A chemodegradable surfactant system based on oxidation of disulfide bonds using hypochlorite

We report a chemodegradable surfactant system based on oxidation of Br-N+(C H3)(3)(CH2)(8)SS(CH2)(8)N+(CH3)(3)Br- (1) to N+(CH3)(3)(CH2)(8)SO3- (2) by addition of sodium hypochlorite (NaOCl). Prior to oxidation, the interfacia l properties of aqueous solutions of 1 (critical micelle concentration simi lar to 1 mN/m and limiting surface tension similar to 45 mN/m) are similar to those of Br-N+(CH3)(3)(CH2)(16)N+(CH3)(3)Br- (3), demonstrating that int roduction of the disulfide bond into the surfactant structure does not subs tantially change its surface-active properties. The surface tensions of aqu eous solutions of 1 were found to increase by up to 26 mN/m upon addition o f NaOCl. These changes in surface tension were measured within similar to 2 -3 min of the addition of a stoichiometric ratio of NaOCl to 1 of 6:1 at 25 degrees C. The oxidation of 1 to 2 can also be effected over a wide range of pH (3 < pH < 11) and by using commercial formulations of bleach. The vol ume of bleach necessary to oxidize a 2 mM solution of 1 was less than 2.5% of the total volume of the solution. We demonstrate, in addition, that oil- in-water emulsions formed from 5 wt % dodecane in a 10 mM aqueous solution of 1 are visually stable over 24 h but can be disrupted (within similar to 10 min) upon addition of NaOCl (6:1 stoichiometric ratio of NaOCl to 1).