Effect of solvents and temperature on the critical micellar concentration of sodium dodecyl sulfate and cetylpyridinium chloride

The critical micellar concentrations (cmc) of sodium dodecyl sulfate (SDS) and cetylpyridinium chloride (CPC) in acetonitrilewater media of various compositions have been determined at different temperatures. The cmc of SDS slightly decreases with the increase in acetonitrile concentration and with the increase in temperature, whereas th^t of CPC increases with the increase in concentration of acetonitrile and temperature. An attempt has been made to explain this type of behaviour. Contrary to the general expectation, the micellization of SDS and CPC in mixed solvents seems to be enthalpy-controlled rather than entropy-controlled.