摘要:

The foam stabilizing ability of anionic, cationic and nonionic surfactants are studied with two methods, involving constant and variable capillary pressure in the foam liquid phase: the method of determining the foam lifetime at constant pressure and the Ross-Miles test. It is reported that the most important parameters for foam stability are the capillary pressure and the type of the foam films. It is proved that the foam lifetime τpdetermined at constant capillary pressure is a more precise and defined characteristics of foam stability.

ISSN:0193-2691    

DOI:10.1080/01932699708943759

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper presents a review of our recent studies on the lateral capillary forces and on their role in the formation of two-dimensional ordered arrays of colloidal particles or protein molecules. To reveal the mechanism of protein ordering in liquid films we carried out model experiments with micrometer sized latex particles. The films were formed on solid or liquid substrates. By variation of the electrolyte concentration, the particle charge and volume fraction we proved that neither the double layer repulsion, nor the van der Waals attraction between the particles, was responsible for the formation of the two-dimensional arrays. Direct microscope observations revealed that the process of ordering was triggered by attractive lateral capillary forces due to the overlap of the menisci formed around the particles. Two types of lateral capillary forces, flotation and immersion, could be distinguished and theory of these interactions was developed. The lateral capillary forces between a floating particle and a wall were also studied; they could be employed for precise determination of the shear surface viscosity.

ISSN:0193-2691    

DOI:10.1080/01932699708943760

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A theoretical approach to the diffusion controlled kinetics of adsorption on the expanding interface of surfactant solutions is developed and compared with the experiment. This approach being an analogue of von Karman's approach to the hydrodynamic boundary layer is applicable to both submicellar and micellar surfactant solutions under large deviations from equilibrium. The partial differential equations of the convective diffusion are reduced to a set of ordinary differential equations of first order and algebraic equations. This simplifies the numerical computations and enhances the interpretation of the experimental data. Dynamic surface tension data for solutions of sodium dodecyl sulfate obtained by the maximum bubble pressure method are interpreted. Reasonable results for the diffusivity of monomers and the rate constant of micellar disintegration have been obtained.

ISSN:0193-2691    

DOI:10.1080/01932699708943761

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

First we review some recent studies devoted to the role of surface moments (torques) in the mechanics and thermodynamics of fluid interfaces of arbitrary shape. The presence of bending and torsion moments leads to a difference between the mechanical and thermodynamical surface tensions and shear stresses. Next we review recent results in the mechanics of thin liquid films and the transition region film-Plateau border. Line and transversal tensions are assigned as excesses on the contact line. The transversal tension accounts for the attractive forces in the transition zone. Experiments with floating bubbles show that the movement of the contact line can lead to non-equilibrium values of the line tension, which can be interpreted in terms of a plastic deformation.

ISSN:0193-2691    

DOI:10.1080/01932699708943762

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present theoretical treatment and experimental data on the factors of stabilisation within emulsion systems. First a brief description of the hydrodynamic theory of thinning of emulsion films in the presence of surfactants is provided. This theory could be applied to explain the empirical Bancroft rule and some effects related to the HLB scale of surfactants. Complimentary experimental methods for investigating of model emulsions - films, drops and batch systems are described. An overview of our experimental data on the behavior of emulsions stabilised with non-ionic surfactants and proteins is provided. Attention is then turned to two recently uncovered phenomena of stabilisation of emulsion films, arising from surfactant re-distribution between the phases.

ISSN:0193-2691    

DOI:10.1080/01932699708943763

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Some aspects of DLVO and non-DLVO forces in colloidal systems are over-viewed. The influence of long range interactions on some kinetic properties of dispersions, as Brownian diffusion, is discussed. It is shown, both theoretically and experimentally, that the electrostatic repulsion increases the collective diffusivity. The film stratification and oscillatory structure forces in colloidal suspensions are considered within the framework of an uniform approach The presence of small colloidal species (e. g. micelles or polymer molecules) may lead to several maxima and minima in the disjoining pressure isotherm. The particular case of interacting emulsion droplets is examined accounting for the interfacial deformability. The droplet deformation acts as a soft repulsion but affects also the remaining contributions to the interaction energy due to changes of the droplet shape. A general procedure for calculating the inter-droplet interaction energy, as well as the equilibrium film radius and thickness in a doublet of droplets, is suggested. The energy of interaction between charged colloidal particles, due to correlations of the density fluctuations in the electric double layer is also studied. It is found that this effect may lead to attraction greater than the van der Waals contribution, especially when multivale counter ions are present.

ISSN:0193-2691    

DOI:10.1080/01932699708943764

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The influence of pH on the properties of polyacryloylacetone (PAA) monolayers at air/water interface was examined by using surface pressure-area isotherm measurement,a new rheological approach and AFM imaging. The isotherms and AFM-imaging detect phase transitions in PAA monolayers and growth of microdomains during compression in the case of pH 6.6 and missing of such kind of structures at pH 9. The rheological study below and above the phase transition shows an existence of a large relaxation time related to the process of formation of microdomains.

ISSN:0193-2691    

DOI:10.1080/01932699708943765

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new approach is proposed for the study of short-range molecular interactions between first neighboring molecules in amphiphile bilayers by means of experimentally determined dependencies of the bilayer mean lifetime on the surfactant concentration and of the critical concentration for bilayer formation on the temperature. Short-range molecular interactions are demonstrated by the parameters binding energy Q of an amphiphile molecule in the bilayer and specific line energy γ of the nucleus hole. These parameters are calculated from the experimental dependencies by using the hole-nucleation theory [D. Kashchiev and D. Exerowa, J. Colloid Interface Sci., 77, 501 (1980)] describing the stability of amphiphile bilayers. It is shown the decisive role of the short-range molecular interactions for the bilayer stability and the occurrence of first-order phase transition in phospholipid foam bilayers. The values of Q and γ are calculated for various amphiphile bilayers: anionic and nonionic surfactants, phospholipids and their natural mixtures.

ISSN:0193-2691    

DOI:10.1080/01932699708943766

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Cross-How filtration of bentonite-in-water suspensions is studied experimentally in a small laboratory device. The Theological behaviour and the filtration resistance in batch filtration are independently established. Both transient and steady-state data indicate channel constriction by a dense cake layer. Quantitative estimates based on measured parameters show that steady-state conditions can be ensured by tangential flow of the dense pseudoplastic bentonite cake. Steady-state is possible when the shear stress at the moving boundary feed suspension/dense cake exceeds appr.l Pa (at lower values of the shear stress the cross-flow microfiltration channel gets plugged). The material characteristics of the dense cake, which determine cross-flow filtration behaviour, are the viscosity and the specific filtration resistance. Indirect estimates of these quantities from measured cross-flow filtration parameters are consistent with results from direct measurements. The data support the convective model of cross-flow microfiltration.

ISSN:0193-2691    

DOI:10.1080/01932699708943767

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The influence of different surfactants on the possibility to obtain fine dispersions with a comparatively high percentage of cellulose acethophthalate (CAP) has been investigated. A method for obtaining concentrated dispersions of CAP including the anti-glaucoma drug pilocarpine hydrochloride has been proposed.

ISSN:0193-2691    

DOI:10.1080/01932699708943768

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor