Sugosh Prabhu - Rotational Diffusion of Organic Solutes in 1-Methyl-3-octylimidazolium Tetrafluoroborate–Diethylene Glycol Mixtures: Influence of Organic Solvent on the Organized Structure of the Ionic Liquid

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        Radiation and Photochemistry Division, Bhabha Atomic Research     Centre Trombay, Mumbai 400 085, India 
    J. Phys. Chem. B, 2014, 118 (20), pp 5562–5569
    Publication Date (Web): May 6, 2014
    Copyright © 2014 American Chemical Society


        Rotational diffusion of two structurally similar organic solutes,   9-phenylanthracene (9-PA) and rhodamine 110 (R110), has been   investigated in 1-methyl-3-octylimidazolium   tetrafluoroborate–diethylene glycol ([MOIM][BF4]–DEG)   mixtures to understand the influence of organic solvent on the   organized structure of the ionic liquid. The reorientation times   (τr)   of nonpolar and charged solutes have been measured as a function   of viscosity (η) by changing the temperature (T)   as well as the composition of the ionic liquid–organic solvent   mixture. These results when analyzed using the   Stokes–Einstein–Debye (SED) hydrodynamic theory follow the   relationship τr    = A(η/T)n,   where A    is the ratio of hydrodynamic volume of the solute to Boltzmann   constant. However, in neat [MOIM][BF4]   and up to 0.4 mole fraction of DEG (xDEG),   significant deviations from the SED hydrodynamic theory have been   noticed with n    being much less than unity. As xDEG    is increased further, the parameters A    and n    increase considerably for both solutes, and their rotational   diffusion follows the predictions of the SED hydrodynamic theory.   It has also been observed that the trends in the variation of   τr    with η/T    for 9-PA and R110 are not similar. These observations have been   rationalized by taking into consideration the organized structure   of the ionic liquid, which gradually becomes homogeneous at the   microscopic level with the addition of the organic   solvent.

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