Double Refraction of Oriented Surface Layers

Abstract

WE have extended the scope of a method recently described¹ for the measurement of refractive indices of liquids in thin films, and have obtained evidence of the double refraction of the interfacial layer between melted normal fatty acids and glass. Acids with more than ten carbon atoms in the chain are being examined. The birefringence is small, usually less than 0.0001, and exists only over a narrow temperature range of a few degrees immediately above the solidification point of the acid. This provides optical evidence that the molecules of the fatty acids are oriented at a glass-liquid interface to a depth comparable with a wave-length of visible light². The sharpness of disappearance of the birefringence at a critical temperature is thought to indicate that the anisotropic layer is a new phase, and that the fatty acid behaves as a liquid crystal immediately above its solidification point.