Effect of Additives on the Clouding Behavior of an Ethylene Oxide-Propylene Oxide Block Copolymer in Aqueous Solution

Phase behavior of an ethylene oxide-propylene oxide block copolymeric surfactant Pluronic L-64 (MW = 2900, % PEO = 40) in the presence of various additives was studied from cloud point (CP) and phenol index measurements. Electrolytes with different sizes and polarizabilities of anions and cations showed an increase/decrease in cloud point; the effect of salts is discussed in terms of “salting in” and “salting out” and follows the Hofmeister series. The effect of various nonelectrolytes, viz., hydroxy compounds and amides, on the CP of L-64 was examined and discussed in terms of their influence on water structure. Ionic surfactant, viz., sodium dodecyl sulfate (SDS), increased the CP of L-64 which could be decreased drastically in the presence of small amounts of electrolytes. The clouding behavior of a mixed L-64 + SDS system in the absence/presence of salt is discussed primarily in terms of electrical charge on the micelle surface. The polyelectrolyte-like nature of the L- 64 + SDS complex is shown from viscosity measurements.