AN INVESTIGATION OF INTERLAYER SPACING IN MULTILAYER ASSEMBLIES OF LANGMUIR-BLODGETT-FILMS OF MIXED FATTY-ACIDS

The systematics of the variation of the interlayer spacing of Langmuir-Blodgett (LB) films of metal salts of mixed fatty acids, A'(x)A(1-x), with the length of A' hydrocarbon chain (beheneic acid C-22) being larger than the A hydrocarbon chain (arachidic acid, C-20, or stearic acid, C-18). The c parameter shows considerable deviation from Vegard's law behavior except for the x = 0.50 composition. The results of these LB films have been analyzed for the first time in terms of recent theories on the changes in c parameter of intercalated layered compounds employing a rigidity parameter, P, for the layers. The incremental interlayer spacing on intercalation of A' species is proportional to (1 - x)(P) with P = 2 when x < 0.50 and P similar to 3 when x > 0.50 with the possibility of an ordering of the A' and A species when x = 0.5.