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, begin to aggregate into micelles in a solution.When salt is added to the solution, the CMC of SDS typically decreases. This is because the presence of salt ions can shield the electrostatic repulsion between the negatively charged head groups of SDS molecules, making it easier for them to aggregate into micelles. The extent to which the CMC decreases depends on the type and concentration of the salt added. Generally, the higher the salt concentration, the lower the CMC of SDS in the solution.