The long-time self-diffusion coefficients of Triton X-100 micelles have been determined as a function of surfactant and electrolyte concentrations using rotating disk electrode voltammetry in conjunction with ferrocene acting as an electroactive probe. Micellar diffusion conforms to the linear interaction theory and yields micellar hydrodynamic radii values and interaction parameters as a function of electrolyte concentration. The interaction parameters varied from 3.4 to 3.6 over the electrolyte concentration range 0.01−0.8 mol dm-3 KCl, which is consistent with excluded volume interactions and indicated the absence of significant micellar shape changes with the addition of electrolyte. Micellar hydrodynamic radii varied linearly with respect to [KCl] from 4.22 to 6.21 nm, indicating the progressive evolutionary growth of the oblate micelles due to increasing aggregation number and “hydration”. The semimajor to semiminor axial ratio (a/b) increased from 2.0 to 3.5, indicating evolution to a more asymmetric structure. Micellar molecular weights increased from 77 700 to 326 000 over the electrolyte concentration range studied, which is predominantly due to water entrapment at the periphery of the self-assembled structures. Intrinsic viscosities were found to decrease from 6.09 to 4.61 cm3 g-1, indicating a decrease in specific micellar volume, which may be attributed to ethylene oxide chain collapse due to dehydration. The decrease in micellar specific volume was found to correlate precisely with the electrolyte induced decrease of the cloud point.

Densely packed interfacial nanoparticle films form spontaneously when aqueous Ag colloid is shaken with CH2Cl2 in the presence of a "promoter" such as 10(-4) mol dm(-3) tetrabutylammonium nitrate (TBA(+)NO3(-)), which induces rapid self-assembly of the nanoparticles at the liquid/liquid interface without adsorbing onto their surfaces. The particles within these reflective, metal-like liquid films (MeLLFs) are optically coupled and give strong SERS enhancement, similar to that obtained for the same colloid aggregated with optimized concentration of metal salt. However, unlike aggregated colloids their structure means they do not sediment out of solution so they give SERS spectra that are stable for >20 h) and have good uniformity (relative standard deviation in absolute intensity over 1 mm(2) array of 25 points was 1.1%). Since the films lie at the aqueous/organic interface they are open to adsorption of analytes from either of the phases and can be probed in situ to detect both water- and nonwater-soluble analytes. The detection limit for mercaptobenzoic acid (MBA) added to the organic layer was found to be <2 ppb. These materials therefore combine many of the best features of both patterned surfaces and metal colloids for quantitative SERS analysis.

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Two electrochemical techniques have been used to measure the pK(a) of N-bases in several ionic liquids (ILs). The first method corresponds to a potentiometric titration of a strong acid with the N-base using a platinized Pt indicator electrode immersed in the IL solution and maintained under dihydrogen atmosphere via gas bubbling. The second approach involves performing cyclic voltammetry at a platinized Pt electrode in a solution containing both strong acid and the conjugate weak acid of the N-base. Values of pK(a) obtained by one or the other approach are in good agreement with each other. The experimental data clearly demonstrated that acid/base chemistry in ILs is similar to that observed in molecular nonaqueous solvents; i.e., the relative strengths of the bases were in the right order and spaced (ΔpK(a)). It was also observed that the strength of N-bases is highly dependent on the anion of the ionic liquid; this observation indicates that pH-dependent reactions could be controlled by the appropriate choice of anion for bulk ILs or as an added co-ion to bulk IL.