In-Line and In Situ Monitoring of Ionic Surfactant Dynamics in Latex Reactors Using Conductivity Measurements and Ion-Selective Electrodes

Influence of Dodecylsulfate Adsorption on the Stability of Cerium Oxide Nanoparticle-Based Colloidal Aqueous Dispersions

In this contribution, the influence of the adsorption of dodecylsulfate, an anionic surfactant, on the stability of colloidal aqueous dispersions containing ceria (CeO₂) nanoparticles (NPs) was investigated using zetametry, UV-visible spectrophotometry, and potentiometry involving an ionic surfactant-selective electrode (ISSE). In particular, thanks to absorbance follow-ups carried out as a function of time, aqueous dispersions containing a given loading of CeO₂ NPs were found simultaneously to stabilize more quickly with time and to adopt a higher opacity and a more pronounced light-yellow color as the sodium dodecylsulfate (SDS) concentration increased. Knowing that this absorbance was attributed undoubtedly to CeO₂ NPs, the fact that the measured absorbance is lower for a higher amount of CeO₂ NPs in suspension, as revealed by a higher opacity of the studied dispersions, is somewhat counterintuitive. Besides the higher opacity of the dispersions, a shield effect of the adsorbed SDS layer toward UV-visible light may also explain this observation. The adsorption of dodecylsulfate on CeO₂ NPs was indeed demonstrated using zetametry measurements in the presence of SDS and the potentiometric method combined with an ISSE. This latter method did not only allow the accurate determination of impoverishment in freely diffusing dodecylsulfate (DS) anions resulting from DS adsorption on CeO₂ NPs but it also showed that this latter obeys a Freundlich isotherm.

Structure-activity relationship of cyclodextrin/biocidal double-tailed ammonium surfactant host-guest complexes: towards a delivery molecular mechanism?

In aqueous solution, the biocidal double-tailed cationic surfactant, di-n-decyl-dimethyl-ammonium chloride can form inclusion complexes with various cyclodextrins (alpha-CD, beta-CD, gamma-CD, HP-alpha-CD, HP-beta-CD and CM-beta-CD). A physicochemical study has been performed to investigate the association parameters of these host-guest complexes by combining the use of ammonium and chloride selective electrodes, NMR spectroscopy and molecular modeling. stoichiometries, equilibrium constants and geometries were determined by resorting to a specific algorithm. The antimicrobial activity of the encapsulated ammonium surfactant was compared with that of the free ammonium showing three different behaviors depending on the cyclodextrin. The close relationship between the complex structure and the biocidal activity is used to propose a delivery molecular mechanism.

Stepwise aggregation of dimethyl-di-n-octylammonium chloride in aqueous solutions: from dimers to vesicles

The self-aggregation of dimethyl-di-n-octylammonium chloride, in diluted aqueous solutions, was studied with various experimental and theoretical techniques: zetametry, conductimetry, dimethyl-di-n-octylammonium and chloride-selective electrodes, tensiometry, NMR spectroscopy ((1)H and DOSY), and molecular modeling (PM3 and molecular dynamic). The combination of the data obtained by these techniques led us to propose a stepwise aggregation process with increasing concentration: dimers (0.2-10 mM), bilayers (10-30 mM), and finally vesicles (>30 mM).