Double cloud point of ethylene oxide–propylene oxide triblock copolymer in an aqueous solution

Anomalous double cloud point of ethylene oxide–propylene oxide triblock copolymer L62 in an aqueous solution is usually ascribed to impurities in the polymeric nonionic surfactant. In this article, the partial phase diagrams of block copolymers L62, L61, and L92 (including their mixtures) in aqueous solutions with and without the presence of 1-butanol have been determined, which indicates that double cloud point is not a peculiar character of L62 in an aqueous solution. Based on a further analysis of phenol solubilization in clear L62 aqueous solutions, a schematic phase diagram of polymeric nonionic surfactants in an aqueous solution is proposed. The schematic phase diagram was supported not only by our experimental results but also in line with the reported results in the literature.