The effect of polyoxypropylene chain length on the critical micelle concentration of propylene oxide—ethylene oxide block copolymers

Abstract

“RPE” block copolymer surfactants obtained by the addition of ethylene oxide to n-hexyl and n-heptyl ethers of mono- to tetrapropylene glycol are described. The critical micelle concentration of the copolymers in aqueous solution were determined by surface tension and dye absorption method. A linear decrease of log [CMC] vs number of propylene oxide units in copolymer molecule was observed. The change of work of cohesion per oxypropylene group when it passes from molecular into micellar state, calculated from the Shinoda equation ( Shinoda, K., Nakagawa, T., Tamamushi, B., and Isemura, T., “Colloidal Surfactants.” Academic Press, 1963), was 0.43 and 0.42 kT for n-hexyl and n-heptyl derivatives, respectively.