Alcohol Chain Length and Mole Fraction Dependence of the Stability of Tetrakis(cumylphenoxy)phthalocyanine and Alcohol Langmuir Films

While it has been known for about 10 years that octadecanol stabilizes Langmuir-Blodgett films of copper tetrakis(cumylphenoxy)phthalocyanine films, the mechanism for this stabilization is not fully understood. To understand more completely the molecular interactions responsible for making octadecanol a good transfer promoter, we studied mixed films- isotherms of tetrakis(cumylphenoxy)phthalocyanine and various saturated alcohols ranging in length from 13 to 24 carbons. By varying mole fraction and alcohol chain length in the various mixed films, a model of interaction was deduced based on pressure-versus-area isotherms obtained from a Langmuir trough. In this model, the aliphatic chains of the alcohols act as a stabilizing, hydrophobic support around phthalocyanine mounds of a preferred stack height. As film pressure increases, the mounds are forced above the alcohol sea, removing favorable ether-water interactions. Depending on chain length, a single or double collapse is observed, suggesting an adjustable physical barrier to forcing the stacks above the alcohols.