Intramolecular Charge Transfer Reaction, Polarity, and Dielectric Relaxation in AOT/Water/Heptane Reverse Micelles: Pool Size Dependence

Intramol. charge transfer (ICT) reaction in a newly synthesized mol., of 4-(41-morpholinyl) benzonitrile (M6C), in AOT/water/heptane reverse micelles at different pool sizes has been studied by using steady-state and time-resolved fluorescence emission spectroscopy. The pool size dependences of the reaction equil. const. and reaction rate have been explained in terms of the av. polarity of the confined solvent pools estd. from the fluorescence emission Stokes shift of a nonreactive probe, coumarin 153, dissolved in these microemulsions. The complex permittivity measurements in the frequency range 0.01 ≤ ν/GHz ≤ 2 for these microemulsions at different pool sizes (0 ≤ w ≤ 40) and AOT concns. (0.1 ≤ c/M ≤ 0.5) at 298.15 K have also been performed. At sufficient water content, a large dispersion with a relaxation time of ∼600 ps has been obsd. at ∼300 MHz and attributed to the av. reorientation of water mols. residing in the close vicinity of the polar interface of the AOT headgroup and n-heptane. The reorientation of these interfacial water mols. is probably responsible for the nanosecond component obsd. in numerous polar solvation dynamics expts. in these reverse micelles. Subsequently, the estd. polarity and the measured reorientational time scale have been used to explain the dramatic slowing down of the ICT reaction rate and its dependence on pool size in these confined environments

Solvent Blends Can Control Cationic Reversed Micellar Interdroplet Interactions. The Effect of n-

We have investigated, for the first time, the effect of the composition of the nonpolar organic media on the benzyl-n-hexadecyl-dimethylammonium chloride (BHDC) reversed micelles (RMs) properties at fixed temperature. To achieve this goal we have used the solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB) as absorption probe and dynamic light scattering (DLS), to monitor droplet sizes, interfacial micropolarity, and sequestrated water structure of water/BHDC/n-heptane:benzene RMs. DLS results confirm the formation of the water/BHDC/n-heptane:benzene RMs at every n-heptane mole fraction (X Hp) investigated, that is, XHp = 0.00, 0.13, 0.21, 0.30, and 0.38. Also, DLS was used to measure the RMs diffusion coefficient and to calculate the apparent droplet hydrodynamic diameter (dApp) at different compositions of the nonpolar organic medium. The data suggest that as the n-heptane content increases, the interdroplet attractive interactions also increase with the consequent increment in the droplet size. Moreover, the interdroplet attractive interactions can be "switched on (increased)" or "switched off (decreased)" by formulation of appropriate n-heptane:benzene mixtures. Additionally, QB spectroscopy was used to obtain the "operational" critical micellar concentration (cmc) and to investigate both the RMs interfacial micropolarity and the sequestrated water structure in every RMs studied. The results show that BHDC RMs are formed at lower surfactant concentration when n-heptane or water content increases. When the interdroplet interaction "switches on", the RMs droplet sizes growth expelling benzene molecules from the RMs interface, favoring the water-BHDC interaction at the interface with the consequent increases in the interfacial micropolarity. Therefore, changing the solvent blend is possible to affect dramatically the interfacial micropolarity, the droplet sizes and the structure of the entrapped water.Fil: Agazzi, Federico Martin. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Falcone, Ruben Dario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Silber, Juana J.. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Correa, Nestor Mariano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin