Competitive micellization and host-guest complexation of sodium dodecyl sulfate with β-cyclodextrin: Insights from the Hofmeister series.

β-cyclodextrin (β-CD) is a macromolecule belonging to the class of cyclic oligosaccharides and is employed across diverse fields including the pharmaceuticals, food, and cosmetics, environment and agrochemical industries. This study examined the competitive interplay between micellization and host-guest complexation between the anionic surfactant sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD). The effect of sodium-based electrolytes and temperature was thoroughly investigated within the SDS@β-CD mixed system. FTIR and SEM analyses indicates the creation of a host-guest inclusion complex, with β-CD acting as the host and SDS as the guest. Conductometric analysis revealed that the β-CD greatly inhibits the micellization of the SDS, resulting in an increased critical micelle concentration (CMC) in water environment, while presence of sodium salts (NaBr/ NaSO/ NaPO/ NaOAc (sodium acetate)) counteract this inhibition, promoting micellization and lowering the CMC. This salt effect is consistent with the Hofmeister series of ions based on the hydrophobic interactions within SDS@β-CD system and is influenced by the temperature. The magnitude of thermodynamic parameters (∆G, ∆H, ∆S) indicates a spontaneous micellization process, which is driven by only entropic contributions at lower temperatures as well as joint contributions from enthalpy and entropy at higher temperatures. The findings of this study provide valuable insights into how cyclodextrins (CDs) and electrolytes can be used to fine-tune surfactant self-assembly, with implications for designing responsive systems in drug delivery, materials science, and industrial formulations.