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1Author    M. Massalska-Arodź, A. Würflinger, D. BüsingRequires cookie*
 Title    High-pressure DTA Studies of the Phase Behaviors of 4-n -butyl-thiocyanobiphenyl (4TCB) and 4-w-pentyl-4'-n-phenyl-cyanocyclohexane (5HCP)  
 Abstract    DTA measurements of 4-/i-butyl-thiocyanobiphenyl (4TCB) and/?-cyano-/?'-pentylphenyl-cyclohex-ane (5HCP) have been performed in the temperature range 220 K-390 K and pressures up to 400 MPa. For 4TCP a transition from a crystalline to a liquid crystal phase (probably smectic E) could be detect-ed at higher pressures > 90 MPa. The pressure dependence of the transition temperature has been estab-lished. At pressures lower than 88.7 MPa no transition of SmE into a crystal or into a glass has been found. For 5HCP only the melting curve was observed, in contrast to 5PCH, which displays a liquid crystalline nematic phase. 
  Reference    Z. Naturforsch. 54a, 675—678 (1999); received November 5 1999 
  Published    1999 
  Keywords    DTA, High Pressures, Phase Transitions, Liquid Crystals 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0675.pdf 
 Identifier    ZNA-1999-54a-0675 
 Volume    54 
2Author    A. Wiirflinger, M. SandmannRequires cookie*
 Title    Thermodynamic Measurements on w-Hexadecane (C 16 H 34 ) and /z-Heptadecane (C 17 H 36 ) at Elevated Pressures  
 Abstract    Specific volumes of/7-hexadecane (H-Ci 6 H 34) and n-heptadecane (fl-C 17 H 36) are presented for tem-peratures between 298 and 348 K and pressures up to 280 MPa. The melting curve for /7-C j6 H 34 was determined with differential thermal analysis. ThepVTdata are established for the liquid, solid and (in the case of J?-C| 7 H 36) rotator phases. Forn-C 16 H 34 the density immediately below the freezing temper-ature is larger than for n-Ci 7 H 36 immediately below the rotational transition temperature. Changes of volume, enthalpy, and entropy along the phase transitions are reported. The volume change of melting decreases distinctly with increasing pressure, whereas the volume change at the rotational transition is much less pressure-dependent. Enthalpy and entropy changes have been calculated with the aid of the Clausius-Clapeyron equation. 
  Reference    Z. Naturforsch. 55a, 533—538 (2000); received February 16 2000 
  Published    2000 
  Keywords    Hexadecane, Heptadecane, DTA, /?V7, High Pressure, Phase Transitions 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0533.pdf 
 Identifier    ZNA-2000-55a-0533 
 Volume    55 
3Author    Albert Würflinger, M. Massalska-Arodż3, S. Urbanb, W. Weissflogc, S. EmstcRequires cookie*
 Title    Thermodynamic Measurements on the Binary System Bis{[2,2-di(w- hexyloxycarbonyl)ethenyl]phenyl} Biphenyl-4,4'-dicarboxylate and 4-w-Octyloxyphenyl 4-/i-Pentyloxybenzoate at Elevated Pressures  
 Abstract    Thermodynamic measurements have been carried out on the binary system of a swallow-tailed liquid crystal A = bis{[2,2-di(n-hexyloxycarbonyl)ethenyl]phenyl} biphenyl-4,4'-dicarboxylate (4DS6) and B = 4-n-octyloxyphenyl 4-rc-pentyloxybenzoate (5 0 /0 8). A filled smectic A phase is induced in the concentration range 0.11 < xA < 0.75. The maximum of the SmA-N transition temperature (365 K) is observed for xA = 0.33. Dilatometric measurements show that the packing density in the filled phases is increased. High-pressure DTA is employed in order to investigate the coexistence range of the liquid crystalline phases and the slopes of the transition lines. The slopes of the melting curves for the mixtures are significantly smaller than those for the pure components. The slopes for the smectic -nematic -isotropic transitions are considerably larger. The coexistence range for the (smectic + nematic) phases does not seem to be pressure-limited, rather it increases with pressure. 
  Reference    Z. Naturforsch. 56a, 658—662 (2001); received July 18 2001 
  Published    2001 
  Keywords    Phase Transitions, DTA, High Pressure, Swallow-tailed Liquid Crystals 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0658.pdf 
 Identifier    ZNA-2001-56a-0658 
 Volume    56 
4Author    H. G. Kreul, R. Waldinger, A. WürflingerRequires cookie*
 Title    Differential Thermal Analysis and Dielectric Studies on Neopentanol under Pressure  
 Abstract    Differential thermal analysis (DTA) and dielectric measurements have been performed on 2,2-di-methyl-l-propanol (neopentanol) up to 200 MPa. Neopentanol exhibits at least one orientationally disordered (ODIC) phase (solid I) that transforms at lower temperatures to a non-plastic phase (solid II). There is evidence of a further ODIC phase denoted as solid I'. The pressure dependence of the phase transitions and the dielectric behaviour up to frequencies of 13 MHz are described. Activation enthalpies and volumes are derived from the dielectric relaxation time and compared with results for other alcohols. 
  Reference    Z. Naturforsch. 47a, 1127—1134 (1992); received July 27 1992 
  Published    1992 
  Keywords    High pressure, DTA, Phase transitions, Dielectric constant, and relaxation 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-1127.pdf 
 Identifier    ZNA-1992-47a-1127 
 Volume    47 
5Author    J. Reuter, T. Brückert, A. WürflingerRequires cookie*
 Title    Differential Thermal Analysis under Pressure on Cyanocyclohexane, 1,2,3,4-Tetrahydro-5,6-dimethyl-1,4-methanonaphthalene, and 2-Methyl-2-propanol  
 Abstract    Differential thermal analysis has been performed on cyanocyclohexane (CCH), 1,2,3,4-tetrahydro-5,6-dimethyl-1,4-methanonaphthalene (TDMN), and 2-methyl-2-propanol (t-butanol) up to 300 MPa. The latter compound was also investigated dielectrically. CCH displays an ODIC phase that transforms only reluctantly to the low-temperature stable phase II. Annealing under pressure can appreciably accelerate this transformation. For all three compounds the phase diagrams were established. For CCH and TDMN also the pressure dependence of the glass transition has been determined. 
  Reference    Z. Naturforsch. 48a, 705—708 (1993); received March 10 1993 
  Published    1993 
  Keywords    High pressure, DTA, Phase transitions, Glass transition, Dielectric constant 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0705.pdf 
 Identifier    ZNA-1993-48a-0705 
 Volume    48 
6Author    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 
7Author    Stanislaw Urban, Albert Wiirflinger3Requires cookie*
 Title    DTA and Dielectric Studies under Pressure of a Smectogen Substance with a Strong Perpendicular Dipole Moment  
 Abstract    The phase diagram of a substance with two CN groups attached to the benzene ring at lateral posi­ tions (CNCN) has been obtained with differential thermal analysis (DTA). The pressure range of the smectic A phase is limited, resulting in a triple point (Cr, SA, L) at 135 MPa and 371 K. However, the SA-phase exists also above the triple point as a metastable phase. The transverse relaxation times rx were obtained from the dielectric spectra measured for several isotherms as a function of pressure with­ in the SA-phase of CNCN. The activation volume, A#Vj_ = RT (d In = (52 ± 3) cm3/mol is larg­ er than A Vj|, recently derived from the pressure dependence of the longitudinal relaxation times for other substances in the SA-phase. It is concluded that due to steric hindrances made by the cyano groups the molecular rotations around the long axes become strongly slowed down by pressure and the smec­ tic phase disappears 
  Reference    Z. Naturforsch. 56a, 489—4 (2001); received April 23 2001 
  Published    2001 
  Keywords    Liquid Crystals, Smectic A, DTA, Phase Diagram, Dielectric Relaxation, High Pressure 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0489.pdf 
 Identifier    ZNA-2001-56a-0489 
 Volume    56