The nematic-isotropic two phase region in mixtures of quasi-spherical solutes in alkylcyanobiphenyls: An E.S.R. study using tempone as probe |
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Authors: | G. A. Oweimreen J. S. Hwang |
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Affiliation: | a Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia |
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Abstract: | The transitional behaviour of binary mixtures, each containing a non-mesomorphic quasi-spherical solute at a low mole fraction in a nematogenic solvent, has been investigated by E.S.R. spectroscopy using 4-oxo-2,2,6,6-tetramethyl-4-piperidinyl-1-oxy (tempone) as a spin probe. This approach makes use of the smaller coupling constant obtained for the spin probe in the orientationally ordered nematic phase relative to that obtained in the isotropic phase. The solutes included Et4C (tetraethylmethane) and R4Sn (R = Cb2bH5, n-C3H7 and nCb4H9). The solvents were 4-n-pentyl-4'-cyanobiphenyl (5CB) 4-n-hexyl-4'-cyanobiphenyl (6CB) and 4-n-heptyl-4'-cyanobiphenyl (7CB). This fast approach compares favourably with other studies. In addition it provides the tempone spectral parameter, f, which is a relative measure of the fraction of the nematic phase at different temperatures within the two phase region. |
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