Influences of NaCl and Na2SO4 on the Micellization Behavior of the Mixture of Cetylpyridinium Chloride + Polyvinyl Pyrrolidone at Several Temperatures

Herein, the conductivity measurement technique is used to determine the interactions that may occur between polyvinyl pyrrolidone (PVP) polymer and cetylpyridinium chloride (CPC) surfactant in the presence of NaCl and Na2SO4 of fixed concentration at variable temperatures (298.15–323.15 K) with an interval of 5 K. In the absence or presence of salts, we observed three critical micelle concentrations (CMC) for the CPC + PVP mixture. In all situations, CMC1 values of CPC + PVP system were found to be higher in water than in attendance of salts (NaCl and Na2SO4). Temperature and additives have the tendency to affect counterion binding values. Various physico-chemical parameters were analyzed and demonstrated smoothly, including free energy (ΔG0m), enthalpy (ΔH0m) and entropy change (ΔS0m). The micellization process is achieved to be spontaneous based on the obtained negative ΔG0m values. The linearity of the ΔHmo and ΔSmo values is excellent. The intrinsic enthalpy gain (ΔH0*m) and compensation temperature (Tc) were calculated and discussed with logical points. Interactions of polymer hydrophobic chains or the polymer + surfactant associated with amphiphilic surface-active drugs can employ a strong impact on the behavior of the gels.

Temperature Dependence of Micellization Properties of Binary Mixtures of Sodium Decylsulphate with Sodium Dodecylsulphate in Water

Conductance measurement method has been used to determine the critical micelle concentration (CMC) and counterion binding constant values of binary mixtures of sodium decylsulphate (SDeS) with sodium dodecylsulphate (SDS) in water at four different temperatures ranging from 298 K to 313 K at 5 K intervals. Rubingh′s model has been used to calculate the mixed micellization properties viz. mixed micelle composition, activity coefficient of the components, and mutual interaction parameter between the components. Variation of these mixed micellization properties with temperature has been studied. The studied binary surfactant mixtures show attractive interaction between the components and it decreases with increase in temperature, which is an interesting trend. Thermodynamic parameters of mixed micellization have also been calculated. The enthalpy (ΔH°mic) and entropy (ΔS°mic) of micellization compensate each other.

On the Thermodynamics of Micellizationof Oppositely Charged Surfactants in the Presence of Organic Additives in the Aqueous Medium

To investigate the effect of additives urea and thiourea, on the micellization behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), detailed conductance measurements were carried out in aqueous media at different temperatures. The critical micelle concentration (CMC), determined from the discontinuity in the plots of molar conductance versus square root of concentration, indicated an inhibitory effect of urea and thiourea on micelle forming ability of the surfactants SDS and CTAB in the range of composition studied. The demicellizing effect of urea has been found to be more pronounced in SDS than CTAB. These observations are further augmented by the evaluation of thermodynamic parameters of micellization. A negative change in enthalpy of micellization ($\Delta{\text{H}}_{\text{m}}^{\circ}$) indicates a strong interaction between water and the additives and a positive change observed in entropy of micellization ($\Delta{\text{S}}_{\text{m}}^{\circ}$) manifest, that the micellization is an entropy-driven process. Further $\Delta{\text{H}}_{\text{m}}^{\circ}$ and $\Delta{\text{S}}_{\text{m}}^{\circ}$ change in mutually compensating manner, so that $\Delta{\text{G}}_{\text{m}}^{\circ} < 0$ is not significantly affected. Finally, the counterion binding values (β) obtained for SDS and CTAB remain practically constant from 0.6 to 0.8 between 25 °C and 45 °C indicate that the size and shape of micelle remain essentially constant. Moreover, the increase in $\Delta{\text{G}}_{{\text{II}}}^{\circ}$ values, which represent the effect of co-solvent or additive on micellization, substantiates the above observations. Many early works has investigated the micellization behavior of surfactants using a fixed additive composition. However, in this study, variable aqueous compositions of urea (0.30–1.78 wt%) and thiourea (0.24–1.41 wt%) have been considered.