On the Theory of Phthalocyanine Monomerization in Aqueous Surfactant Solutions

A thermodynamic theory has been formulated to substantiate a number of new phenomena experimentally revealed in the colloid science of surfactants. A description has been given for the formation of particular micelles via surfactant adsorption on their cores, the role of which is played by monomers and dimers of phthalocyanines. This gives rise to the formation of surfactant micelles and protomicelles containing solubilized monomers and dimers. The gradual formation of the (proto)micelles (coverage of the core surface with surfactant molecules or ions) upon the addition of a surfactant to a system is completed before the critical micelle concentration of the surfactant is reached. In terms of the chemical potentials and concentrations, equations have been derived to describe the influence of surfactants on the state of the monomers and dimers of phthalocyanines in aqueous solutions. It has been found that the concentrations of both particles grow with surfactant concentration. Alterations in the distribution of dimers over their structural forms with variations in surfactant concentration have been analyzed. It has been shown that, as surfactant content in a solution increases, the distribution of dimers shifts toward labile structures with the inevitable disintegration of phthalocyanine dimers into monomers. An equation has been derived to determine a new physical parameter, monomerization concentration , which corresponds to the passage from the dimeric state (inherent in phthalocyanines in pure water or dilute surfactant solutions) to the monomeric state in surfactant solutions. Equations have been presented for the chemical potentials of micelles (containing solubilized phthalocyanine monomers) and protomicelles (containing solubilized dimers). The latter actually disappear when the surfactant concentration rises approaching the critical micelle concentration.