Richard R. M. Jones

Effect of 1-butanol on the surface structure of ionic micelles and location of its solubilization site: electron spin echo modulation study with x-doxylstearic acid spin probes

Abstract Electron spin echo modulation studies with a series of x-doxylstearic acids (x = 5, 7, 10, 12, and 16) have been carried out for sodium- and tetramethylammonium dodecylsulfate and dodecyltrimethylammonium chloride frozen micellar solutions containing protiated and perdeuterated 1-butanol. Modulation effects due to nitroxide interactions with deuterium in water and butanol have been measured versus doxyl group position. The effect of 1-butanol on the micellar surface and internal micellar structure has been evaluated and the average location of 1-butanol in these micelles has been deduced to be in the outer annulus of the micelle core.

Effect of added sodium chloride on the molecular environment and photoionization of N,N,N′,N′‐tetramethylbenzidine in micellar solutions as studied by electron spin echo and electron spin resonance spectroscopy

The electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the cation radical of N,N,N′,N′‐tetramethylbenzidine (TMB) in frozen sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) micelles were studied as a function of sodium chloride concentration. TMB+⋅ was produced by photoionization at 350 nm of the parent compound in the micelles at 77 K. From the ESEM analysis it is found that the cation–water interactions increase with salt addition in both anionic and cationic micelles to a maximum near 0.2 M NaCl and then decrease somewhat. The increase is interpreted in terms of an increase in the water density at the micellar surface due to an increased surface concentration of hydrated counterions. The decrease may be due to TMB moving further from the polar micellar surface with added salt. From ESR spectra the photoionization yields of TMB at 77 K were determined. For DTAC micelles the yields are found to decrease with salt addition as expected from electrosta...

Small-angle neutron scattering from an oil-in-water microemulsion as a function of temperature

Abstract A multicomponent oil-in-water microemulsion containing CTAB (C 16 H 33 NMe 3 Br), n -octane, 1-butanol, NaBr, and D 2 O has been studied by small-angle neutron scattering at several temperatures. The size of the microemulsion droplets was found to be independent of temperature. Correlation lengths for the critical concentration fluctuations agree with those determined earlier by light scattering.

Electron Spin Echo Modulation Studies of Doxylstearic Acid Nitroxide Spin Probe Locations in Micelles

Electron spin echo modulation spectrometry has been used to probe the weak electron-nuclear hyperfine interactions of x-doxylstearic acid spin probes in frozen micellar systems prepared in D2O or with specifically deuterated surfactant molecules. Spin probes with x = 5, 7, 10, 12, and 16 were used. The surfactant molecules were synthesized with deuterium labels in the polar headgroup or counterion and at the terminal methyl group of the nonpolar alkyl tail. Anionic micelles were prepared from sodium and tetramethylammonium dodecylsulfate surfactants. Cationic micelles were prepared from dodecyltrimethylammonium bromide and hexadecyltrimethyl- ammonium bromide. It is concluded that the sodium dodecylsulfate micelles have a reasonably compact headgroup structure with a low degree of water penetration and relatively well organized alkyl chains with the terminal alkyl groups concentrated near the center region of the micelle. In contrast, the tetramethylammonium dodecylsulfate micelles show a more open headgroup structure with significant water penetration into the Stern region and a locus of terminal alkyl groups that is broadly distributed throughout the micelle. Nitroxide spin probe molecules can have a folded conformation in both anionic and cationic micelles.

Electron spin-echo studies of doxylstearic acid spin probes in microemulsions

We have probed the molecular interactions in the surfactant–cosurfactant sheath of frozen water-in-oil (w/o), oil-in-water (o/w) and middle-phase microemulsions composed of water, sodium dodecyl sulphate (SDS), butan-l-ol, toluene and NaCl by performing two-pulse electron spin-echo modulation (e.s.e.m.) analyses for a series of x-doxylstearic acid spin probes with x= 5, 7, 10, 12 and 16. The microemulsions were prepared with deuterium labels in D2O, [2H10]butan-l-ol or [2H8]toluene. The data correlate well with the now accepted interface structure consisting of SDS and butanol molecules separating the water-rich and oil-rich domains. The surfactant sheath is free of water molecules but contains alcohol molecules in the head-group region and substantial amounts of toluene in most of the alkyl-tail region. The differences observed between the o/w, w/o and middle phases can be ascribed to changes in the lipophilic character of the systems.