Analysis of surface and bulk properties of amphiphilic drug ibuprofen and surfactant mixture in the absence and presence of electrolyte

• Mixed micelles formed in the presence of electrolyte are more stable in comparison to its absence.
• The synergism in mixed micelle formation can be enhanced by adding salt.
• Ibuprofen form ion-pairs with the sodium counterions of the surfactant.

In the present work, the micellization, adsorption and aggregation behavior of mixed drug-surfactant systems, in the absence and presence of electrolyte (100 mM NaCl) were investigated by surface tension and fluorescence measurements. The critical micelle concentrations (cmc) of the mixtures fall between the values of the individual components, which indicate nonideal behavior of mixing of the components. On the basis of regular solution theory (RST), the micellar mole fractions of surfactant (X1) and interaction parameter in solution (β  ) were evaluated, while their interfacial mole fractions (X1σ) and interaction parameters at the interface (βσ) were calculated using Rosen's model. The results indicate that the surfactant's contribution is greater than that of the drug both at the interface and in micelles. The short and rigid hydrophobic structure of the drug resists its participation in micelle formation more than in the monolayer, leading to X1 < X1σ. Values of the surface excess (Γmax) and minimum area per head group (Amin) indicate attractive interactions. Γmax increases and Amin decreases as the surfactant mole fraction increases. The results have applicability in model drug delivery.

Schematic diagram showing ion pair interaction between SDBS micelle and IBF.Figure optionsDownload as PowerPoint slide