Conductometric Approach to the Thermodynamic of Micellization of Anionic Surfactants in the Presence of Procaine Hydrochloride

This study underscores the teleology of micellization behaviours of sodium dodecyl sulphate (SDS) and sodium lauroyl sarcosinate (SLS), an anionic surfactant. The configuration of SDS/SLS water soluble in the presence of 4.0 x 10-5 moldm-3 aqueous solution of procaine hydrochloride within the temperature range of 293.15 K to 313.15 K was observed. Critical micelle concentration (CMC), and degree of counter ion binding (β) were determined from conductivity data. The CMC of SDS and SLS decreased to reach a minimum (T= 308.15 K and 303.15 K for SDS and SLS) and then increased with increasing temperature. On applying mass action model, the obtained CMC values were used to determine the thermodynamic parameters (i.e. free energy of micellization (ΔG°m), enthalpy of micellization (ΔH°m) and entropy of micellization (ΔS°m)). As a function of temperature, the  value was negative and the negativity was enhanced in surfactants-PHC medium as compared with aqueous medium.  This is an indication that spontaneity increases in micelle formation in the SDS+PHC and SLS+PHC systems than water. Entropy-enthalpy compensation were observed on applying Lumry-Rajender-entropy compensation model. The observed compensation temperatures, Tc, for SDS and SLS, were not the same with and without PHC. SDS had Tc values of 302.8±3.14 and 307.7±1.63, while for SLS, Tc=305.46±3.14 and 307.33±2.18.  A clear indication of enthalpy–entropy compensation phenomenon was observed.