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'High Pressure' in keywords Facet   Publication Year 1995  [X]
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1995[X]
1Author    A. Heinrich-Schramm, W. E. Price, H.-D LüdemannRequires cookie*
 Title     
 Abstract    h e In flu e n c e o f D ip o le -D ip o le I n te r a c tio n a n d H y d r o g e n B o n d in g U p o n T r a n s la tio n a l D iffu s iv ity in S im p le F lu id s Self-diffusion coefficients of dimethylether have been measured as a function of temperature (185-458 K) and pressure (up to 200 MPa) by pulse-gradient field spin-echo NMR. Calculated activation volumes (AV*) fall from 15 (10-6 m3/mole) at the highest temperature to 7 (10~6 m3/mole) at the lowest. This trend is in keeping with values for other non-associating liquids. Comparison with self diffusion data for propane and ethanol reveals that the translational diffusivity in dimethylether is influenced by the substance's modest dipole moment (1.3 Debye). The effect is small but measur­ able and becomes more pronounced at lower temperatures. S e lf-D iffu s io n in C o m p re s s e d D im e th y le th e r : 
  Reference    Z. Naturforsch. 50a, 145—148 (1995); received October 5 1994 
  Published    1995 
  Keywords    Dimethylether, Diffusion, High Pressure 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0145.pdf 
 Identifier    ZNA-1995-50a-0145 
 Volume    50 
2Author    Heinrich-Schramm, W. E. Price, H.-D LüdemannRequires cookie*
 Title     
 Abstract    Self-diffusion in ethanol/hexane and dimethylether/hexane mixtures of various compositions has been measured at 215-350 K and up to 200 MPa. Qualitative analysis of the results indicates that, as expected, hydrogen bonding retards the self-diffusion of ethanol in the mixture, especially at the low temperatures. Dimethylether shows a slight effect of dipole-dipole interactions on the self-diffu­ sion, as seen by a higher AE* value than for the alkane. However there is no significant difference in the pressure dependence for both mixtures. This is shown by considering the ratio of the two diffusion coefficients, which suggests that, contrary to what is observed for pure alcohols, pressure has little effect upon the hydrogen bonding of ethanol in the mixture. In additon, there is surprisingly little concentration dependence on the ratios for either mixture. 
  Reference    Z. Naturforsch. 50a, 149—154 (1995); received October 5 1994 
  Published    1995 
  Keywords    Binary mixtures, Self diffusion, High pressure 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0149.pdf 
 Identifier    ZNA-1995-50a-0149 
 Volume    50 
3Author    Z. NaturforschRequires cookie*
 Title      
 Abstract    The pressure-dependence of the dielectric anisotropy, Ae = e0||— e0±, of two nematogens, n-pentyl-and n-hexyl-cyanobiphenyl (5CB and 6CB) has been measured at constant temperature. For this purpose a high pressure chamber made of non-magnetic materials was constructed, allowing for the orientation of the samples by a magnetic field. The pressure dependencies of Aex were analyzed in the frame of the Maier-Meier equations for the principal permittivity components in the nematic phase. It was found that the relation between Ae and the order parameter S is not properly described by these equations. The Kirkwood correlation factor calculated on the basis of the present results and the Maier-Meier equations is smaller than 0.5, whereas it increases to a more realistic value (~0.7) if the electronic polarization is incorporated in the equations. P r e s s u r e D e p e n d e n c e o f th e D ie le c tric A n is o tr o p y o f 5 C B a n d 6 C B 
  Reference    Z. Naturforsch. 50a, 826—830 (1995); received April 28 1995 
  Published    1995 
  Keywords    Nematic liquid crystals, Cyanobiphenyls, High pressure, Dielectric anisotropy 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0826.pdf 
 Identifier    ZNA-1995-50a-0826 
 Volume    50 
4Author    T. Brückert, D. Büsing, A. Würflinger, S. UrbanRequires cookie*
 Title      
 Abstract    h e r m a l A n a ly s is (D T A) a n d D ie le c tr ic S tu d ie s o f 4 -(tra n s -4 -H e p ty l-C y c lo h e x y l) -b e n z o n itr ile (7 P C H) u n d e r H ig h P r e s s u r e With the aid of DTA the phase diagram of 4-(trans-4-heptyl-cyclohexyl)-benzonitrile, 7PCH, was redetermined. Dielectric studies on the static and complex permittivity have been performed on 7PCH in the pressure range 0.1 -220 MPa, the frequency range 1 kHz-13 MHz and the temperature range 290-380 K. For the slow relaxation process in the nematic phase, characterized by the relaxa­ tion time Tjj , we have calculated the activation volume, A* V u, of about 80 to 60 cm3/mol (decreasing with increasing temperature), and the activation enthalpy, A *Hn, of approximately 70 kJ/mol. The isochoric activation energy, A* Un, amounts to about 36 kJ/mol. The pressure dependence of A * Hu is less pronounced compared with previous findings for 5PCH and 7CB. Estimates of t 0 (extrapo­ lated from the relaxation time in the isotropic phase) allow the calculation of the retardation factor gu = Tn/t0 that is analysed in terms of theories of Martin-Meier-Saupe and Coffey in order to evalu­ ate the nematic potential q. Using data for the order parameter 5 from NMR studies it was possible to determine the strength of the interaction potential in the nematic phase and to check the relation q~S which is valid at p = const., but not at V= const. The results are compared with recent findings for other homologous series. 
  Reference    Z. Naturforsch. 50a, 977—983 (1995); received August 25 1995 
  Published    1995 
  Keywords    Dielectric Relaxation, High Pressure, Liquid Crystals, Activation Parameters, Phase Transitions 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0977.pdf 
 Identifier    ZNA-1995-50a-0977 
 Volume    50 
5Author    Yukihiro Yoshimura, Seiji Sawamura, Yoshihiro TaniguchiRequires cookie*
 Title     
 Abstract    f fe c ts o f P r e s s u r e , T e m p e r a tu r e , a n d C o n c e n tr a tio n o n th e V is c o s ity o f A q u e o u s A m m o n iu m B ro m id e S o lu tio n Dedicated to Prof. Hitoshi Ohtaki on the occasion of his 60th birthday The viscosity of aqueous ammonium bromide solutions is measured at 0.1-1.0 mol kg-1, 278.2-323.2 K, and 0.1-375 MPa, using a high-pressure rolling-ball viscometer. The activation energy (£v) for viscous flow and Jones-Dole's B coefficient are estimated. Ev against pressure yields a concave curve with a minimum and B yields a convex one with a maximum. These phenomena are attributed to pressure, temperature, and concentration effects on the water-structure. 
  Reference    Z. Naturforsch. 50a, 316—322 (1995); received December 14 1994 
  Published    1995 
  Keywords    Viscosity, High pressure, Ammonium bromide, Activation energy, Jones-Dole's B coef­ ficient 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0316.pdf 
 Identifier    ZNA-1995-50a-0316 
 Volume    50