Effect of additives on the micellar behaviour of aqueous alkaline earth metal dodecyl sulphates

The critical micelle concentrations (CMCs) of alkaline earth metal dodecyl sulfates have been determined in the presence of alkali metal dodecyl sulfates, cholic acid, ammonium chloride, and sodium citrate—key ingredients commonly found in various cough syrups. Two key observations emerge from the data obtained. First, the presence of these additives leads to a decrease in CMC values. Second, the efficiency of CMC reduction follows the order: sodium citrate > cholic acid > potassium dodecyl sulfate > sodium dodecyl sulfate > ammonium chloride (NH₄Cl) > lithium dodecyl sulfate. The decrease in CMC is attributed to the presence of added ions, such as sodium, which reduce electrostatic repulsion between the surfactant head groups, thereby facilitating micelle formation.