Stoichiometry of Langmuir-Blodgett Multilayers of Docosylammonium Arsenate

The stoichiometry of Langmuir-Blodgett multilayers of docosylammonium arsenate has been studied by means of neutron-activation analysis. The content of arsenic in the multilayer systems has been determined at different pH’s and concentrations of arsenate in the aqueous subsolution, and the number of anions per docosylamine molecule, 6, has been evaluated. The results show that the counterion inclusion is stoichiometric and that it is due to electrostatic interaction between the positively charged ammonium groups of the monolayer and arsenate anions of the subsolution. From the B/pH and O/Co dependences, it follows that the divalent counterions HAs0d2- are predominantly present in the multilayers.