Interaction between Poly(acrylic acid) and an Ethoxylated Nonionic Surfactant

The interaction between uncharged polymer and nonionic surfactants is usually weak or nonexistent, except for the association between polyacids and ethoxylated nonionic surfactants. In this paper we have studied the interaction between poly(acrylic acid) and an ethoxylated nonyl phenol ether. Below pH 3 an insoluble complex forms, which redissolves on addition of excess surfactant. While the amount of surfactant required to form the maximum amount of precipitate or redissolve the complex is linearly dependent on polymer concentration, that required for the onset of precipitation is not. Despite the polydisperse nature of the ethoxylate chain, little fractionation of the surfactant after precipitation was observed. The nonionic surfactant was preferentially partitioned into water rather than dodecane, except where the polymer/surfactant complex formed; in this case the complex dissolved mainly in the dodecane, forming a gel containing the oil. The origins of the effect of solution conditions and polymer characteristics on complex formation are discussed.