Adhesion interaction liquid-solid

Rubber swelling modifies the liquid/solid work of adhesion. Wo, because in addition to the initial liquid/solid interactions, liquid diffusion into the solid produces supplementary liquid/liquid interactions, hquid molecules having passed through the liquid/solid interface. Therefore, to the initial work of adhesion in the absence of swelling, Wq, an additional term corresponding to a fraction of the cohesion energy of the liquid, 2y, should be added. If / is the time of diffusion, the work of adhesion at /, Wo(t), can then be expressed as... 

It is informative to apply Equation (60) to low-energy surfaces for two extreme values of 0, 0° and 180°, for which cos 0 is 1 and — 1, respectively. For 0 = 0°, WSL = 2yLV = WAA the work of solid-liquid adhesion is identical to the work of cohesion for the liquid. In this case interactions between solid and solid, liquid and liquid, and solid and liquid molecules are all equivalent. At the other extreme, with 0 = 180°, WSI = 0. In this case the liquid is tangent to the solid there is no interaction between the phases. 

Knowledge of the surface dynamics of a solid has recently allowed significant progress in many academic and scientific fields adsorption (gas-solid interaction), wettability (liquid-solid), adhesion (solid-solid), and in applications catalysis [1,2], membrane [3,4], friction [5-8], blending [9,10],... 

Wu is the work of adhesion per unit area, y is determined by the intermolec-ular force between liquid molecules, y v is mainly caused by forces between solid molecules. The work of adhesion comes from the interaction between solid and liquid molecules. Hence the task of finding a relation Wa = Wa(j/. . ysv) is somehow similar to that of determining the force between a liquid and a solid molecule from knowledge of the force between two solid and two liquid molecules. In a strict sense this is impossible, and one can only hope for empirically verified and theoretically sound approximations. 

The work of adhesion is a direct measure of the free energy of interaction between solid and liquid,... 

However, other solid materials can also be used as capillary tubes when required.) It has been observed experimentally that there is an inverse proportionality between the height of the liquid present in the capillary tube and the radius of the tube (see also Section 6.1). Capillary rise was found to result from the adhesion interactions between the liquid and the capillary wall, which are stronger than the cohesion interactions within the liquid. This is a method used to measure the surface tension of pure liquids. During the measurement, the capillary tube must be very clean, placed completely vertical and be circular in cross section with accurately known and uniform radius. 

The work of adhesion (see Chapter 1,1) reflects the degree to which unsaturated molecular interactions between solids and liquids in contact are balanced. The value of cos 9, which is symbatic to the work of adhesion, is also a measure of the degree of similarity between the solid surface and a liquid (liophilicity). Polar surfaces that are wetted by water well are hydrophilic, while those poorly wetted (solid hydrocarbons, and particularly fluororinated polymers) are hydrophobic. Since the value of 0 is determined by both the work of adhesion and the work of cohesion, a comparison of the contact angles formed by different liquids at the same solid surface does not allow one to compare the works of adhesion (the degree of similarity in the nature of the liquid and solid) directly. For example, polar surfaces are equally wetted well by both water and hydrocarbons. 

It is also convenient to combine studies of polymer interactions with solid substrates with studies of the adsorption characteristics of the organic components themselves. Such an approach has much to offer in adhesion research and the basis of studies of adsorption from a liquid phase and its applicability in adhesion has been discussed in detail elsewhere [7] so it will not be treated in depth here. A brief overview will, however, provide a background to this approach. The determination of gas-phase adsorption isotherms is a well-known methodology in surface chemistry in this manner it is possible to describe adsorption as following Langmuir or other characteristic adsorption types. The conventional method of studying the adsorption of molecules from the liquid phase is to establish the depletion of the adsorbate molecule from the liquid phase. However, as first pointed out by Castle and Bailey [8], with the advent of surface analysis methods it is now... 

Control of adhesion interaction by the addition to adhesives of surface-active substances (surfactants) is of great theoretical and practical interest. The particular effects of siu-factants lie in their ability to decrease the surface tension of the solution due to positive adsorption on the surface. Coating the surface of solid bodies and of liquids with the finest layer of a surfactant added to the system in very small quantities permits changes of the conditions of phase interaction and the progress of the physical-chemical processes. 

Vignes-Alder, M. and Brenner, H., A micromechanical derivation of the differential equations of interfacial statics. III. line tension, 7. Colloid Interface Sci., 103,11,1985. Vogler, E.A., Practical use of concentration-dependent contact angles as a measure of solid-liquid adsorption. 1. Theoretical aspects, Langmuir, 8, 2005, 1992. Vrbanac, M.D. and Berg, J.C., The use of wetting measurements in the assessment of acid-base interactions at solid-liquid interfaces, J. Adhesion Sci. TechnoL, 4, 255, 1990. 

The work of adhesion at a solid-liquid interphase can be attributed to two interaction terms /16-19/ ... 

The interaction between solid and liquid due to polar groups has been considered by Fowkes [48] to be defined by acid-base interactions. In this model, Fowkes assumes that the interaction between two materials can be described by a component due to dispersion interactions in the form of a geometric mean relationship plus a component due to acid-base interaction. The acid-base interaction indicates the ability of a polar group on one surface to donate or accept electrons from polar groups on the other surface. The work of adhesion is then described by Eq. (5). 

Molecular interaction between particles and a surface depends on the thickness of the liquid layer between the contiguous bodies. Calculations show [163] that in aqueous electrolyte solutions, the molecular interaction between solids is completely screened at a distance of 10" cm between the solid bodies. At a distance of 10 cm, the molecular force is approximately half of its maximum value. For smaller distances, the molecular component of adhesion becomes greater, approaching the maximum value. 

Adhesion under the Influence of an Electric Field. Under the influence of an electric field in a liquid medium, the following processes may take place adhesion of particles to the surface, detachment of previously attached particles, and the formation of particle aggregates. The adhesive interaction is determined by the properties of the liquid medium and the particles and also by the strength of the electric field. The presence of solid particles in the liquid will change its conductivity. The surface conductance of a suspension can be expressed by means of a relative value Ar [203], the ratio between the conductance of the electrolyte and the conductance of a suspension of material in this same electrolyte. 

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