Thermodynamics of the Solubilization of Water-Insoluble Dyes by Complexes of Cationic Surfactants with Poly(vinyl sulfate) of Different Charge Densities

The solubilization of two water-insoluble dyes, o-(2-amino-1-naphthylazo)toluene (OY) and 1-pyrenecalbaldehyde (PyA), by complexes of anionic polyelectrolyte and alkyltrimethylammonium bromide (C12TAB, C14TAB, C16TAB) was examined using sodium poly(vinyl sulfate) (PVS) with different charge densities at 298.2 K. The change in the Gibbs function was estimated for this solubilization equilibrium. These complexes showed a larger solubilizing capacity for OY than for PyA. Their capacity for OY was larger than that of the corresponding surfactant micelles. The charge density of PVS influenced the solubilizing capacity in C12TAB and C14TAB solutions but had little effect in C16TAB solutions. PVS with a 40% charge density had the lowest solubilizing capacity. Bound short-chain surfactants are expected to have a smaller lateral interaction with neighboring surfactants bound to PVS with a lower charge density, thus forming a less hydrophobic complex with a lower solubilization capacity. The observed weak solubilization by PVS with a low charge density was ascribed to this less hydrophobic complex.