Details

Autor(en) / Beteiligte

• Whiddon, Christy Rondelle

Titel

Green colloid chemistry: Characterization of environmentally friendly nonionic surfactant systems

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2003

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Phase diagrams of mixed alkylglucoside surfactants, n-nonyl β-D-glucopyranoside and n-decyl β-D-glucopyranoside (C9G1 and C10GI, respectively) have been examined for the purpose to determining the micellar microstructure surrounding a closed-loop liquid-liquid miscibility gap. NMR self-diffusion, cryo-TEM and TRFQ experiments show the presence of long interconnected networks of rod-like micelles throughout the micellar region of the ternary C9G1/C10G1/H2O phase diagram. Scale models indicate that the networks in the C9G1 rich section of the micellar region have scissions, whereas those in the C10G1 rich region of the phase diagram do not. This likely accounts for the differences in the phase diagrams of C9G1/water and C10G1/H2O. The pKa of a fatty acid probe at the interface of a variety of alkylglucoside surfactants, C9G1, C10G2, C12G2 and C12G3 was measured. Chain length, headgroup size and concentration had no significant effect on the average measured pKa of 6.3, indicating that the surfactants are truly nonionic. The value of the pKa of the probe in these surfactants also indicates that they are better hydrated than the nonionic ethylene oxide surfactants. Due to the value of the pKa, this class of nonionics provides a better pKa(0) reference for calculation of electric potential at interfaces. Finally, investigations into the influence of nonionic micelles on dephosphorylation reactions were conducted in nonionic ethylene oxide surfactants of differing headgroup size, and the effect of ethylene oxide versus alkylglucoside surfactants on nucleophilic substitution reactions was also investigated. Reaction mechanisms in micellar media can differ quite a bit from those in organic solvents of similar dielectric constant, due to the differences in hydration of the media. For nucleophilic substitution reactions, deprotonated surfactants behave as nucleophiles, forming an intermediate ether with the substrate. Reaction mechanisms were determined by 31P, 19F and 1H NMR.