INTERACTION OF NONIONIC BLOCK COPOLYMERIC (POLOXAMER) SURFACTANTS WITH POLY (ACRYLIC-ACID), STUDIED BY PHOTON-CORRELATION SPECTROSCOPY

The interaction between certain hydrophilic pluronic (poloxamer) surfa ctants and a poly (acrylic acid) has been investigated, Both the PPO a nd the PEO groups of the surfactants, and the -COOH groups and aliphat ic side chains of the PAA molecule, were found to be crucial in this i nteraction to form complexes. At pH 2 and with a low poloxamer:PPLA mo lar ratio, maximum interaction was observed, giving rise to large-size d complexes that were unstable but possessing bioadhesive properties. At the same pH but with higher poloxamer:PAA molar ratio, the complexe s became smaller in size and more stable and were used to prepare stab le w/o/w emulsions. A further increase in the poloxamer:PAA molar rati o or increase in the pH causes a further decrease in particle size wit h eventual nonformation of complexes. Interaction and stability studie s of the complexes were done using photon correlation spectroscopy, Th e overall interaction appears to be a combination of hydrophobic inter action and hydrogen bonding. This has given rise to a unique ratio whi ch we have called the [oxyphobic]/[oxyphilic] ratio or OOR. The intera ction was found to depend on the molar ratio between poloxamer surfact ants and PPA; the [O](total)/[-COOH] ratio; the size of the PPO hydrop hobe, and the pH of the reaction mixture, pH measurement studies of th ese mixtures also gave similar results. (C) 1996 Academic Press, Inc.