The critical micelle concentration CMC of sodium dodecyl sulfate SDS in water at 25C is approximately 8.2 mM millimolar . The CMC is the concentration at which surfactant molecules, like SDS, start to aggregate and form micelles in a solution.The pH of the solution can affect the CMC of SDS, but the effect is generally minor. SDS is an anionic surfactant, meaning it has a negatively charged head group. At very low pH values highly acidic conditions , the negative charge on the head group can be neutralized, which may lead to a slight increase in the CMC. However, under most typical conditions pH 5-9 , the pH has a negligible effect on the CMC of SDS.