Viscosity, Critical Micelle Concentration and...

Viscosity, Critical Micelle Concentration and Activation Parameter for Fluidity of Sodium Decyl Sulfate (SDS) and Potassium Decyl Sulfate (PDS) in Alcoholic Systems

Author Name : Dr. Mayank

ABSTRACT

Surfactants constitute a major class of substances which are able to be absorbed at air-water interface or oil-water interfaces and also at surfaces of solids. The surface activity of these materials is due to the structural features of their molecules. When surfactant is dissolved in solvent, its hydrophobic part causes distortion of solvent fluid thus increasing the free energy of the system. Surfactants therefore concentrate at the interface while hydrophilic group (carrying a negative or positive charge) opposes this process. The solubility and relative size of polar and non polar part in relation to overall molecular structure determine the surface activity of such substances. CMC is probably the simplest method of characterizing the micellar behaviour of surface active agents (solutes).  The viscosity of Sodium decyl sulfate (SDS) and Potassium decyl sulfate (PDS) surfactants in alkanol increases with increasing surfactant concentration which may be attributed due to the increasing tendency to form aggregates with increasing concentration of surfactant. The CMC values obtained by viscosity are in close agreement with those obtained from conductance   measurements. The entropy shows a little change above the CMC but below CMC there is an appreciable linear increase. Thermodynamic parameters of the systems also calculated and compare with the theoretical values.

Key Words: Viscosity, sodium decyl sulfate, CMC, Micelles, anionic surfactants, Fluidity, alcohol-water system.