Anisotropic dynamics of guest molecules in aerosol OT lamellar structures

Abstract

The present work is focused on developing a description of an anisotropic microheterogeneous medium, exploiting the dynamics of a guest molecule. The medium in question is the lamellar structures formed in the aqueous layer of ternary mixtures containing aerosol OT (AOT), water and n-heptane. The guest used in this study is the fluorescent probe, coumarin 153 (C153). The dynamics of this molecule, within the lamellar structure, have been studied using a combination of steady state and time resolved fluorescence, as well as fluorescence correlation spectroscopy (FCS). The fluorophore is strongly solvatochromatic and so, the wavelength of excitation can be tuned so as to selectively excite fluorescent molecules residing in different regions of the microheterogeneous media, even if the spatial separation between these regions is below the diffraction limit. The excitation wavelength in the present experiments is chosen so as to exclusively excite those C153 molecules that reside in the hydrophobic region of the lamellar structures. This triggers two different modes of diffusion, one along and the other perpendicular to the bilayers of the AOT. Thus, the dynamics of the fluorescent probe provide an elegant manifestation of the anisotropy of the host medium.

Insight into the Dynamics of Different Fluorophores in the Interior of Aerosol OT Lamellar Structures in the Presence of Sugars: From Picosecond-to-Femtosecond Study

“…As the sample does not form lamellar structure, it cannot polarize light. , AOT solutions having concentrations from ∼12 to ∼78 wt % exhibit lamellar structure, and the X-ray diffraction peaks for these samples originate from the (001) diffracting planes of the lamellar structures . We have prepared a ternary mixture of n -heptane, AOT, and water having W 0 ([H 2 O]/[AOT]) = 150, where ∼16 wt % AOT is present and it forms lamellar structure . In the lower layer of the ternary mixture (AOT, water, and n -heptane), the AOT bilayer forms and its small-angle X-ray scattering (SAXS) data in the absence and presence of 0.15 M sucrose and sucralose are depicted in Figure b.…”

“…Solvation dynamics is a very efficient technique to gain the inner detail of the hydration properties inside various confined media. ,,− ,, Datta and co-workers have studied the solvation dynamics of two fluorophores, C153 and C500, inside the lamellar structures of W 0 = 150 and 300. , Moreover, they have compared the solvation dynamics of another solvatochromic probe Coumarin 102 (C102) inside lamellar structures and in Nafion nanochannels . In this work, we have studied the alteration of the hydration properties of various solvatochromic Coumarin dyes (Coumarin 153, Coumarin 480, and Coumarin 343) in the presence of two sugar molecules (sucrose and sucralose) having distinct features.…”

“…After 2 days, the aqueous and oil phases were completely separated. The upper n -heptane rich layer was discarded and water rich lower layer contained the lamellar structure and it was used for all the experimental purposes. − In the prepared lamellar structure, the molar ratio ([H 2 O]/[AOT]) was 150 and the final concentration of each of the sugars (sucrose and sucralose) inside the lamellae were maintained as 0.15 M and the final concentration of the fluorophores (Coumarin dyes) were ∼3 × 10 –5 M.…”

“…8 We have prepared a ternary mixture of n-heptane, AOT, and water having W 0 ([H 2 O]/[AOT]) = 150, where ∼16 wt % AOT is present and it forms lamellar structure. 52 In the lower layer of the ternary mixture (AOT, water, and nheptane), the AOT bilayer forms and its small-angle X-ray scattering (SAXS) data in the absence and presence of 0.15 M sucrose and sucralose are depicted in Figure 1b. In the SAXS measurement, we obtain a plot of scattering intensity, I(q) vs scattering wave vector (q), and q is also related with the total scattering angle (θ) as follows…”

“…However, they have widely different solubility and hydrophobicity, and their ground- and excited-state electronic properties were characterized by Castner and co-workers using time-dependent density functional theory (TDDFT) methods . Datta and co-workers have investigated the effect of nanoconfined water layers of AOT lamellar structures on the solvation dynamics of various guest molecules like Coumarin 153 (C153), Coumarin 102 (C102), and Coumarin 500 (C500). − Moreover, they have shown that the excited-state intramolecular double proton transfer (ESIDPT) dynamics of [2,2′-bipyridyl]-3,3′-diol, BP­(OH) 2 , get significantly hindered inside the lamellar AOT compared to other microheterogeneous media …”