Properties of block copolymers in aqueous salt solutions

The critical micelle concentrations (c.m.c.) of four polyoxy-ethylene/polyo xypropylene/polyoxyethylene (POE/POP/POE) block-copolymers in aqueous salt solution obtained from the dye spectral method at 30 degrees C are reported . The marked decrease in c.m.c, over two orders of magnitude on the additio n of salts which lower the cloud point (CP) e.g. NaBr, NaCl and Na2SO4 is o nly shown by these polymeric surfactants. Salts which increase the CP (e.g. NaI and NaSCN) increased the c.m.c. A strong decrease in c.m.c. with incre ase in the concentration of sodium chloride (0-3.5 M) reveals that the salt induces micellization at lower concentration bit increasing hydrophobicity in POP and decreasing hydrophilicity in POE, conditions that favour micell ization.