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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 
3Author    M. Sandmann, F. Hamann, A. WürflingerRequires cookie*
 Title    PVT and DTA Measurements on trans-4-w-Hexyl- (4'-CyanophenyI)-Cyclohexane (6PCH) up to 300 MPa  
 Abstract    The phase diagram of trans-4-n-hexyl-(4'-cyanophenyl)-cyclohexane, (6PCH) has been estab-lished by high-pressure differential thermal analysis. Specific volumes are presented for temper-atures between 300 and 370 K up to 300 MPa. The p,V m ,T data have been determined for the nematic, isotropic, and (partly, in the neighbourhood to the melting curve) solid phases. Volume and enthalpy changes along the phase transitions have also been calculated. As previously, the p,Vm,T data were used to calculate the volume entropy for the nematic-isotropic transition. The molar volumes along the clearing line T NI (p) enabled us to calculate the molecular field parameter 7 = ain T NI /3ln V NI , being 4.1. 
  Reference    Z. Naturforsch. 54a, 281—286 (1999); received March 13 1999 
  Published    1999 
  Keywords    6PCH, High Pressure, pVT, Phase Transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0281.pdf 
 Identifier    ZNA-1999-54a-0281 
 Volume    54 
4Author    M. Sandmann, F. Hamann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4-/i-Pentyl-4'-Cyano-Biphenyl (5CB) and trans-4-(4'-Octyl-Cyclohexyl)-Benzonitrile (8PCH) up to 300 MPa  
 Abstract    Specific volumes are presented for 4-n-pentyl-4'-cyanobiphenyl (5CB) and trans-4-(4'-octyl-cyclo-hexyl)-benzonitrile (8PCH) for temperatures between 300 and 370 K up to 300 MPa. The p,V m ,T data were determined for the liquid crystalline and isotropic phases, and partly also for the solid phase adjacent to the melting curve. Stable and metastable crystal phases can be distinguished. The density and melting temperature of the metastable form are lower than for the stable one. Volume and enthalpy changes accompanying the phase transitions are reported as well. The p,V m ,T data allow to calculate the entropy change for a hypothetical transition at constant volume. The molar volumes along the nematic-isotropic phase transition T NI (p) allow to determine the molecular field parameter y = S In T NI /0 In F N ,. 
  Reference    Z. Naturforsch. 52a, 739—747 (1997); received August 13 1997 
  Published    1997 
  Keywords    5CB, 8PCH, High pressure, pVT, Phase transitions, Thermodynamics, DTA 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0739.pdf 
 Identifier    ZNA-1997-52a-0739 
 Volume    52 
5Author    Albert Würflinger, Denise Mondieig3, Fazil Rajabalee3, MiquelAngel Cuevas-DiartebRequires cookie*
 Title    pVT Measurements and Related Studies on the Binary System /iC16H34 -tiC17H36 and on wC18H38 at High Pressures  
 Abstract    The phase diagram of the binary system nC16H34 -rcC17H36 has been established at ambient pressure using DSC and crystallographic measurements. At low temperatures below the rotator phase RI there exist two crystal forms Op (about jc(C17) = 0.25) and Mdci (about x(C17) = 0.67) which are different from the crystal structures of the pure compounds (Tp for C 16 and Oi for C 17). Furthermore two compositions: (a) C 16/C 17 = 3:1 and (b) = 1:2, which correspond to the coexistence range of Op and Mdci, were chosen for high pressure DTA and pVT measurements, yielding the following findings: The specific volume of the rotator phase of C 17 is distinctly lower than those of the binary systems at the same state point. Assuming the existence of a metastable rotator phase for C 16, an excess volume of A V E/V « 0.01 can be estimated. Due to the very enlarged coexistence range of RI, the mixtures reach their lower transition point at considerably lower temperatures (in isobaric measurements) or higher pressures (in isothermal measurements), where the specific volume is lower than that of C 17 at its transition point. Furthermore, the volume and enthalpy changes of the O ord -RI transition is distinctly smaller for the binary systems than for pure C 17. Thus the specific volumes of the phases Op and Mdci are appreciably larger than t>(spec.) of C 17. Op and Mdci have practically the same specific volume in accordance with the crystallographic results. Enthalpy values are obtained with the aid of the Clausius-Clapeyron equation which agree well with enthalpies derived from the DSC measurements. Furthermore, pVT data have been established for the liquid and solid phases of nC18H38 in the neighbourhood of the melting curve, allowing to determine volume and enthalpy changes of melting as a function of pressure. 
  Reference    Z. Naturforsch. 56a, 626—634 (2001); received July 18 2001 
  Published    2001 
  Keywords    Hexadecane, Heptadecane, Octadecane, pVT, Excess Volume, Phase Transition, High Pressure, X-ray 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0626.pdf 
 Identifier    ZNA-2001-56a-0626 
 Volume    56