Ethoxylated nonionic surfactants in hydrophobic solvents: separation using membrane immobilized poly-acrylic acid

It is established in the literature that certain polyelectrolytes like poly-acrylic acid and ethoxylated nonionic surfactants form complex in aqueous solution due to hydrogen bonding between carboxyl group of PAA and ethylene oxide group of the surfactants. In the present study, pure ethoxylated surfactant solution in a hydrophobic solvent is permeated through a partially cross-linked PAA composite membrane to quantify the extent of separation of the surfactants in the heterogeneous system. In addition, the permeation properties of the PAA functionalized membrane were studied to establish certain characteristics of the membrane like porosity and thickness of PAA layer inside membrane pore as a function of pH. Role of ethylene oxide group variation in surfactant separation for the heterogeneous system was established by performing experiments with pure surfactants having same alkyl chain length but varying ethoxylate chain lengths. It was observed that the surfactants with higher number of ethylene oxide groups per molecule exhibit higher extent of separation from the hydrophobic solvents. The pH sensitivity of the PAA-surfactant complex is established by verifying its reversibility under varying pH conditions and it was used successfully for regeneration and reuse of the membrane.