SOME CRITICAL-POINTS IN THE INTERACTION BETWEEN HOMOGENEOUS NONIONIC SURFACTANTS AND POLY(ACRYLIC ACID)

Single hexaethylene glycol mono(n-dodecyl) ether or octaethylene glycol mono(n-dodecyl) ether in aqueous solution and their mixtures with poly(acrylic acid) (PAA) were studied by surface tension, fluorescence, dye solubilization, viscosity and pH methods. The CMC and several critical surfactant concentrations for the interaction were determined. The starting point of micellar aggregation on the PAA chain (T-1) and the point at which free micelles appeared in the solution were found and identified by the various methods. The concentration at which free surfactant molecules reappear in the system, was a transitional range rather than a critical point and was identified with certainty only by surface tension measurements. The data were discussed taking into account the interaction of both ethoxylated and hydrophobic moieties of the surfactant with PAA (i.e. hydrogen bonding and hydrophobic bonding respectively). Finally, the relationship between T-1 and the ethoxylated and hydrophobic moieties of the surfactants was considered.