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The aqueous environment in AOT and Triton X-100 (w/o) microemulsions probed by fluorescence

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Abstract

The confined aqueous medium of Triton X-100/cyclohexane-hexanol/water microemulsions was studied and compared with that of AOT/isooctane/water. The microenvironment generated was assessed by following the photophysical behaviour of the cationic dye, acridine orange (AO). This dye presents an acid-base equilibrium in free bulk water (pKa ≈ 10.2) which is clearly affected in Triton X-100 microemulsions where the neutral species is stabilised at low ω0. The addition of water contributes to the appearance of the protonated species. This, however, presents spectral features that show a less polar and/or protic character of the encapsulated water even at high contents. The “anomalous” microviscosity dependence on the amount of solubilised water (ω0 = [H2O]/[Surf]) in Triton X-100 microemulsions obtained from steady-state anisotropy data was used to discuss the existence of bulk free water within these confined media, where at ω0= 8, properties seem to change. In AOT, a complex AO-AOT is detected in equilibrium with the protonated AO, at pH = 7. The two-state excited-state formalism was applied to describe the transient data which in the case of AOT introduces a rate constant that accounts for the water quenching (kq = 0.51 ± 0.03 × 108 M1 cm1).

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  1. Centro de Química Estrutural, Complexo 1, Instituto Superior Técnico, 1049-001, Lisboa Codex, Portugal

    Suzana M. Andrade & Sílvia M. B. Costa

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  1. Suzana M. Andrade
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  2. Sílvia M. B. Costa
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Andrade, S.M., Costa, S.M.B. The aqueous environment in AOT and Triton X-100 (w/o) microemulsions probed by fluorescence. Photochem Photobiol Sci 1, 500–506 (2002). https://doi.org/10.1039/b201477g

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