MONOLAYERS AND MULTILAYERS OF URANYL ARACHIDATE .1. STUDY OF THE INTERACTION OF DISSOLVED URANYL IONS WITH ARACHIDIC ACID LANGMUIR MONOLAYERS

Langmuir monolayers of arachidic acid have been prepared on a subphase containing uranyl ions (O=U=O)(2+). The interaction between the urany l ions and the monolayer of arachidic acid has been studied by means o f surface pressure and surface potential isotherms and Brewster angle microscopy at different pH values (ranging from 1.5 to 8). A similar s ystematic study has been carried out in the presence of Cd2+ ions for comparison purposes. The surface pressure and surface potential isothe rms demonstrate that the acid to salt conversion of arachidic acid in the presence of uranyl ions occurs at lower bulk pH values (pH = 3.5) as compared with other bivalent metal counterions such as Cd2+. Change s in the surface morphology of the monolayer induced by the interactio n with uranyl- and cadmium ions are analyzed and the correlation betwe en the surface potential change and the morphology of the films is dis cussed.