| 2 | Author
| A. Heinrich-Schramm, W. E. Price, H.-D Lüdemann | Requires cookie* | | Title
| T  | | | Abstract
| h e In flu e n c e o f D ip o le -D ip o le I n te r a c tio n a n d H y d r o g e n B o n d in g U p o n T r a n s la tio n a l D iffu s iv ity in S im p le F lu id s Self-diffusion coefficients of dimethylether have been measured as a function of temperature (185-458 K) and pressure (up to 200 MPa) by pulse-gradient field spin-echo NMR. Calculated activation volumes (AV*) fall from 15 (10-6 m3/mole) at the highest temperature to 7 (10~6 m3/mole) at the lowest. This trend is in keeping with values for other non-associating liquids. Comparison with self diffusion data for propane and ethanol reveals that the translational diffusivity in dimethylether is influenced by the substance's modest dipole moment (1.3 Debye). The effect is small but measur able and becomes more pronounced at lower temperatures. S e lf-D iffu s io n in C o m p re s s e d D im e th y le th e r : | | |
Reference
| Z. Naturforsch. 50a, 145—148 (1995); received October 5 1994 | | |
Published
| 1995 | | |
Keywords
| Dimethylether, Diffusion, High Pressure | | |
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| default:Reihe_A/50/ZNA-1995-50a-0145.pdf | | | Identifier
| ZNA-1995-50a-0145 | | | Volume
| 50 | |
3 | Author
| M. Sandmann, F. Hamann, A. Würflinger | Requires 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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| default:Reihe_A/54/ZNA-1999-54a-0281.pdf | | | Identifier
| ZNA-1999-54a-0281 | | | Volume
| 54 | |
4 | Author
| Albert Würflinger, M. Massalska-Arodż3, S. Urbanb, W. Weissflogc, S. Emstc | Requires 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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| default:Reihe_A/56/ZNA-2001-56a-0658.pdf | | | Identifier
| ZNA-2001-56a-0658 | | | Volume
| 56 | |
5 | Author
| J. R., D. B., F. K. | Requires cookie* | | Title
| High Pressure Reactions, IX 1 Isomerizations at High Pressures  | | | Abstract
| Cyclooctatetraene dimerises at high pres sure (12 Kbar, 20 °C) to the isomers 2 and 3. At 120 °C compound 2 isomerises quanti tatively to compound 3. The conversion rate of Hexamethyldewarbenzene to Hexamethyl-benzene at high pressures depends on kind of solvent, whereas the influence of tempera ture is small in the range between 2 0 ° and ' 80 °C. | | |
Reference
| (Z. Naturforsch. 30b, 290 [1975]; eingegangen am 17. Oktober 1974) | | |
Published
| 1975 | | |
Keywords
| High Pressure, Cyclooctatetraene, Dimerisation, Hexamethyldewarbenzene, Isomerization | | |
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| default:Reihe_B/30/ZNB-1975-30b-0290_n.pdf | | | Identifier
| ZNB-1975-30b-0290_n | | | Volume
| 30 | |
6 | Author
| Rolf-Rüdiger Krüger, W. Alter, Abriel | Requires cookie* | | Title
| Über das Hochdruckverhalten von Gips On the Behaviour of Gypsum under High Pressure  | | | Abstract
| The decom position o f gypsum (dehydration) was studied in the pressure range 7 .5 -6 0 kbar and the temperature range 7 5 -4 0 0 °C using a belt type apparatus. Surprisingly, gypsum is rather stable even at pressures greater than 20 kbar contradicting the results o f a calculation o f the space requirement o f the competing phases (A I I -C a S 0 4 + H-,0; Hemihydrate + H20). Only when rising the temperature, as the most important thermodynamic variable for this reaction, the kinetically controlled decomposition starts. N o acceleration o f the dehydration process under shear stress (simple squeezer device) could be detected due to the limited (not geological) time. | | |
Reference
| Z. Naturforsch. 45b, 1221—1226 (1990); eingegangen am 27. Februar 1990 | | |
Published
| 1990 | | |
Keywords
| Gypsum, Hydrates, High-Pressure, D ecom position | | |
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| default:Reihe_B/45/ZNB-1990-45b-1221.pdf | | | Identifier
| ZNB-1990-45b-1221 | | | Volume
| 45 | |
7 | Author
| H. Einz, Jürgen Beister, K. Arl Syassen, Jürgen Klein | Requires cookie* | | Title
| Phase Transition of N a3As under Pressure  | | | Abstract
| We have investigated the high pressure behaviour of N a3As by powder X-ray diffraction. At 3.6 G Pa the material undergoes a reversible phase transition from the N a3As structure (P 6 3/ mmc, a = 487.4(8) pm, c = 851.5(20) pm, Z = 2, at 3.6 G Pa) to the Li3Bi structure type (Fm 3m , a = 683.5(15) pm, Z = 4, at 3.6 GaP). The equation of states is given for the pressure range up to 26 GPa. Results are discussed with respect to structural properties of related A3BV-compounds. | | |
Reference
| Z. Naturforsch. 45b, 1388—1392 (1990); received M arch 7 1990 | | |
Published
| 1990 | | |
Keywords
| High Pressure, Crystal Structure, Phase Transition | | |
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| default:Reihe_B/45/ZNB-1990-45b-1388.pdf | | | Identifier
| ZNB-1990-45b-1388 | | | Volume
| 45 | |
8 | Author
| Oliver Schilke, EberhardH. Ohaus, H. Arro Lentz, JeongR. Kim | Requires cookie* | | Title
| HPTLC-Analyse von Ginsenosiden zur Bewertung von Ginseng-Extraktionen mit Methanol-Wasser, Wasser oder Ammoniak HPTLC Analyses o f Ginsenosides for the Evaluation of Ginseng Extractions with M ethanol-W ater, W ater or Am m onia  | | | Abstract
| Korean Ginseng roots were extracted with m ethanol-w ater, water and liquid and supercriti cal ammonia. The yields of the extracts by different methods are reported. The extracts were analyzed by high-performance thin-layer chrom atography. Retention value factors of ginsen osides are tabellized. The absolute yields have been measured in mg ginsenoside per g ginseng root for the used standard ginsenosides. Formally the am m onia extraction at 334 K and 26 bar is found to be favourable. The supercritical condition of 418 K and 130 bar leads to a decom position of the ginsenosides. Possibilities of fractionation by different solvents or different temperatures are indicated, but attem pts are still required to get fractions o f several extraction agents. | | |
Reference
| Z. Naturforsch. 46b, 829—834 (1991); eingegangen am 17. Dezember 1990 | | |
Published
| 1991 | | |
Keywords
| Ginsenoside, Extraction, H PTLC Analysis, High Pressure | | |
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| default:Reihe_B/46/ZNB-1991-46b-0829.pdf | | | Identifier
| ZNB-1991-46b-0829 | | | Volume
| 46 | |
10 | Author
| Heinrich-Schramm, W. E. Price, H.-D Lüdemann | Requires cookie* | | Title
| A  | | | Abstract
| Self-diffusion in ethanol/hexane and dimethylether/hexane mixtures of various compositions has been measured at 215-350 K and up to 200 MPa. Qualitative analysis of the results indicates that, as expected, hydrogen bonding retards the self-diffusion of ethanol in the mixture, especially at the low temperatures. Dimethylether shows a slight effect of dipole-dipole interactions on the self-diffu sion, as seen by a higher AE* value than for the alkane. However there is no significant difference in the pressure dependence for both mixtures. This is shown by considering the ratio of the two diffusion coefficients, which suggests that, contrary to what is observed for pure alcohols, pressure has little effect upon the hydrogen bonding of ethanol in the mixture. In additon, there is surprisingly little concentration dependence on the ratios for either mixture. | | |
Reference
| Z. Naturforsch. 50a, 149—154 (1995); received October 5 1994 | | |
Published
| 1995 | | |
Keywords
| Binary mixtures, Self diffusion, High pressure | | |
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| default:Reihe_A/50/ZNA-1995-50a-0149.pdf | | | Identifier
| ZNA-1995-50a-0149 | | | Volume
| 50 | |
11 | Author
| Z. Naturforsch | Requires cookie* | | Title
|  | | | Abstract
| The pressure-dependence of the dielectric anisotropy, Ae = e0||— e0±, of two nematogens, n-pentyl-and n-hexyl-cyanobiphenyl (5CB and 6CB) has been measured at constant temperature. For this purpose a high pressure chamber made of non-magnetic materials was constructed, allowing for the orientation of the samples by a magnetic field. The pressure dependencies of Aex were analyzed in the frame of the Maier-Meier equations for the principal permittivity components in the nematic phase. It was found that the relation between Ae and the order parameter S is not properly described by these equations. The Kirkwood correlation factor calculated on the basis of the present results and the Maier-Meier equations is smaller than 0.5, whereas it increases to a more realistic value (~0.7) if the electronic polarization is incorporated in the equations. P r e s s u r e D e p e n d e n c e o f th e D ie le c tric A n is o tr o p y o f 5 C B a n d 6 C B | | |
Reference
| Z. Naturforsch. 50a, 826—830 (1995); received April 28 1995 | | |
Published
| 1995 | | |
Keywords
| Nematic liquid crystals, Cyanobiphenyls, High pressure, Dielectric anisotropy | | |
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| default:Reihe_A/50/ZNA-1995-50a-0826.pdf | | | Identifier
| ZNA-1995-50a-0826 | | | Volume
| 50 | |
12 | Author
| A. Wiirflinger | Requires cookie* | | Title
| Nematic Potential and Order Parameter Determined from Dielectric Measurements  | | | Abstract
| The Maier-Saupe theory is employed in order to calculate order parameters S from the nematic po-tential q. It is found that one of the basic assumptions of the Maier-Saupe theory, q ~S, is approximate-ly fulfilled. The relation between q and S is analysed for various state changes. Previously reported find-ings for 7 PCH that q ~S, not fulfilled along isochoric changes, can be explained by taking into account the pressure and temperature dependences of q. The procedure described in this paper allows to treat experimental data for the nematic potential in a unique way, without being affected by inadequacies of experimentally determined order parameters. | | |
Reference
| Z. Naturforsch. 53a, 141—144 (1998); received February 11 1998 | | |
Published
| 1998 | | |
Keywords
| Liquid Crystals, High Pressure, Nematic Potential, Dielectric Relaxation | | |
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| default:Reihe_A/53/ZNA-1998-53a-0141.pdf | | | Identifier
| ZNA-1998-53a-0141 | | | Volume
| 53 | |
13 | 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 | |
14 | 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 | |
15 | Author
| Stanislaw Urban, Albert Würflinger | Requires 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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| default:Reihe_A/54/ZNA-1999-54a-0455.pdf | | | Identifier
| ZNA-1999-54a-0455 | | | Volume
| 54 | |
18 | Author
| SeymourSteven Brody, Karel Heremans | Requires cookie* | | Title
| Pressure Induced Shifts in Spectral Properties of Pigment-Protein Complexes and Photosynthetic Organisms  | | | Abstract
| Application o f elevated pressure (up to 1200 bars) results in a bathochrom ic shift o f the absorption bands o f photosynthetic pigments. The photosynthetic system s studied include: photosystem I particles, chloroplasts, acetone extracts o f chloroplasts, A U T particles and light harvesting particles o f Rh. sphaeroides, light harvesting particles o f R26. Sim ilar spectral changes are observed in all systems. The spectral shifts appear to be associated w ith pressure-induced changes in the local electric fields o f the pigm ents, rather than changes in the index o f refraction o f the solvent. | | |
Reference
| Z. Naturforsch. 39c, 1104 (1984); received June 18 1984 | | |
Published
| 1984 | | |
Keywords
| Photosynthesis, Chlorophyll, High Pressure, Reaction Centers, C hlorophyll-Protein C om plexes | | |
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| default:Reihe_C/39/ZNC-1984-39c-1104.pdf | | | Identifier
| ZNC-1984-39c-1104 | | | Volume
| 39 | |
19 | Author
| H. G. Kreul, R. Waldinger, A. Würflinger | Requires 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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| default:Reihe_A/47/ZNA-1992-47a-1127.pdf | | | Identifier
| ZNA-1992-47a-1127 | | | Volume
| 47 | |
20 | Author
| J. Reuter, T. Brückert, A. Würflinger | Requires 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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| default:Reihe_A/48/ZNA-1993-48a-0705.pdf | | | Identifier
| ZNA-1993-48a-0705 | | | Volume
| 48 | |
|