| | 1 | Author
| M. Sandmann, A. Würflinger | Requires 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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| default:Reihe_A/53/ZNA-1998-53a-0233.pdf | | | | Identifier
| ZNA-1998-53a-0233 | | | | Volume
| 53 | |
| 2 | Author
| M. Sandmann, A. Würflinger | Requires 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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| default:Reihe_A/53/ZNA-1998-53a-0787.pdf | | | | Identifier
| ZNA-1998-53a-0787 | | | | Volume
| 53 | |
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