Effect of different additives on the cloud point of a polyethylene oxide‐polypropylene oxide‐polyethylene oxide block copolymer in aqueous solution

Abstract

AbstractCloud point studies on aqueous solutions of a polyethylene oxide (PEO)‐polypropylene oxide‐PEO triblock copolymer (Pluronic® L64: EO13PO30EO13, total m.w.=2900, PEO=40%; EO=ethylene oxide; PO=propylene oxide) in the presence of different additives show some interesting features. The effect of various inorganic salts was an increase or decrease in cloud point based on their salting in and salting out action and followed the Hofmeister lyotropic series. Nonelectrolytes and hydrotropes increased the cloud point by influencing water structure. Hydrotropes altered the cloud point of the copolymer at much lower concentrations than inorganic salts. Ionic surfactants produced a marked increase in the cloud point of copolymer solutions. The effect was greater for surfactants with greater hydrophobicity. Alcohols and other organic liquid additives that are infinitely miscible with water increase the cloud point of the copolymer, whereas additives that are partially miscible in water decrease the cloud point.