LAUSR

Interaction of carboxylic acid headgroups of arachidic acid (AA) monolayers with trivalent ions Fe3+ and La3+ is studied by using vibrational sum-frequency generation (VSFG) spectroscopy. Comparing SFG spectra of AA Langmuir monolayers on 1013M LaCl3 solutions and 1013M FeCl3 solutions with various pH values, we show that, the cation La3+ binds to carboxylic groups by Coulombic interaction as the AA monolayers deprotonate at high pH (pH 2 7). On the other hand, insoluble Fe(OH)3 complexes in the FeCl3 solution bind to the carboxylic headgroups of AA molecules enhances the ordering structure of AA monolayers as well as that of the OH network at the interfacial layers. [doi:10.2320/matertrans.MD201708]