Effect of CO₂ on the Properties of AOT/Water/Isooctane Reverse Micelles by Fluorescence Study

Abstract

The effect of compressed CO 2 on the properties of sodium bis(2-ethylhexyl) sulfosuccinate/water/isooctane reverse micelles was investigated by steady-state and time-resolved fluorescence spectroscopic techniques. With the solvatochromic fluorescent probe 6-propionyl-2-(dimethylamino)-naphthalene, the steady-state fluorescence spectroscopy indicates a changed environment in multiple microregions of the reverse micelles with increasing CO 2 pressure. Quantitative estimates for the micropolarities of micellar cores at different pressures were carried out in terms of the empirical polarity parameter E T (30). The results show that E T ( 30) is gradually increased with the pressure. The emission of 8-anilino-1-naphthalenesulfonic acid indicates a reduced viscosity inside the micellar cores. Its reduced lifetime characterizes the dynamic property of solvent reorientation within micellar cores increases with the increasing CO 2 pressure.

Effect of Compressed CO2 on the Critical Micelle Concentration and Aggregation Number of AOT Reverse Micelles in Isooctane

“…The high-pressure fluorescence cell was similar to that used previously. [21] ANS was used as the external fluorescence probe and CPC was employed as the quencher. [44] The excitation wavelength was 346 nm, and the fluorescence emission was measured at 455 nm.…”

“…[11][12][13] In addition, extensive research has been done to study the properties of reverse-micellar systems, such as the micropolarity and microviscosity of the water core, micellar size, and thermodynamics. Many techniques, such as UV/Vis spectroscopy, [14][15][16] FTIR spectroscopy, [17][18][19] fluorescence spectroscopy, [20,21] small-angle neutron scattering analysis, [22,23] small-angle X-ray scattering analysis, [24,25] and microcalorimetry [26][27][28] have been used to characterize reverse-micellar solutions. In recent years, microemulsions with supercritical CO 2 as the continuous phase have been studied extensively.…”

Reversible Switching of a Micelle‐to‐Vesicle Transition by Compressed CO2

“…The experimental procedures were also similar to those reported previously. [57] In the experiments, pyrene was used as the fluorescence probe, and CPC (see Scheme S1 in the Supporting Information) to quench the probe. The desired amounts of pyrene in ethanol and CPC in water were added to the surfactant solution directly, and the solution was stirred vigorously for 48 h. The concentration of pyrene was kept low (1 mm) to prevent excimer formation.…”

“…[57] The cell was composed mainly of a stainless-steel body with four channels, four-quartz windows (diameter: 1.6 cm, thickness: 0.7 cm). The inner volume of the sample cell was 8.44 mL and was thermostated to AE 0.2 8C of the desired temperature with a heater and temperature controller.…”

“…[56,57] The apparatus consisted mainly of a gas cylinder, a high-pressure pump, fluorescence spectrophotometer (F-2500, Hitachi), and a high-pressure fluorescence sample cell. The emission spectra were recorded on the spectrophotometer equipped with a computer.…”