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The effects of self-assembly on the hydrolysis kinetics of surfactants that contain ester bonds are discussed. A number of examples on how reaction rates and apparent reaction orders can be modulated by changes in the conditions, including an instance of apparent zero-order kinetics, are presented. Furthermore, it is shown that the examples on reaction kinetics display parallels and connections to important physicochemical aspects of surfactant aggregates, namely, the “reservoir function” of micelles and the fact that the headgroup region of micelles constitutes an aqueous environment largely distinct from the bulk solution. The examples presented can be used in teaching organic as well as physical chemistry. The text is written with the intention to be largely self-contained, in order to make it accessible for readers with different background experience.

Water-dispersible organosilica nanoparticles were synthesized using microemulsions and micellar solutions. Octadecyltrimethoxysilane (OTMS) was used as the silica source resulting in particles having a hydrophobic interior with the ability to host oil. The diameters of the formed particles could be varied between 60 and 200 nm, depending on the amount of added oil and OTMS. The size of the particles was determined using dynamic light scattering and transmission electron microscopy. Exchange-coupled diffusion nuclear magnetic resonance experiments were performed to study the exchange rates between the particles and the surrounding media. Triethylamine and tributylamine were used as probe molecules, and it was shown that they had longer mean residence times in the particles compared with in the bulk. Moreover, it was found that the mean residence time of the probe molecules increased significantly when the particles contained oil. The results also showed that the mean residence time of tributylamine was longer than that of triethylamine. Furthermore, by the use of UV-vis spectrophotometry, it was shown that the particles were able to take up benzophenone from water solutions.

Small unilamellar vesicles (approximately 100 nm in diameter) form spontaneously in aqueous mixtures of histidine and sodium dodecyl benzenesulfonate. By manipulating pH, a gradual transition from micelles to vesicles to bilayers to precipitate is observed. The self-assembly of vesicles occurs over a wide range of compositions when the solution pH is lower than 6.0, the pKa of the imidazole moiety on the histidine molecule. This phenomenon is likely the result of attractive interactions between the negatively charged benzenesulfonate headgroups and the positively charged imidazole group in the amino acid. Similar results are obtained when imidazole salt itself is used.