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'Rotational diffusion' in keywords
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1995 (1)
1992 (1)
1Author    U. Schlenz, A. Dölle, H. G. HertzRequires cookie*
 Abstract    o le c u la r M o tio n in L iq u id s : T h e P a r ti a ll y R ig id M o le c u le 1,2 ,3 » 4 -T e tr a h y d r o -5 ,6 -D im e th y l-l ,4 -M e th a n o n a p h th a le n e . T e m p e r a tu r e D e p e n d e n c e o f 13C M a g n e tic R e la x a tio n a n d C o r r e la tio n T im e s Dedicated to Professor W . Müller-Warmuth on occasion of his 65 th birthday For the hydrocarbon l,2,3,4-tetrahydro-5,6-dimethyl-l,4-methanonaphthalene (5,6-Me2-THMN) 13C longitudinal relaxation times and NOE factors were measured over a wide temperature range at frequencies of 22.63 and 100.62 MHz. Additionally, 13C transversal relaxation times were mea­ sured at 100.62 MHz. The relaxation data show that the dispersion region is already reached at moderate temperatures. The experimental data were modeled by the combination of the Vogel-Fulcher-Tammann ansatz and a scaling of the dipolar coupling constant with a factor of 0.70. From the fit of the data also activation parameters of the rotational motion of the molecules were obtained. Although the molecules of 5,6-Me2-THMN have a rigid structure (except the two inter­ nally rotating methyl groups), the model of the rotational diffusion of rigid bodies does not satisfactorily describe the relaxation data. 
  Reference    Z. Naturforsch. 50a, 631—642 (1995); received December 16 1994 
  Published    1995 
  Keywords    Liquids, Rotational Diffusion, Rotational Correlation Times, 13C Nuclear Magnetic Resonance, Relaxation 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0631.pdf 
 Identifier    ZNA-1995-50a-0631 
 Volume    50 
2Author    V. I. StepanovRequires cookie*
 Title    Comment on the Osipov-Terentjev Calculation of the Viscosity of Liquid Crystals  
 Abstract    The calculation of the viscosity of liquid crystals based on the rotational diffusion approximation recently reported by Osipov and Terentjev [1 a] is critically examined. It is shown that the main result of their treatment -the evaluation of the activational exponent -arises from the neglect of the second derivative of the distribution function with respect to the azimuthal angle in the Fokker-Planck equation. The correct asymptotic formula for the rotational viscosity coefficient is derived. 
  Reference    Z. Naturforsch. 47a, 625—626 (1992); received August 8 1991 
  Published    1992 
  Keywords    Liquid crystal, Viscosity coefficient, Rotational diffusion, Fokker-Planck equation, Energy barrier 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0625_n.pdf 
 Identifier    ZNA-1992-47a-0625_n 
 Volume    47