Loss of gelation ability of Pluronic(R) F127 in the presence of some salts

In this investigation, we show that certain salts with multivalent anions, at characteristic concentrations, prevent Pluronic(R) F127 solutions from forming gels. This was done by measuring the gel formation (T-1), gel melting (T-2) and cloud point (T-cp) transitions of 20% Pluronic(R) F127 gels in the presence of various such salts. All the salts studied lower all three transition temperatures. The degree of lowering is proportional to salt concentration and can be ascribed to salting-out effects. Both the cation and anion appear to influence T-1, while T-2 and T-cp are predominantly influenced by the salt anion. T-1 is lowered because salts decrease the critical micelle concentration (cmc) of F127. The effect on T-2 and T-cp parallels the precipitation of poly(ethylene oxide) from aqueous solution in the presence of salts and follows the Hofmeister series. Multivalent anions reduce T-2 to a much greater extent than T-1, and this results in a loss of gel formation above a certain 'no-gel' salt concentration. Copyright (C) 1996 Elsevier Science B.V.