摘要:

AbstractThe electroclinic effect, a kind of inverse piezoelectric effect, is studied in the smectic A phase of several homologous liquid crystal compounds. The induced tilt/applied field ratio θ/Eis found to increase with increasing length of the alkyl chain whereas the coupling constantk=Pθ/θ between induced tilt and induced polarization decreases with increasing chain length. The measurements allow the determination of the tilt controlling susceptibility coefficient of the smectic A phase, which is found to decrease considerably with increasing alkyl chain leng

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950701

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractA new method and apparatus are described for the determination of concentration in liquid mixtures through the measurement of their thermal effusivity. The inverse photopyroelectric method (IPPE) implies the front illumination of a thin pyroelectric sensor the rear side of which is brought into the intimate thermal contact with the sample. The feasibility of this novel technique is demonstrated with ethanol‐water mixtures. Good agreement between the experiment and theory has been obtaine

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950702

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractIn slightly acidic solutions of Ag+and carboxy‐methane‐thiol (CMT) or carboxy‐ethane‐thiol (CET), aggregates are formed whose absorption spectrum is significantly different from that of the monomeric silver‐carboxy‐alkane‐thiols. The build‐up of the aggregates occurs slowly. They develop a band at 335 nm (AgCMT) or 355 nm (AgCET), and simultaneously, acquire fluorescence. Silver is produced upon the photolysis of the aggregates. A very small amount of silver atoms deposited on the aggregates is sufficient to quench the fluorescence substantially. Both the absorption and fluorescence bands are blue‐shifted as the aggregates become smaller during photolysis or dissolution in alkaline solution. The aggregates are proposed to have semiconductor‐like ionic planes separated from each other by the organic groups. Electron microscopy shows that the aggregates are partly crystalline and have a size of about 25 Å when they are freshly prepared. The crystallinity increases and the structure changes upon aging for several days.—When Ag+is reduced by NaBH4in the presence of carboxy‐alkane‐thiols, stable silver aggregates of different sizes are formed. The absorption bands and chemical behaviour of some of the aggregates resemble those of oligomeric silver clusters investigated previously. The stability of the clusters is explained in terms of “pre‐complexation” of silver

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950703

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rates for the consecutive acid hydrolysis of ditert‐butylsuccinate were measured in a series of an aqueous dipolar aprotic solvent, namely, acetone. The observed rates of the two steps of the reaction were analysed into four separate terms due to the unimolecular (AAL1) and bimolecular (AAC2) mechanisms. These rates were correlated with the measured acidity functionH0of the medium, where linear relationships exist at lower acetone contents for the unimolecular rate constants (k′I1&k′II1). The bimolecular rate constants (k′I2&k′II2), however, follow a non‐linear trend indicating the operation of the AAC2 mechanism. The activation parameters and the rate‐acidity function relationships were computed and discussed as evidences of mechanistic pathway and solvation effects involved in

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950704

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe electrochemical behaviour of the Au‐rotating disc electrode (rde) in the Fe(CN)3‐/4‐6redox system in pure water and water‐glycerol mixed solvents was studied. Using standard potentiostatic technique, the kinetic parameters controlling the anodic and cathodic processes were derived. The effect of the speed of rotation of the rde, the temperature, and the scan rate on the current‐potential characteristics of the system was investigated. The thermodynamic parameters of the Fe(CN)3‐/4‐6in glycerol‐water mixed solvent were calculated. It turns out that the electrode processes are mass transport controlled. The presence of glycerol retards the charge transfer process and enhances the mass transport effects. The calculated thermodynamic data revealed that the rate of the anodic reaction is enthalpy controlled whereas that of the cathodic one is ent

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950705

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe miscibility gap between n‐butanol and water can be closed by the addition of transition metal perchlorates. As transition metal ions we used Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+. All phase diagrams are of the same shape when the salt contains a divalent cation, while the equilibrium curve in the Fe3+system encloses a one third smaller region of the phase triangle. UV/VIS‐spectra of Ni(ClO4)2in butanol/water show that nickel ions are preferentially hydrated. These facts lead to the conclusion that the closing of the miscibility gap is only due to butanol/perchlorate interactions. The finding that the change of the transition metal does not affect the behaviour of the system is corroborated by measurements of the density and the transport properties electrical conductivity and kinematic viscosity. All three properties depend on the concentration, but not on the nature of the salt. Investigations of the phase diagrams at lower temperatures show a second region with two coexisting liquid phases at higher salt concentrations. This region becomes smaller with increasing temperature while the miscibility gap in the region with lower salt contents grows with increasing temperat

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950706

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractQuaternary solutions of the surfactant Tetradecyldimethylaminoxid (C14H29N(CH3)2O, TDMAO) in D2O, equimolar concentrations of Decane and some cosurfactant Hexanol show at low concentration the phenomenon of iridescence. The colour of the backscattered light changes from red to blue with increasing surfactant concentration. Small‐angle neutron diffraction (SANS) patterns were recorded for different concentrations between 27 and 584 mM TDMAO. It is shown that the iridescent colours are due to Bragg reflections of visible light from lamellar layers. By simulation based on a one‐dimensional crystal model the thickness of the bilayers and the lattice parameter of the liquid crystalline structure could be determined. At higher concentrations the samples showed a pronounced anisotropic SANS‐pattern, the origin of which is related to the procedure of filling the solution into the flat, disklike quartz cells of path length

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950707

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractMolar excess enthalpies (HE) and molar excess volumes (VE) of the liquid mixture Propan‐1‐ol (PrOH) + Triethylamine (TEA) + n‐Heptane have been measured by flow calorimetry and the vibrating tube technique respectively. Data of the three binary systems have also been obtained. The excess properties are dominated by strong hydrogen bondings due to the self‐association of PrOH and the association of PrOH with TEA. The third component, heptane, serves mainly as an inert diluting solvent.HEandVEare positive for PrOH + heptane and also for TEA + heptane to a much smaller extent. Strongly negative values of bothHEandVEhave been obtained for PrOH + TEA. The values obtained for the ternary system lie in between these extreme cases showing certain compositions whereHEandVEvanish.—An extended version of the so‐called ERAS model has been used for describingHEandVEof the complete ternary system. The parameters adjusted to the binary data reveal that the hydrogen bonding enthalpies and volumes between PrOH and TEA are distinctly stronger than between self‐associating PrOH molecules. In addition the widely applied NRTL‐model has also been used for describingHEof the ternary systems.VE, however, can not be calculated with

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950708

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractBy using differential scanning calorimetry and neutron small‐angle scattering, the effect of the local anaesthetic tetracaine on the temperature and pressure dependent phase behaviour of model biomembrane systems, such as pure and cholesterol—containing 1, 2‐dimyristoyl‐phosphatidylcholine bilayers, has been investigated. The results provide insight into the thermodynamic and structural consequences of the incorporation of the anaesthetic into the membranes and might thus help in understanding the molecular mechanisms underlying the pharmacological action of local anaesthetics and the antagonistic effect of pressure against anaesthesia, which has been observed in vivo. Furthermore, as tetracaine can be viewed as a model system for amphiphilic molecules, knowledge of its concentration, temperature and pressure dependent phase behaviour helps in understanding the general physico‐chemical action of amphiphilic molecules on

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950709

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe electrochemical oxidation of hydrogen on a platinum anode in the presence of copper ions exhibits under galvanostatic conditions kinetic oscillations due to periodic poisoning and activation transitions of the electrode by underpotential deposition and dissolution of a passivating Cu monolayer In the presence of chloride ions a transition to chaos from a stationary state via a Hopf bifurcation and a sequence of period doublings (Feigenbaum scenario) was observed upon increase of the current density. Further change of this control parameter caused a transition to another qualitatively different chaotic state through an interior crisis. Near the other end of the oscillatory region, this state evolved into periodic mixed‐mode behaviou

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950710

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY