Properties of AOT Aqueous and Nonaqueous Microemulsions Sensed by Optical Molecular Probes

Abstract

Nonaqueous microemulsions of AOT in n-hexane and n-heptane by using six polar solvents as water substitutes such as glycerol (GY), ethylene glycol (EG), propylene glycol (PG), formamide (FA), dimethylformamide (DMF), and dimethylacetamide (DMA) were studied and compared with the corresponding aqueous reverse micelles. The microenvironment generated by these systems was sensed by following the solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB). By varying Ws (Ws ) [polar solvent]/[AOT]), the existence of an interaction between the hydrogen bond donor solvents EG, PG, and FA and QB was detected by the changes in the absorption spectra. These changes were interpreted as caused by the partition of the probe between the micelle interface and the polar solvent core by hydrogen bond interactions. The hydrogen bond association constants were calculated, being the largest for FA. In the case of GY, as well as for water, QB seems to be anchored at the interface and no partition was detected. For solvents with no hydrogen bond donor ability such as DMF and DMA the polarity sensed by QB increases with Ws being always larger than the polarity of the neat solvent. The value of the critical micellar concentration (cmc) was also investigated by using acridine orange base as absorption and fluorescence probe. The values of the cmc found for these systems are around (7 ( 2) × 10 -3 M which are higher than those for AOT in comparable aqueous systems.

Binding of o-nitroaniline to nonaqueous AOT reverse micelles

“…Moreover, it was shown that the micropolarity of the AOT reverse micelle interface was greater than that corresponding to the bulk DMF and DMA. 33 These facts explain satisfactorily the high values for the K b values obtained and confirm that the sulfonate group was "bare" in these reverse micelles and consequently more able to hydrogen bond to the solute.…”

Comparison Between Aqueous and Nonaqueous AOT-Heptane Reverse Micelles Using Acridine Orange as Molecular Probe

“…The microemulsions can be characterized by using molecular probes such as: 1-methyl-8-oxyquinolinium betaine (QB) or the free base of the dye acridine orange AO [2]. The aim of the present contribution is to investigate the properties of the base AO in aqueous and nonaqueous AOT/n-heptane microemulsions.…”

Study of Influence of Salt Additives on Mixed Reverse Micelles via Reverse Microemulsion Chromatography and UV–visible Spectroscopy

“…o-Nitroaniline (o-NA) is a very convenient molecular probe because the binding constants to the micelle can be determined by UVvisible spectroscopy. 7,8 The goal of the proposed work was to study the influence of different kosmotropic and chaotropic additives introduced in the water pockets of reverse micelles on both the chromatographic retention factor of model compounds and binding of a molecular probe to reverse micelles, by using reverse microemulsion chromatography and ultravioletvisible spectroscopy.High-performance liquid chromatographic (HPLC) analyses were carried out with a microcolumn liquid chromatograph "Milichrom-4" (Nauchpribor, Oryol, Russia) equipped with an isocratic pump and a variable-wavelength UV detector. The detection of compounds was carried out at ambient temperature.…”

“…o-Nitroaniline (o-NA) is a very convenient molecular probe because the binding constants to the micelle can be determined by UVvisible spectroscopy. 7,8 The goal of the proposed work was to study the influence of different kosmotropic and chaotropic additives introduced in the water pockets of reverse micelles on both the chromatographic retention factor of model compounds and binding of a molecular probe to reverse micelles, by using reverse microemulsion chromatography and ultravioletvisible spectroscopy.…”