Thermodynamics and Micellar Behavior of Surface-Active Drugs in Aqueous Solution of Electrolytes: Surface Tension Study

The surface tension study of the surface-active drugs streptomycin sulphate and diphenhydramine hydrochloride has been carried out with three uni-univalent and three bi-univalent electrolytes viz. NaCl, KCl and RbCl (0.01 mol.kg -1 ), and MgCl 2 , CaCl 2 and SrCl 2 , (0.002 mol.kg -1 ) at temperature range of 298.15 to 313.15 K. The interfacial parameters like maximum surface excess concentration ( Γ max ), minimum area per surfactant molecule ( A min ), and surface pressure at CMC ( Π cmc ) have been explored. The results represent the stronger affinity between drug-electrolyte molecules, which lower the surface tension values. The CMC relations govern the hydrophobic and hydrophilic interactions in ternary system (water-drug-electrolyte). Further, the addition of electrolytes lowers the total number of drug molecules at the interface, correlated with increase in A min , and decrease in Γ max and Π cmc . Thermodynamics of micellization directs about the work done for micellization, and lighten the surface and bulk properties of drugs.