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'High pressure' in keywords Facet   Publication Year 1999  [X]
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1999[X]
1Author    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 
2Author    Stanislaw Urban, Albert WürflingerRequires cookie*
 Title    High Pressure Dielectric Studies of a Substance with the Smectic A 1 Phase  
 Abstract    The results of dielectric studies of 5-n-hexyl-2-(4'-isothiocyanato)-l,3-dioxane (6DBT) in the smec-tic A, phase at pressures up to 150 MPa and temperatures up to 340 K are presented. The low frequen-cy relaxation time T\\ (/?, T) yields the activation volume A # V|| = RT(d ln Tjj/9/>) r and activation enthal-py A # //jj = R(d ln T||/37) p . The calculated values of these parameters are compared with those ob-tained recently for n-octyl-cyanobiphenyl (8CB) forming the smectic A d phase. In the case of 6DBT both these quantities are practically constant, whereas those for 8CB decrease, when going away from the phase transitions isotropic -smectic A] (6DBT) or nematic -smectic A d (8CB). These differences support our earlier conclusion that increase of pressure leads to a breaking of the antiparallel associa-tions of cyanobiphenyl molecules in the smectic as well as in the nematic phases. 
  Reference    Z. Naturforsch. 54a, 455—458 (1999); received July 12 1999 
  Published    1999 
  Keywords    Liquid Crystal; Smectic A, Dielectric Properties, High Pressure 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0455.pdf 
 Identifier    ZNA-1999-54a-0455 
 Volume    54 
3Author    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 
4Author    Phineus Markwick, Stanislaw Urban, Albert WürflingerRequires cookie*
 Title    High Pressure Dielectric Studies of 8CB in the Isotropic, Nematic, and Smectic A Phases  
 Abstract    The static and complex permittivity of 4-n-octyl-4'-cyanobiphenyl (8CB) has been measured for the isotropic, nematic and smectic A phases as functions of temperature and pressure. The ranges of 297 -361 K, 0.1 -220 MPa, and 0.1 -13 MHz, were covered. Only the parallel component of the complex permittivity, £*(/) = e'(f) — ie"(f), was measured. The relaxation times T||(p, T) as well as ris(p, T) were analysed at constant temperature, pressure and volumes yielding the activation volume, A ¥ V(T), activation enthalpy A^H(p), and activation energy lyU(V), respectively. All activation parameters calculated for the smectic A phase of 8CB are smaller than those obtained for the nematic phase. The activation energy constitutes approximately half of the activation enthalpy value in all three phases studied. The pressure study allowed to calculate the pressure dependence of the retardation factor g\\(p, T), from which the nematic potential q(p,T) can be derived. Using the relationships between g\\ and q/RT proposed by Kalmykov and Coffey, the order parameter (Piip, T)) was calculated as a function of pressure. 
  Reference    Z. Naturforsch. 54a, 275—280 (1999); received March 13 1999 
  Published    1999 
  Keywords    Liquid Crystals, 8CB, High Pressure, Dielectric, Thermodynamics, Order Parameter 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0275.pdf 
 Identifier    ZNA-1999-54a-0275 
 Volume    54 
5Author    S. UrbanRequires cookie*
 Title    Dielectric Studies of 4-w-Hexyloxy-4'-Cyanobiphenyl (60CB) at Elevated Pressure  
 Abstract    The principal dielectric permittivity components in the nematic phase of 4-rc-hexyloxy-4'-cyanobiph-enyl (60CB) were measured as functions of temperature at ambient pressure and as functions of pres-sure up to 100 MPa at several constant temperatures. The dielectric anisotropy is analized in the frame of the Maier-Meier equations. The pressure dependence of the order parameter is deduced. Preliminary results for the activation volume and activation enthalpy from the pressure and temperature dependenc-es of the longitudinal relaxation times are obtained. 
  Reference    Z. Naturforsch. 54a, 365—369 (1999); received March 29 1999 
  Published    1999 
  Keywords    Nematic Liquid Crystal, 60CB, Dielectric Anisotropy, Order Parameter, High Pressure 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0365.pdf 
 Identifier    ZNA-1999-54a-0365 
 Volume    54