Analytical Characteristics of Micelles Aggregations of Surfactant CTAB

Abstract

The conductometry, surface tensiometery and viscometry techniques were employed to evaluate these physico-chemical and thermodynamic properties. The thermodynamic parameters like free energy of micellization (∆G_m), free energy of absorption (∆G_ads), surface excess concentration (Γ) and minimum area per molecule (A) were calculated through surface tension measurements. Critical Micelle Concentration (CMC), degree of ionization (α) and degree of counter ion binding (β) were measured by conductometry technique. The results showed that the values of CMC of CTAB decreased with the increase in temperature. The value of CMC calculated through conductometry for pure CTAB was 0.98 M at 303 K, which was observed to decrease as temperature increased and got value of 0.95 M at 318 K. Moreover the addition of electrolyte LiCl into the surfactant lead to lowering of the CMC and got  value of 0.90 M at 3 M of LiCl. The addition of electrolyte was also observed to  decrease the values of CMC of CTAB, indicating significant electrostatic interactions between surfactant and electrolyte. Moreover the value of α calculated for pure cationic surfactant CTAB was 0.219, which tends to increase with the addition of electrolyte, while that of β value was observed to decrease from 0.780 to 0.206. This is due to the fact that greater charge density at micellar surface and diminishing in the aggregation number of micelle as well as an increase in the micellar ionization due to the incorporation of electrolyte LiCl.