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2409to the donor concentrations and the blue shift of iodine visible maximum on mixing with the donor were the experimental results for the ETU-iodine system.Proceeding as before, values of KAB, AH", and AS" were computed. The average K A B is found to be 558 a t 29" (less than that of DPT-iodine complex). Table I1 compares the values of AH" and AS" for complexation of some thioamides and iodine. Enthalpy as well as entropy of formation of ETU-iodine complex are much less than those of DPT-iodine complex. This goes along with the low enthalpy and entropy of formation of tetramethylthiourea-iodine complex as compared with those of di-tert-butylthiourea-iodine ~omplex.'~ In fact we expect ETU to be a weaker donor than tetramethylthiourea. The Breigleb equation was used to get an estimate of the ionization potential of ETU. A value of 7.71 eV was obtained for its first ionization potential. Publication costs assisted by the Air Force Ofice of Scientific ResearchThe dynamic shear properties of p-rnethoxybenzylidene-p-n-butylaniline (MBBA) in its nematic and isotropic states are studied in the temperature range 25 to 65" using a shear reflectance technique. Shear wave frequencies from 2.75 to 10 MHz are used, and three orientations of the preferred direction of the molecular axis with respect to the direction of polarization of the shear wave are considered. The anisotropy ratio for the dynamic viscosity is about 2; the ratio for the shear modulus is highly frequency dependent, being as large as 3.5. Approximations are made which allow the Leslie-Ericksen coefficients to be calculated.

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