Diffusion coefficients in anisotropic fluids by ESR imaging of concentration profiles
Date
1986-03-15Author
Hornak, Joseph
Moscicki, J.
Schneider, Donald
Freed, J.
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We report on the use of ESR imaging for determining the translational diffusion constants of typical ESR spin probes in ordered and isotropic solvents. A discussion is given for a Fourier deconvolution method for determining the correct concentration profile if there is more than one hyperfine line in the spectrum of the radical as well as a spatial dependence of the spectrometer sensitivity. A simple but approximate subtraction deconvolution method is also presented. The diffusion constants for 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPONE) in the nematic and isotropic phases of the liquid crystal p-pentylbenzylidine-p-butylanaline (5,4) were determined. In the isotropic phase the diffusion coefficient is isotropic (D=2.5×10–6 cm2 s–1, at 50 °C), while in the nematic phase it was found to be mildly anisotropic. The diffusion coefficients for motion perpendicular and parallel to the director axis in the nematic phase are respectively, D =9.0×10–7 cm2 s–1, D =6.4×10–7 cm2 s–1 at 27 °C. This is interpreted in terms of some smectic-like character in the nematic phase of 5,4. Possible improvements in the technique are also discussed. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.