Evaluation of mixed micellar interactions of C_nBCl and SDBS mixtures using dissociated Margules model and influence of different salts

Abstract

The conductivity measurement has been used to determine the first and second CMC's (CMC 1 and CMC 2 ) of alkyldimethylbenzylammonium chloride (C n BCl; n = 12, 14 and 16) as well as gemini surfactant trimethylene-1,2-bis-(dodecyldimethylammonium bromide) (12-2-12) with sodium dodecylbenzenesulphonate (SDBS) in aqueous solutions using Rubingh's the regular theory approximation as well as the dissociated Margules Model. The use of Margules model allows us to calculate activity coefficients of the constituents and hence provides better values of micellar parameters for asymmetric mixed systems as compared to the regular solution theory. The CMC 1 values for C n BCl/SDBS mixtures were seen to be lower than those predicted from their ideal mixtures suggesting synergistic interactions although the synergism increases with chain length (n) of the cationic surfactant. Both CMC 1 and CMC 2 experience a decrease with rising values of n. The addition of salts including NaCl, KCl, NaBr, Na 3 PO 4 , and Na 2 SO 4 in mixtures of C 16 BCl and SDBS suggests that salt counterions have a considerable impact on CMC 1 when either surfactant is in excess. Zeta potential (ζ) measurements provide more evidence in favor of these observations. The thermodynamic features of micellization have also been scrutinized using isothermal titration calorimetry (ITC).

Water Induced Alterations in Self‐Assembly of a Bio‐Surfactant in Deep Eutectic Solvent for Enhanced Enzyme Activity

“…An increase in entropy upon aggregation generally refers to the dehydration of alkyl chain during its transfer from aqueous to micellar phase. [54] In the present case, the aqueous-DES nano-domains solvates the aggregates even after aggregation, where size and content of such nano domains decreases with increase in water content. Therefore, only the transfer of solvating aqueous-DES to bulk cannot account for the observed decrease in entropy with increasing content of water.…”

“…Apparent molar enthalpy of solvation of surfactant ion, counter-ion, dissociation of aggregates, aggregation number (N agg ), degree of counter-ion binding (β) and another set of interactions between surfactant ions and solvent governs the enthalpy change prior to aggregation whereas dilution of aggregates along with repulsive/attractive forces between aggregates dictates the enthalpy changes beyond aggregation. [51,[54][55][56] A gradual decrease in exothermic change with an increase in the concentration of SLS shows the increasing dominance of desolvation of alkyl chain of SLS (endothermic) over hydrophobic interactions between alkyl chains (exothermic) and electrostatic repulsions between ionic head groups (exothermic) prior to cac. The screening of electrostatic repulsions upon adsorption of counterions in the stern layer of the aggregates (endothermic) and the dilution of aggregates beyond cac dominate and result in endothermic DH o agg changes (Table 3) as all other factors remains constant.…”