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'Thermodynamics' in keywords Facet   Publication Year 1998  [X]
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1998[X]
1Author    M. Sandmann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4'-w-Hexyl-Biphenyl-4-Carbonitrile (6CB) and 4 -w-Heptyl-Biphenyl-4-Carbonitrile (7CB) up to 300 MPa  
 Abstract    P, V m , 7" data were established for 4'-n-hexyl-biphenyl-4-carbonitrile (6CB) and 4'-n-heptyl-biphen-yl-4-carbonitrile (7CB) between 300 and 370 K up to 300 MPa, and specific volumes were determined for the liquid crystalline, isotropic, and also partly for the crystal phases. Volume and enthalpy chang-es at the phase transitions are also presented. In the case of 6CB, a new crystal phase has been detect-ed, corresponding to a triple point at 338 K and 196 MPa. The p, V m , T data enabled us to separate the entropy change into a volume-dependent part and configurational part. From the molar volumes along the nematic-isotropic phase transition T Nl (p), the molecular field parameter y= 3lnT NI /3ln V NI was deter-mined. 
  Reference    Z. Naturforsch. 53a, 233—238 (1998); received March 11 1998 
  Published    1998 
  Keywords    6CB, 7CB, High Pressure, pVT, Phase transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0233.pdf 
 Identifier    ZNA-1998-53a-0233 
 Volume    53 
2Author    M. Sandmann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4'-/i-Octyl-Biphenyl-4-Carbonitrile (8CB) up to 300 MPa  
 Abstract    P, V m , Tdata have been measured for the smectic, nematic and isotropic phases of 4'-n-octyl-biphen-yl-4-carbonitrile (8CB) in the temperature range 300-370 K and pressures up to 300 MPa. At atmos-pheric pressure all phase transitions appear to be of first order due to a discontinuity in the density. The volume change at the smectic A -nematic transition is only a tenth of the volume change at the clear-ing temperature. At moderate pressures below 80 MPa the S A -N transition could be detected as a dis-continuity in the period of oscillation in measurements with a high-pressure vibrating tube densimeter. At higher pressures the discontinuity seems to die away, possibly indicating a change from first order to second order transition. From the volume changes and the slopes of the transition lines we calculate the enthalpy changes at the phase transition. The p, V m , T data enable us to calculate the volume part of the entropy and the molecular field parameter y=9ln 7 N i/3ln V NI . 
  Reference    Z. Naturforsch. 53a, 787—792 (1998); received July 10 1998 
  Published    1998 
  Keywords    8CB, High Pressure, pVT, Phase Transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0787.pdf 
 Identifier    ZNA-1998-53a-0787 
 Volume    53