New Concepts of Colloid Chemistry: Nano-Adsorbent as a Solvent Component and Adsorption Protomicelle

Large molecules of dyes or other substances can act as nano-adsorbents in aqueous surfactant solutions and, being coated with surfactant molecules, they resemble surfactant micelles with a solubilizate. These micelle-like particles were called protomicelles (or, more precisely, adsorption protomicelles, as in this paper). Their formation does not require a critical micelle concentration (CMC) and begins immediately when a surfactant is added to a solution. In this spectrophotometric study of Nile red (NR) in aqueous solutions of nonanoic acid (NOA), the first case where protomicelles were more important than micelles was demonstrated. It was shown that NR solubilization in both premicellar and micellar solutions proceeds through protomicelles rather than through NOA micelles. In the theoretical part of the paper, on the basis of the chemical potential of the nano-adsorbent, it was proved that the addition of a surfactant to a solution always increases the solubility of the nano-adsorbent. The dependence of adsorption on the curvature of the nano-adsorbent surface was considered, and it was shown that the adsorption equations for flat surfaces are applicable to curved surfaces with high accuracy.