INFLUENCE OF SUBPHASE CONDITIONS ON THE PROPERTIES OF LANGMUIR-BLODGETT-FILMS FROM SUBSTITUTED PHTHALOCYANINATO-POLYSILOXANES

The influence of aqueous subphase conditions (ionic strength, pH, organic impurities and temperature) on the properties of monolayers from unsymmetrically substituted phthalocyaninato-polysiloxane (PCPS) and transfer of these films onto various substrates by the Langmuir-Blodgett technique are investigated. The shape of the pressure-area isotherms is independent of ionic strength but notably affected by the pH value, water-soluble organic impurities and the temperature of the subphase. Film transfer depends on the mode of the first step (dipping or lifting) and on the hydrophilicity of the substrate. A high positive surface potential for compressed monolayers of PCPS at the air-water interface is observed. The shape of the surface potential-area diagrams and the maximum value of the surface potential depend on temperature and pH value of the subphase. These data give evidence for an interaction between the PCPS molecules and the aqueous subphase the nature of which is discussed in terms of polarization of the central aromatic core, proton exchange equilibria between subphase and monolayer and redox activity of the phthalocyanine moieties. This interaction leads to a slight deformation of the radial side-chain distribution in the polymer molecule at the interface and contributes to the high stability of these unconventional monolayers. © 1990.