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.

Effect of Spironolactone on the Micellar Properties of Non-Ionic Surfactant: Assessment by Conductivity and Surface Tension Methods

An interaction of spironolactone (SPI) with octyl phenol ethoxylate (Triton-X-100 or TX-100) has been investigated by using conductometric and tensiometric measurement. The value of critical micellar concentration (CMC), degree of ionization (a) and thermodynamic parameters like standard enthalpy of micellization (?H°m), standard entropy of micellization (?S°m) and standard Gibb’s free energy (?G°m) were determined by conductivity data. The negative value of ?G°m shows spontaneity in the solubilization of drug. Various interfacial parameters such as maximum surface excess concentration (Gmax) and minimum area per molecule (Amin) was determined by surface tension measurement. All these parameters have been discussed in terms of drug-surfactant interactions. Based on the result it was found that variation in the presence of spironolactone in micellar properties of TX-100 increases with increase in concentration of drug. This study will help the pharmaceutical industries in the discovery of new drug and enhancement of their bioavailability.

The Role of Non-Ionic Surfactants in Solubilization and Delivery of Sparingly Soluble Drug Naproxen Sodium (NS): A Case Study

Nonsteroidal anti-inflammatory hydrophobic drugs (NSAIDs) are amongst the most commonly given categories of drugs worldwide in the treatment of pain, irritation and some of them even fever in many conditions. Critical micelle concentration of NSAIDs with Naproxen sodium (NS) and its mixture with non-ionic surfactants i.e. Tween 20, Tween 40 and Tween 60 was investigated at 293 K, 303 K, 313 K and 323 K at different concentrations using surface tension and dynamic laser light scattering (DLS) techniques. Due to amphiphilic behaviour in aqueous solution NS form aggregates at sufficiently high concentration. Thermodynamic/adsorption properties like free energy of micellization (ΔGmic), enthalpy of micellization (ΔHmic), entropy of micellization (ΔSmic), Γmic and area per molecule (A2) of NS in the presence of surfactants were also measured at different temperatures. The results showed that the presence of surfactants favoured the ΔGmic and become more enhanced with increase in temperature. Further the solubility of drug is more favourable with increase in polyethylene chain in basic surfactant molecules i.e. 20–60, which indicates that Tween-60 enhanced the solubility of NS more comparatively to Tween-40 and Tween-20 and may be applied as best additive for solubilisation of NS.