 0.43-0.45. The change of these quantities after storage of the LC cells and as a result of heating the oriented structure to the nematic-->isotrope transition temperature is studied. The nature of the observed changes is discussed. (C) 1998 The Optical Society of America.