Structural features of the single and mixed micellar systems of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) were characterized using the fluorescence probe 6-propionyl-2-(dimethylamino)naphthalene (Prodan). In particular, our investigations capitalized on the spectral sensitivity of Prodan to its environment as well as the extensive solubility of Prodan in solvents of varying polarity and/or hydrophobicity to effectively use a three-mode factor analysis technique to resolve the coincident emission from Prodan in multiple microenvironments of single and mixed micelle systems. Our investigations reveal parameters of Prodan fluorescence that reflect the relative polarities of the surfaces of SDS and DTAB micellar cores, the permeability of the SDS micelle interface, and the heterogeneity of SDS−DTAB mixed micellar systems. In particular, we observe a strong affinity of Prodan for both SDS and DTAB micelles at the water−surfactant interface with the emission λmax of Prodan consistent with greater water accessibility in the SDS interfacial region. Reduction in SDS head-group repulsion upon the addition of both an alkali metal series of counterions (Li+ → Na+ → K+) and a tetrasubstituted ammonium series of counterions (NH4 + → N(CH3)4 + → N(CH3CH2)4 + → N(CH3CH2CH2CH2)4 +) appears to induce a more nonpolar environment for Prodan. Each one-phase and two-phase region of the dilute aqueous binary SDS−DTAB pseudoternary diagram is identified by distinct Prodan λmax values. Evidence is presented for the presence of SDS−DTAB mixed micelle systems.

The rate of base-mediated ester hydrolysis in monolayers of 11-mercaptoundecyl isonicotinate on gold is monitored by infrared spectroscopy and cyclic voltammetry. The hydrolysis product, a surface-confined alcohol, can be converted to a trifluoroacetate, increasing the sensitivity of infrared monitoring. Pentaammineruthenium(II) can be attached to the pendant isonicotinate either prior to or after monolayer assembly, leading to monolayers with a highly-charged monolayer/solution interface and a built-in electrochemical probe. The rate of ester hydrolysis within the monolayer is controlled by steric factors associated with monolayer packing and by the amount of charge at the monolayer/solution interface. The stability of the pendant Ru(III) complex is very sensitive to pH and interfacial charge. These results are correlated with Gouy-Chapman double-layer theory.