ISSN:0005-9021    

DOI:10.1002/bbpc.19810851002

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

年代:1981

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851003

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe forces operating in thin liquid films of colloidal dimensions are reviewed. These forces are: Van der Waals (dispersion‐), electrical and steric interactions. A discussion is given on their evaluation in situations of practical interest, including dynamic conditions. The review covers both symmetrical and asymmetrical films. A few examples are given to indicate possible application

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851004

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

年代:1981

数据来源: WILEY

摘要:

AbstractA thermodynamic theory for the treatment of transport phenomena in multiphase and multicomponent systems is presented. Starting point is a field theoretical description of interfacial systems. The interface in its three dimensional structure is described by new thermodynamic variables, namely the structure vectorsakof the componentsk. This offers the possibility to analyse processes related with a change of the three dimensional structure by means of the methods of irreversible thermodynamics. Compared to the well known theory of irreversible processes in single phase and membrane systems there are differences regarding the balance equations for component masses and momentum; additionally a balance equation for the structure vector has to be introduced to treat changes of the interfacial structure. The linear constitutive equations obtained from the production term of the entropy balance equation describe transport processes at every point of a multiphase system.—It is shown that in the interfacial region of multiphase systems there are other processes producing entropy than in the bulk of a single phase system. E. g. in the region of an interface Fickian diffusion is not allowed to occur due to a stability criterion. Instead of this a tensorial transport phenomenon due to the structural change of the interface sets in which is possible only at interfaces. By means of a thermodynamic coupling of this tensorial process with the tensorial momentum transport a thermodynamic explanation and description of the Marangoni‐effect is obtained.—New expressions for entropy producing processes are also derived for generalized chemical reactions and transport of momentum. A discussion of potential interactions between fluxes shows that the same cross‐effects occurring in single phase systems cannot be supposed to occur in an interfacial region roo. This results in new aspects for the thermodynamic explanation of active tr

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851005

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

年代:1981

数据来源: WILEY

摘要:

AbstractAt first a survey of the different types of interfaces: fluid/gas, fluid/fluid, and fluid/solid and their technical applications is given. Following techniques for coating solids with thin liquid filmes are treated and as an example the production of photographic materials is described.

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851006

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

年代:1981

数据来源: WILEY

摘要:

AbstractEllipsometry is an optical non‐destructive method used to examine a surface or a thin film. The principle of measurement is a characteristic change in the state of polarization of elliptic polarized light reflected at a clean or a film‐covered surface. This surface may be on a solid or on a liquid. Normally the evaluation takes place with the aid of a computer. The results are the optical properties of the surface: refractive index and extinction coefficient, or thickness and refractive index of the f

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851007

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe height of a steady state dispersion formed in a vertical vessel increases with the throughput of the disperse phase. Since the cross‐sectional area of the disengaging interface remains constant, the volume rate of coalescence per unit area of the interface must increase as the throughput increases. There are three possible ways in which this may occur:1The films are formed between the drops or bubbles shortly after entering the dispersion and gradually become thinner, due to drainage, as they pass through the dispersion until the critical film thickness is reached when the bubbles coalesce with their homophase. If the disperse phase throughput is increased, so the dispersion height increases to keep the residence time of the bubbles and films between them constant, the critical thickness being reached at the disengaging interface. If there is no change in hold‐up of the disperse phase this model, in its simplest form, infers a linear increase in dispersion height with throughput. It is more likely to apply to gas/liquid foams than liquid/liquid dispersions, since the bubbles in a foam do not move relative to each other and the films remain intact, once formed. This is only true close to the disengaging interface in a liquid/liquid dispersion, as in the bulk there is usually considerable turbulence and relative motion of the drops.2The drops (or bubbles) coalesce together in the dispersion to give larger drops. If the coalescence time remains constant the volume rate of coalescence at the disengaging interface will increase as the drop volume increases. This model also infers an increase in height with throughput since the residence time increases to allow the drops to grow in size.3The coalescence time of drops at the disengaging interface is itself influenced by the dispersion height. Close to this interface is a region in which the drops are packed so closely that forces are transmitted from drop to drop. These forces are mainly gravitational, arising from the net weight of the drops above and partly due to the rate of change of momentum of the freely moving drops as they strike this layer. The coalescence time of a drop in a close‐packed dispersion does in fact decrease as the force pressing on it increases, since the area of the draining film cannot increase as it is constrained by the presence of surrounding drops (as distinct to a free drop for which the coalescence time, τ increases with applied forceF, because the area of the film,Aincreases and hence also the coalescence time according to the approximate equation\documentclass{article}\pagestyle{empty}\begin{document}$$ \tau {\rm = }kA^2 /F $$\end{document}in whichkis constant for a given fluid/liquid system). Thus, if the thickness of the close‐packed layer increases with the disperse phase throughput so will the volume rate of coalescence at the disengaging interface. In addition, some binary coalescence occurs in the turbulent zone and the drops pass from this zone into the close‐packed zone when they have grown in size.The design engineer is interested in the rate at which a foam decays and the steady state height of a dispersion which is continuously produced. The rate of growth of the dispersion is important when the plant is started up or when operating conditions change. Although it is difficult to predict the behaviour of a dispersion from basic principles because of the complex nature of the phenomena involved, it is perhaps possible to predict the behaviour of one phase in its lifetime by observing the behaviour of another phase. For example, the steady state height and rate of growth may be predicted from measurements made on the decaying dispersion. The decay is usually easiest to observe as a sample of the dispersion can be removed from the plant and allowed to settle, or the two phases mixed together in a vessel under appropriate conditions before being allowed to separate.—The volume rate of coalescenceVat the disengaging interface where the disperse phase hold‐up is εiis\documentclass{article}\pagestyle{empty}\begin{document}$$ V = 2\varepsilon _i d_i /3\tau _i $$\end{document}so the coalescence time τimay be obtained if the drop diameterdiis known. The growth in drop diameter,d, with residence timetwithin the dispersion is given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ d = d_0 \exp (t/6\tau _b ) $$\end{document}so the binary coalescence time τbmay be obtained if the initial drop diameterdois known. The determination of coalescence times from batch data is discussed. Mathematical models for predicting the steady state dispersion height and the decay and growth of unsteady state dispersions are applied to recent

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851008

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

年代:1981

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851009

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

年代:1981

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851010

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

年代:1981

数据来源: WILEY

摘要:

AbstractWe have used the “Stopped‐Flow”‐ and the “Continuous Flow”‐methods to investigate the electron‐transfer behaviour of silver‐porphyrin complexes in aqueous and micelle containing solutions. Using IrCl62‐or Os(dipy)33+as the electron acceptor compound and silver(II) complexes of tetraphenylporphyrin tetrasulfonic acid (TPPTS), protoporphyrin (PP) or mesoporphyrin (MP) as the electron donor, second‐order rate constants between 104M−1s−1and 1010M−1s−1could be measured.—In aqueous solutions all three porphyrin complexes showed a complex kinetic behaviour because of dimerisation or the formation of higher aggregates. Only Ag(II)TPPTS was monomeric at low ionic strength.—In the presence of surface active substances such as sodiumdodecylsulfate (SDS), dodecyltrimethylammonium chloride (DTAC) or cetyltrimethylammonium chloride (CTAC) in concentrations above the cmc, where micelles are formed, all silver‐porphyrin complexes could be incorporated as monomers into the hydrophobic core of the micelles. In this way it was possible to investigate the kinetics of electron‐transfer of monomeric porphyrin complexes and to compare these with the behaviour in aqueous surfactant‐free solutions. Special attention was paid to measuring the activation barrier for an electron‐transfer from porphyrin complexes in the hydrophobic part of the micelles to redox ions in the surrounding solution. By varying the ionic strength of the solution and adding different types of surfactants, pure electrostatic effects could be separated from barriers which are created by an electron‐transfer through the surface of the micelles.—The mechanisms of these reactions are explained quantitatively to demonstrate the possibilities of

ISSN:0005-9021    

DOI:10.1002/bbpc.19810851011

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

年代:1981

数据来源: WILEY