Fabrication and characterization of heteropolyanion Langmuir-Blodgett films

The possibility of the formation of Langmuir-Blodgett (LB) films with dimet hyldioctadecylammonium (DODA) after the addition of cobalt(II)-substituted Dawson-type tungstodiphosphate anion (briefed as (H2O)(CoP2W17O618-)-P-11) in the subphase has been explored. Marked modifications of the compression isotherms are observed when this anion is dissolved in the subphase, which demonstrates that the polyanions interact with the monolayers. LB films hav e been readily obtained from this system. The adsorption Fourier transform IR (FT IR) spectroscopy, atomic force microscopy (AFM), X-ray diffraction ( XRD) and cyclic voltammetry (CV) have been used to investigate the morpholo gical and molecular structure of the deposited film. The FT IR results show ed the presence of the polyanion within the LB films, and the shift for its characteristic bands may be related to the presence of positively charged DODA. AFM measurement reveals that the LB films of DODA/(H2O)(CoP2W17O618)- P-II are regularly and uniformly deposited on the substrate. XRD experiment s prove that the lamellar structure of the LB films of DODA/(H2O)(CoP2W17O6 18-)-P-II is well-defined. The LB films of DODA/(H2O)(CoP2W17O618-)-P-II im mobilized onto an indium-oxide (ITO) glass, in aqueous solutions of pH 2.0- 5.0, show quite facile redox reactions even for multilayers. All the experi ments carried out in the present study suggest that the new materials of he teropolyanions can be formed by LB techniques and beneficial physicochemica l properties of heteropolyanions can be maintained/enhanced through molecul ar-level design. (C) 1999 Elsevier Science S.A. All rights reserved.