Interaction between poly(acrylic acid) and an ethoxylated nonionic surfactant

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