Effect of the surfactant head group length on the interactions between polyethylene glycol monononylphenyl ethers and poly(acrylic acid)

The behavior of homogeneous and polydisperse ethoxylated nonylphenols in the presence of poly(acrylic acid) (PAA) was investigated by fluorescence, surface tension, viscometric and pH measurements. Critical micelle concentration (CMC), critical aggregation concentration (CAC or T-1) and various other critical points of interaction such as the appearance of free surfactant molecules at the air/water interface (T-2') and of micelles into solution (T-2) were determined. For polydisperse surfactants, the surface excess, areas per molecule and the composition of polymer-surfactant complexes were also established. T-1 was lower than CMC and was not influenced significantly by the length and dispersity of the poly(ethylene oxide) (PEO)chain. For the polydisperse surfactants, T-2' and T-2 decrease with increasing PEO chain length. The PAA practically does not affect the area per molecule, irrespective of the ethoxylation degree. The results suggest that complexes originate from hydrogen bonding and are further stabilized by hydrophobic interactions of the surfactant tails. (C) 1999 Elsevier Science B.V. All rights reserved.