VARIATION OF MONOLAYER BEHAVIOR AND MOLECULAR PACKING IN ZINC ARACHIDATE LB FILMS WITH SUBPHASE PH

Monolayer characteristics and multilayer LB films of zinc arachidate ( ZnA) have been studied as a function of subphase pH in the range 4.9-8 .0. The monolayer stability was found to be strongly dependent on the subphase pH. Measurement of bilayer spacings in transferred multilayer s using X-ray diffraction revealed that depending on subphase pH, thre e types of molecular packing arrangements corresponding to alkyl chain tilt angles of 0 degrees, 19 degrees and 31 degrees are possible in Z nA multilayers. In certain ranges of subphase pH, more than one type o f packing arrangements were found to coexist. These results suggest th at the packing arrangement in ZnA multilayers is significantly affecte d by the properties of the monolayer at the air-water interface and ma y not be simply related to metal ion electronegativity. (C) 1998 Elsev ier Science S.A. All rights reserved.