OPTICAL DETERMINATION OF THICKNESS OF THIN LIPID FILMS

In order to determine the thickness of thin lipid films from their reflectivity, it has previously been necessary to make assumptions concerning the refractive index variation within the film. In this communication, a method is derived for determining the thickness of films in water which is independent of such assumptions. It is shown that the reflectivity does not depend on the particular refractive index variation within the film but is, to a good approximation, determined only by the average refractive index and total thickness of the film. The theory is applied to measurements made with lecithin black films, where a value of 62 ± 2 Å is obtained for the total film thickness. © 1969 Academic Press Inc. (London) Ltd.