Green Colloid Chemistry: Characterization of Environmentally Friendly Nonionic Surfactant Systems
Abstract: Phase diagrams of mixed alkylglucoside surfactants, n-nonyl-b-D-glucopyranoside and n-decyl-b-D-glucopyranoside (C9G1 and C10G1) have been examined for the purpose of determining the microstructure surrounding a closed-loop miscibiliyt gap. There are large deuterium isotope effects on the phase diagram. NMR-self diffusion, cryoTEM and TRFQ experiments show the presence of long interconnect networks of rod-like micelles throughout the micellar region, down to quite low concentrations. These networks are present throughout the micellar regions of the ternary C9G1/C10G1/H2O system. However, scale models indicate that the networks in the C9G1 rich region have scissions, whereas those in the C10G1 don't. This likely accounts for the difference in the phase diagrams of C9G1/H2O and C10G1/H2O. Titration studies were also done to investigate the pKa of a fatty acid probe at the interface of a variety of sugar-based surfactants, C9G1, C10G2, C12G2, C12G3. The average pKa observed for all surfactants and concnetrations investigated was 6.3, indicating that alkylglucoside headgroups are better hydrated than ethylene oxide surfactants, are completely nonionic, and as a result should provide a better pKa(0) reference for calculation of the electric potential at interfaces.. Finally, investigations into the influence of nonionic surfactants on dephosphorylation reactions were conducted, as well as the influence of ethylene oxide and alkylglucoside surfactants on nucleophilic substitution reactions. Results indicate that reactions conducted in the palisade layer of micelles are quite different from reactions in solvent with similar "effective dielectric constants"as the palisade layer, due to the difference in hydration. For nucleophilic substitution reactions, surfactant- substrate ethers are found to be the intermediate product in the reaction.
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