MONOLAYER PROPERTY OF TRIOCTADECYLTIN CHLORIDE AT AN AIR-WATER-INTERFACE

The monolayer property of trioctadecyltin chloride has been studied by the surface pressure-area (pi-A) isotherm measurement and fluorescence microscopy. Apparent molecular areas estimated from pi-A isotherms and the morphology of the monolayers change markedly with the pH and NaCl concentration of the subphase. A homogeneous monolayer and an aggregate of three-dimensional islands are formed on the highly basic (pH > 10) and acidic (pH 2) subphases, respectively, and these structures are almost independent of the NaCl concentration. At the intermediate pH, on the other hand, the monolayer structure depends on the NaCl concentration; the homogeneous monolayer is formed on the NaCl-free subphase and the aggregate of three-dimensional islands on the aqueous NaCl subphase. These changes of monolayer structures can be interpretated in terms of the transformation of the head group between the less hydrophilic chlorinated form and the highly hydrophilic hydrolyzed (hydroxylated) form. The homogeneous monolayer can be built up on a substrate as a Y-type Langmuir-Blodgett (LB) film with a transfer ratio of unity. The present results show that organotin chlorides with long alkyl chains are novel monolayer-forming compounds though the monolayer structure is sensitive to the subphase condition.