ISSN:0005-9021    

DOI:10.1002/bbpc.19961000103

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

年代:1996

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000102

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

年代:1996

数据来源: WILEY

摘要:

AbstractOn increasing concentration in highly diluted aqueous solutions of pseudoisocyanine dyes an intensive absorption band of extremely small half‐width (Scheibe band) occurs which is attributed to the formation of dye aggregates (Scheibe or J‐aggregates). By polarizing microscopy it is shown that aqueous solutions of pseudoisocyanine diethylchloride at low temperatures and at concentrationsc>0.2 wt% become birefringent and exhibit a Schlieren texture characteristic for nematic liquid crystals. Above a certain clearing temperatureTcthe solution becomes optically isotropic during a discontinuous phase transition as shown by DSC. The Scheibe band vanishes at temperatures some degrees aboveTc. The phase behaviour is displayed in terms of aT‐c diagram. The aggregation numbers have been determined spectroscopically to about 40 to 50 only slightly increasing belowTc. Obviously, the Scheibe aggregates exhibit a long‐range orientational order even at high dilution typically for a nematic lyotropic liquid crystal. The phase diagram indicates that on increasing temperatures the orientational long‐range order vanishes first before the Scheibe aggregates will be thermically d

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000104

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe aggregation behavior of pseudoisocyanine chloride (= PIC) (1,1′‐diethyl‐2,2′‐cyanine chloride) in dilute aqueous solutions was observed up to 375 MPa by absorption spectroscopy. From the pressure dependence of the dimerization constant the change in volume associated with the dimerization, ΔVD= −12.6 cm3·mole−1, could be obtained. By means of this value of ΔVDthe interplanar spacing of the quinoline rings in the dimer was estimated to 3.0·10−8cm. At higher concentrations the pressure dependence of the pressure‐induced absorption‐band (Scheibeband) yields the volume contraction (ΔVS) caused by the aggregation. Evaluation of ΔVS/ ΔVDallows a rough determination of the mean aggregation numbernof monomer units per Scheibe‐aggregate.nincreases with increasing concentration of PIC. The v

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000105

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

年代:1996

数据来源: WILEY

摘要:

AbstractAthermal Monte Carlo simulations for a mixed monolayer built up from flexible molecules with different chain lengths have been carried out within a cubic lattice model. Only excluded volume interactions are taken into account. The number of chain segments per molecule, the head density, and the mole fraction of each component are varied. It is the aim of the work to investigate the orientational order in such mixtures. The calculated correlation lengths and snapshots did not show any evidence for demixing. In order to understand the effect of mixing on ordering some additional properties of the system have been investigated. Results demonstrating the influence of the mole fraction and chain length on the orientational order parameter, the end‐end distance, the end‐end projection, and the density profiles are presented. These quantities exhibit deviations from an ideal mixing rule. The deviations get stronger with increasing relative chain length difference. The shorter chains do not align in the local environment of long cha

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000106

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

年代:1996

数据来源: WILEY

摘要:

AbstractWe report on shear viscosity data near the upper consolute point of the ionic system tetrabutylammonium picrate+1‐tridecanol (Tc= 341.845 K) which shows a large mean‐field region in its static critical properties with crossover to Ising behavior close to the critical temperature. After suitable assessment of the non‐singular background viscosity we establish that the asymptotic scaling law η ∝ τ−yapplies in the region τ<5 ×10−3, where τ = (T‐Tc)/Tcis the reduced temperature. The value of the exponent is determined to y = 0.0434±0.001 which is close to the current best value for the 3d‐Ising model,y= 0.041. At higher reduced temperatures pronounced deviations from Ising criticality are observed. In agreement with the mean‐field predictiony= 0, the critical contribution is vanishing. This crossover is discussed in the fram

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000107

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe problem of molecular thermal (Pq) polarization estimation in the substances with different forms of aggregation and using different experimental techniques is discussed. It is shown on the base of numerous experimental data analysis thatPqincludes both rotational (Prot) and orientational (Por) components, which may be commensurable in magnitude in gases and gasiform condensed media. The principle of equal distribution of molecules' thermal polarization over their kinetic degrees of freedom is being satisfied, soProtterm should not be neglected. The neglect of this fact on estimation of the molecular dipole moments using the first method of Debye results in √(5/3) or √(4/3) times overestimated dipole moment val

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000108

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

年代:1996

数据来源: WILEY

摘要:

AbstractThin films of chloroauric acid salt of chitosan (CTOAu films) were photolyzed with 253.7 nm light. On irradiating with UV light in air at room temperature, the CTOAu film first became yellow‐blue colored due to the formation of colloidal gold. When irradiation was continued, the irradiated surface of the film finally changed into clear gold mirror. Primary photochemical products are assumed to be gold atom, quaternary ammonium chloride of chitosan and chlorine. With aids of UV‐visible absorption spectroscopy, X‐ray photoelectron spectroscopy, and scanning electron microscopy, aggregation of small gold particles to form colloidal gold and gold metal film has been investigated. It has been found that the aggregation state of small gold particles is controlled by reaction conditions; temperature, evacuation, the amount of chloroauric acid. When the CTOAu film was photolyzed in vacuum at room temperature, the gold particulate film was formed. Irradiation at liquid nitrogen temperature resulted in absorption spectrum characterized by the structureless absorption extending from λ = 400 nm to shorter wavelength. However, an introduction of air after photolysis brought about the development of the broad colloidal absorptio

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000109

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe mechanism of fluorescence quenching through intramolecular electron transfer (ET) was investigated in the dipeptide model compounds DL‐N‐[4‐(diethylamino)alkyl]‐2‐acetylamino‐3‐(1‐naphthyl)propionamides (1) by stationary and time‐resolved fluorescence spectroscopy in non‐polar and polar solvents. An analysis of the observed singlet‐exciplex fluorescence and the biexponential decay of monomer fluorescence established that emission quenching in non‐polar solvents proceeds through the singlet‐exciplex intermediate with a strong charge‐transfer character, and that the quenching rate constant increases with a decrease in free‐energy change for ET (ΔGet) but it is not very sensitive to the variation of methylene chain length in 1. The observations of biexponential emission decay and very weak exciplex emission in polar solvents suggest that a singlet exciplex and/or a solvent‐separated radical ion pair become a key intermediate in the quenching process. The finding that the magnitude of ΔGet, being regarded as a measure of the stability of an intermediate formed, linearly correlates with the logarithm of solvent viscosity is explained in terms of a short‐lived singlet exciplex that serves as a precursor of the radical ion pair intermediate. Thus, solvent viscosity effects on the biexponential emission decay processes of 1 with small ΔGetin protic polar solvents provide a good criterion for the exclusive operation of a singlet‐exciplex mechanism in the case that a short‐lived exciplex and a long‐lived radical ion pair are produced. It was also found that any of activation parameters for ET fluorescence quenching process in acetonitrile is comparable to the corresponding parameter obtained in methylcyclohexane. This finding may present kinetic evidence for the participation of a singlet‐exciplex mechanis

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000110

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

年代:1996

数据来源: WILEY

摘要:

AbstractA pulsed electrochemical deposition technique is developed which allows to produce large amounts of nanocrystalline palladium with very low porosity. By an appropriate choice of the deposition parameters the shape and the size of the crystallites can be varied.

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000111

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

年代:1996

数据来源: WILEY