For phase-separated multicomponent polymeric systems, characterization of the interface between the components is particularly challenging. We have observed an optical effect in the infrared that can be used to image the interface specifically. This method yields images of the interfaces based on the interfaces showing apparent absorption arising from changes in refractive index at frequencies far from the specific frequencies associated with the components of the mixture. This method has been applied to multicomponent samples of polymer-dispersed liquid crystals where the nature of the interface can be specifically altered by the application of an electric potential across the sample. Effects of this optical phenomenon on spectra from such multicomponent systems are discussed, and factors that complicate quantitative analysis of data from interfacial regions have been pointed out.
Rohit Bhargava, Shi-Qing Wang, and Jack L. Koenig, "FT-IR Imaging of the Interface in Multicomponent Systems Using Optical Effects Induced by Differences in Refractive Index," Appl. Spectrosc. 52, 323-328 (1998)