Properties of the adsorption layer

According to the concepts, given in the paper [7], a significant difference between the values of yield stress of equiconcentrated dispersions of mono- and polydisperse polymers and the effect of molecular weight of monodisperse polymers on the value of yield stress is connected with the specific adsorption on the surface of filler particles of shorter molecules, so that for polydisperse polymers (irrespective of their average molecular weight) this is the layer of the same molecules. At the same time, upon a transition to a number of monodisperse polymers, properties of the adsorption layer become different. 

Indeed, a direct relationship between the lifetimes of films and foams and the mechanical properties of the adsorption layers has been proven to exist [e.g. 13,39,61-63], A decrease in stability with the increase in surface viscosity and layer strength has been reported in some earlier works. The structural-mechanical factor in the various systems, for instance, in multilayer stratified films, protein systems, liquid crystals, could act in either directions it might stabilise or destabilise them. Hence, quantitative data about the effect of this factor on the kinetics of thinning, ability (or inability) to form equilibrium films, especially black films, response to the external local disturbances, etc. could be derived only when it is considered along with the other stabilising (kinetic and thermodynamic) factors. Similar quantitative relations have not been established yet. Evidence on this influence can be found in [e.g. 2,13,39,44,63-65]. 

Certain antifoams, for example, methyl or ethyl alcohols, when introduced in the foaming solution, affect indirectly the foam stabilising properties of the adsorption layers because they change either the surfactant solubility or its CMC. It has been established [39] that addition of antifoams (2-ethylhexanoI and tributyl phosphate) increases CMC. Schick and Fowkes [40] have observed a certain change in CMC of NaDoS when tetradecanol is added. If the compounds added improve the foaming ability (such as dodecylglycol ether and (3-hydroxyethyl laurylamide), CMC decreases. 

It has been established [55] that hydrocarbon (decane, benzene) promoted foam breakdown, occurring with formation of unstable films (barrierless rupture), is only possible at very low surfactant concentrations (less than 0.003-0.004% saponin and OP-10). At higher surfactant concentrations the defoaming ability of the antifoam results from the lowering of the energy barrier of film rupture. The latter is determined by the properties of the adsorption layers and other film parameters. 

II.2. Structure and Properties of the Adsorption Layers at the Air-Water Interface... 

Therefore, the absolute value of the da /dc derivative equals the surface activity, G, not only in the limit of zero concentration (c- 0), but also within some definite concentration range, in which the properties of the adsorption layers can be described by eq. (II. 10). 

The solubility of lauric (Cl2) acid is sufficiently high, so that one is able to carry out the surface tension measurements. Yet at the same time, its solubility and dissolution rate are low enough for one to be able to study the properties of the adsorption layers formed with the Langmuir balance, provided that one works fast. The latter feature allowed Frumkin to compare trends in the 7rsM(7r) curves obtained for the same substance using methods established for both soluble and insoluble surfactants. The experimental... 

Good agreement between these two series of curves can serve as convincing evidence of the fact that the properties of the adsorption layers of both soluble and insoluble surfactants are close, and are not directly related to the solubility of surfactant molecules in the supporting liquid. 

Investigation of the mechanical properties of the adsorption layers formed with surfactant molecules of different nature has shown that the condensed adsorption layers can indeed be present in both solid and liquid states. Solid adsorption layers (Fig. 11-29, line 1) do not reveal irreversible... 

From these approximations one can conclude that in time intervals up to the order O(lOO tgj) the adsorption kinetics are controlled by the corresponding surfactant, for sodium dodecylsulfate up to some seconds. At longer times, the effect of surface active contaminants have to be taken into consideration. At times t 100 tgj, the properties of the adsorption layer can already be dominated by impurities. 

The coalescence rate, i.e. formation of larger droplets after collision of two droplets, depends on the number of collisions and on the properties of the adsorption layers. For dilute emulsions, as well as emulsions having V2 = 0.3—0.74, coalescence is the main process leading to the disturbance of their aggregative stability. Hence, prerequisite for the production of appreciable volumes of any type of emulsions suitable for practical application is provision of their coalescence stability. In case of o/w emulsions, maximum stability against coalescence is achieved through the formation, on the surface of the disperse phase particles, of structured adsorption layers, a structure-mechanical barrier defined by Rehbinder [8]. Such layers are... 

The Boussinesq-Scriven constitutive law postulates that = rj id. The surface viscosity, however, being a property of the adsorption layer itself, should be related to the relative displacement of the adsorbed molecules. As a result the dilatational surface viscous stress should be proportional to the rate of local deformation, i.e.. For insoluble... 

Although the known methods of chemical treatment of capillary walls are readily realizable, they have a serious disadvantage, namely, they are not universal and are restricted as a rule to glass and metal columns. Moreover, the composition and properties of the adsorption layer formed strongly depend on the composition of the column material, which may vary widely. 

Investigation of the rheological properties of the adsorption layers and bilayer emulsion films was performed under... 

IV. PROPERTIES OF THE ADSORPTION LAYER AND STABILITY OF AEROSIL DISPERSIONS IN BINARY LIQUIDS... 

Figure 9 Characterization of the equilibrium properties of the adsorption layer by ellipsometry and Surface second harmonic generation, SHG. The SHG-signal I (P = 45, d = 90) (circles) is proportional to the surface coverage and increases monotonously with the bulk concentration. The ellipsometric quantity dA = A - Ao (triangles) shows an extremum at an intermediate concentration far below the cmc. The inset clearly shows the nonmonotonic dependency of dA on the adsorbed amount, (redrawn from (20 )...

It is connected with the situation when one suggests that the properties of the system, contained many macromolecules and surface, equal to the properties of the macromolecule in adsorption layer. It is not true in some cases. For example, for the polymer adsorption from concentrated solutions, the polymer link density in the adsorption layer is not equal to the density of links of one of the macromolecules in it. In some cases, the properties of the adsorption layer depend on the way it forms, but not only on the properties of macromolecules in it. We suggest that the following can be taken into account when the theory is based on the following features ... 

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