Go toArchive
Browse byFacets
Bookbag ( 0 )
'High pressure' in keywords
Results  33 Items
Sorted by   
Publication Year
2001 (3)
2000 (2)
1999 (5)
1998 (3)
1997 (1)
1995 (5)
1994 (1)
1993 (1)
1992 (2)
1991 (1)
21Author    T. Brückert, D. Büsing, A. Würflinger, S. UrbanRequires cookie*
 Abstract    h e r m a l A n a ly s is (D T A) a n d D ie le c tr ic S tu d ie s o f 4 -(tra n s -4 -H e p ty l-C y c lo h e x y l) -b e n z o n itr ile (7 P C H) u n d e r H ig h P r e s s u r e With the aid of DTA the phase diagram of 4-(trans-4-heptyl-cyclohexyl)-benzonitrile, 7PCH, was redetermined. Dielectric studies on the static and complex permittivity have been performed on 7PCH in the pressure range 0.1 -220 MPa, the frequency range 1 kHz-13 MHz and the temperature range 290-380 K. For the slow relaxation process in the nematic phase, characterized by the relaxa­ tion time Tjj , we have calculated the activation volume, A* V u, of about 80 to 60 cm3/mol (decreasing with increasing temperature), and the activation enthalpy, A *Hn, of approximately 70 kJ/mol. The isochoric activation energy, A* Un, amounts to about 36 kJ/mol. The pressure dependence of A * Hu is less pronounced compared with previous findings for 5PCH and 7CB. Estimates of t 0 (extrapo­ lated from the relaxation time in the isotropic phase) allow the calculation of the retardation factor gu = Tn/t0 that is analysed in terms of theories of Martin-Meier-Saupe and Coffey in order to evalu­ ate the nematic potential q. Using data for the order parameter 5 from NMR studies it was possible to determine the strength of the interaction potential in the nematic phase and to check the relation q~S which is valid at p = const., but not at V= const. The results are compared with recent findings for other homologous series. 
  Reference    Z. Naturforsch. 50a, 977—983 (1995); received August 25 1995 
  Published    1995 
  Keywords    Dielectric Relaxation, High Pressure, Liquid Crystals, Activation Parameters, Phase Transitions 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0977.pdf 
 Identifier    ZNA-1995-50a-0977 
 Volume    50 
22Author    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 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0739.pdf 
 Identifier    ZNA-1997-52a-0739 
 Volume    52 
23Author    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 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0275.pdf 
 Identifier    ZNA-1999-54a-0275 
 Volume    54 
24Author    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 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0365.pdf 
 Identifier    ZNA-1999-54a-0365 
 Volume    54 
25Author    A. Würflinger, M. Sandmann, W. WeissflogRequires cookie*
 Title    PVT Measurements on 3-Cyanobenzyl 2,5-bis(4-/i-octyloxybenzoyl- oxy)benzoate up to 250 MPa and 423 K  
 Abstract    P, V m , T data have been measured for the nematic and isotropic phases of 3-cyanobenzyl 2,5-bis (4-n-octyloxybenzoyloxy)benzoate between 273 and 423 K and up to 250 MPa. The volume changes accompanying the crystal -nematic and nematic -isotropic transitions have been determined. The cor-responding enthalpy changes have been calculated using the Clausius-Clapeyron equation. The p, V m , T data enable also to estimate the volume entropy for the nematic-isotropic transition. It is found that the configurational part of the transition entropy amounts to 80%, this portion being distinctly larger than found in previous studies for conventional rod-like liquid crystals. 
  Reference    Z. Naturforsch. 55a, 823—827 (2000); received July 17 2000 
  Published    2000 
  Keywords    Aryl-branched Liquid Crystals, High Pressure, pVT\ Phase Transitions, Thermodynamics 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0823.pdf 
 Identifier    ZNA-2000-55a-0823 
 Volume    55 
26Author    A. Wiirflinger, W. WeissflogRequires cookie*
 Title    DTA and p VT Measurements on 4-cyanobenzyI-5- (4-n-octyloxybenzoyloxy)-2-undecyloxybenzoate up to 250 MPa and 383 K  
 Abstract    The phase diagram of 4-cyanobenzyl-5-(4-«-octyloxybenzoyloxy)-2-undecyloxybenzoate (4CNOUB) has been established with differential thermal analysis (DTA). The pressure range for the smectic A phase is limited, resulting in a triple point at 165 MPa and 378.26 K. p, Vm, T data have been measured for the smectic and istotropic phases of 4CNOUB between 243 and 383 K and up to 250 MPa. The vol-ume changes accompanying the crystal -smectic and scmectic -isotropic transitions have been deter-mined. The corresponding enthalpy changes have been calculated using the Clausius-Clapeyron equa-tion. The p, Km, 7 data enable also to estimate the volume entropy for the smectic -isotropic transition and the volume dependence of the clearing temperature. 
  Reference    Z. Naturforsch. 55a, 936—940 (2000); received September 15 2000 
  Published    2000 
  Keywords    Aryl-branched Liquid Crystals, High Pressure, pVT\ Phase Transitions, Thermodynamics 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0936.pdf 
 Identifier    ZNA-2000-55a-0936 
 Volume    55 
27Author    Hk Müller-Buschbaum, H. PauschRequires cookie*
 Title    Über eine neue Präparationstechnik in der Feststoffchemie, II Hochdruck-Hochtemperatursynthesen mit C02 -Laser A New Preparative Technique in Solid State Chemistry, II High Pressure -High Temperature Reactions with CCVLasers  
 Abstract    A new technique to realize solid state reactions under high oxygen pressure is reported. This method is based on the use of CC>2-Laser radiation in combination with autoclave technique. The experimental set-up is described. 
  Reference    Z. Naturforsch. 34b, 375—377 (1979); eingegangen am 20. November 1978 
  Published    1979 
  Keywords    Solid State Chemistry, CC>2-Laser, High Pressure, High Temperature 
  Similar Items    Find
 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-0375.pdf 
 Identifier    ZNB-1979-34b-0375 
 Volume    34 
28Author    Rainer Jaenicke, Hans-Dietrich Liidemann, Gerhard SchmidRequires cookie*
 Title    Pressure, Temperature and pH Dependence of the Absorption Spectrum of Reduced Nicotinamide Adenine Dinucleotide  
 Abstract    Enzymological studies at high hydrostatic pressure generally involve temperature, pH and pressure as variables, owing to the effect of adiabatic compression and the ionization volume o f the buffer system. In the case of N AD dependent oxidoreductases this implies that the extinction coefficient o f the coenzyme may be affected by p, T and pH, apart from the spectral change accompanying the redox reaction. Measurements o f the pressure dependence of the absorbance of N AD H show a slight red shift and a 1% decrease (3% increase) o f the absorbance at 339 nm (360 nm) at 2 kbar. The pH depen­ dence at the given wavelengths amounts to —(2.4 ± 0.1)% per pH unit (25 °C), while the intrinsic temperature effect (after correction for thermal expansion) is o f the order o f -0.2% per degree (2 0 -3 0 °C). Applying buffers with negligible ionization volume, 366 nm is the optimum wavelength for high pressure studies up to 2 kbar because here the pressure dependent spectral changes o f the N ADH absorption vanish. 
  Reference    Z. Naturforsch. 36c, 84—8 (1981); received October 9 1980 
  Published    1981 
  Keywords    Absorption, Dehydrogenases, High Pressure, NADH, Oxidoreductases, pH Dependence, Tem­ perature Dependence 
  Similar Items    Find
 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0084.pdf 
 Identifier    ZNC-1981-36c-0084 
 Volume    36 
29Author    S. A. Lifits, S. I. Anisimov, J. Meyer-Ter-VehnRequires cookie*
 Title    Shock Waves produced by Impulsive Load: Equation of State Effects  
 Abstract    A numerical study of the flow after impulsive load of a plane material surface is carried out. It is shown that the flow is asymptotically self-similar provided one can neglect the cold components in the equation of state. In this case the effective exponent s(r) = d ln(Xs)/d ln(r), derived from the shock trajectory X s (t) does not depend on the initial pressure pulse and approaches the exponent a of the self-similar problem for time t-* oo. For equations of state containing a cold pressure term, s (r) is larger than a and changes non-monotonically with time. Some features of the flow related to the presence of cold components in pressure and internal energy are discussed. 
  Reference    Z. Naturforsch. 47a, 453—459 (1992); received September 9 1991 
  Published    1992 
  Keywords    Shock wave, Impulsive load, Equation-of-state, High pressure, Self-similar flow 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0453.pdf 
 Identifier    ZNA-1992-47a-0453 
 Volume    47 
30Author    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 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0626.pdf 
 Identifier    ZNA-2001-56a-0626 
 Volume    56 
31Author    Yukihiro Yoshimura, Seiji Sawamura, Yoshihiro TaniguchiRequires cookie*
 Abstract    f fe c ts o f P r e s s u r e , T e m p e r a tu r e , a n d C o n c e n tr a tio n o n th e V is c o s ity o f A q u e o u s A m m o n iu m B ro m id e S o lu tio n Dedicated to Prof. Hitoshi Ohtaki on the occasion of his 60th birthday The viscosity of aqueous ammonium bromide solutions is measured at 0.1-1.0 mol kg-1, 278.2-323.2 K, and 0.1-375 MPa, using a high-pressure rolling-ball viscometer. The activation energy (£v) for viscous flow and Jones-Dole's B coefficient are estimated. Ev against pressure yields a concave curve with a minimum and B yields a convex one with a maximum. These phenomena are attributed to pressure, temperature, and concentration effects on the water-structure. 
  Reference    Z. Naturforsch. 50a, 316—322 (1995); received December 14 1994 
  Published    1995 
  Keywords    Viscosity, High pressure, Ammonium bromide, Activation energy, Jones-Dole's B coef­ ficient 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0316.pdf 
 Identifier    ZNA-1995-50a-0316 
 Volume    50 
32Author    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 
  Similar Items    Find
 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0489.pdf 
 Identifier    ZNA-2001-56a-0489 
 Volume    56 
33Author    J. Paul, E. V. Goldammer, H. R. WenzelRequires cookie*
 Title    Pressure Induced Structural Fluctuations in Hemoglobin, Studied by EPR-Spectroscopy  
 Abstract    A quartz based cavity for pressure dependent EPR measurements on liquid samples allowing pressures up to 0.6GPa was constructed. First investigations with this setup were done on spin labeled horse hemoglobin derivatives both in ferric and ferrous state of oxidation. The second derivative EPR spectra show changes of the label's mobility, which are not correlated with spin state changes of the Fe-porphyrin complex, but which point out structural fluctuations inside the globin protein matrices. 
  Reference    Z. Naturforsch. 43c, 162—166 (1988); received December 22 1987 
  Published    1988 
  Keywords    High-Pressure, Electron Paramagnetic Resonance, Second Harmonic Detection, Liquid Systems, Hemo-Proteins, Structural Fluctuation, Ligand Binding 
  Similar Items    Find
 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0162.pdf 
 Identifier    ZNC-1988-43c-0162 
 Volume    43