Capillary and adsorptive force

Combination of Capillary and Adsorptive Forces Affecting Underground Liquid Movement... 

The physical mechanisms underlying the effect of moisture on interparticle cohesion have received considerable attention in the soil physics literature and now are well understood. The total potential energy of soil water arises from both capillary and adsorptive forces and is represented as the matric potential (rlfm)- The relation of (Pa) to the humidity of the air within the soil voids is modeled by the Kelvin equation ... 

Both adsorptive and capillary forces play an important part in soil-liquid interaction (see Figure 18.3). This is very important for unsaturated soil. The total force (i.e., the sum of capillary force and adsorptive force) is termed the matrix potential, which has a negative gage pressure relative to the external gas pressure on the soil water (more often the gage pressure is referred to as the atmospheric pressure). 

Wanless E J and Christenson H K 1994 Interaction between surfaces in ethanol adsorption, capillary condensation, and solvation forces J. Chem. Rhys. 101 4260-7... 

Fig. 3.10 Contributions to the lowering of chemical potential of the condensed liquid in a capillary, arising from adsorption forces (c) and meniscus curvature (Ap). The chemical potential of the free liquid is , and that of the capillary condensed liquid is (= ) z is the distance from the capillary wall. (After Everett. )...

Granulation by pelletizing involves preliminary formation of agglomerates from uniformly moistened particles or deposition of dry particles on moistened substance in the granulation centers. Such a process is attributable to th action of capillary adsorptive forces between particles and to subsequent compaction of the structure due to forces of interaction between the particles within the compact dynamic layer. 

The dyeing procedure for paper can be described basically by two processes the penetration of the dye molecule into the capillary spaces of the cellulose and then its adsorption on the surface of the fiber. The bonding forces are due to the effects charge (ionic bonds), precipitation, and intermolecular forces. 

There is no simple, direct relationship between elasticity and emulsion or foam stability because additional factors, such as film thickness and adsorption behaviour, are also important [204]. Nevertheless, several researchers have found useful correlations between EM and emulsion or foam stability [131,201,203], The existence of surface elasticity explains why some substances that lower surface tension do not stabilize foams [25]. That is, they do not have the required rate of approach to equilibrium after a surface expansion or contraction as they do not have the necessary surface elasticity. Although greater surface elasticity tends to produce more stable bubbles, if the restoring force contributed by surface elasticity is not of sufficient magnitude, then persistent foams may not be formed due to the overwhelming effects of the gravitational and capillary forces. More stable foams may require additional stabilizing mechanisms. 

In the last decade, a variety of microporous and mesoporous materials have been developed for applications in catalysis, chromatography and adsorption. Great attention has been paid to the control of (i) pore surface chemistry and (ii) textural properties such as pore size distribution, pore size and shape. Recently, a new field of applications for these materials has been highlighted [1-3] by forcing a non-wetting liquid to invade a porous solid by means of an external pressure, mechanical energy can be converted to interfacial energy. The capillary pressure, Pc p, required for pore intrusion can be written from the Laplace-Washbum relation,... 

A variant is the micro-pipette method, which is also similar to the maximum bubble pressure technique. A drop of the liquid to be studied is drawn by suction into the tip of a micropipette. The inner diameter of the pipette must be smaller than the radius of the drop the minimum suction pressure needed to force the droplet into the capillary can be related to the surface tension of the liquid, using the Young-Laplace equation [1.1.212). This technique can also be used to obtain interfacial tensions, say of individual emulsion droplets. Experimental problems include accounting for the extent of wetting of the inner lumen of the capillary, rate problems because of the time-dependence of surfactant (if any) adsorption on the capillary and, for narrow capillaries accounting for the work needed to bend the interface. Indeed, this method has also been used to measure bending moduli (sec. 1.15). 

Water forms a concave meniscus around the perimeter of a capillary tube due to the adsorption forces between the tube surface and the liquid as well as the cohesive forces finm the liquid surface, known as surface tension . The adhesion between the water molecules and glass surface tends to make the water move upward along the capillary sides and surface of water in the capillary concaves. Surface tension, on the contrary tends to level the surface in order to decrease the surface area. Simultaneous and repeated operation of these two phenomena results in capillary rise of water to a maximum height at which weight of water column equals upward component (cosine component) of surface tension force. The surface tension force acts all along the circumference (2nr) and tangential to the surface and is inclined at an angle 0 (Fig. 2.6). 

Common conceptual models for liquid distribution and transport in variably saturated porous media often rely on oversimplified representation of media pore space geometry as a bundle of cylindrical capillaries, and on incomplete thermodynamic account of pore scale processes. For example, liquid adsorption due to surface forces and flow in thin films are often ignored. In this study we provide a review of recent progress in modeling liquid retention and interfacial configurations in variably saturated porous media and application of pore scale hydrodynamic considerations for prediction of hydraulic conductivity of unsaturated porous media. 

When the mobile phase washes over the sample spot and starts on down the paper, it will begin to siphon when its level gets below the solvent level in the solvent tank. This will cause the solvent to move too fast for the desired separation equilibrium to be attained, and streaking will occur. If a small-diameter rod is placed so the entire width of the paper makes contact with it, then a considerable adsorption force is developed between the solvent and the rod. This is sufficient to stop the siphoning action, and the solvent moves down the paper by capillary action alone. 

Various theories have been offered to explain such changes in the heat of adsorption.1,2 One view is that a monolayer is first formed in which the molecules are held by stronger forces than in subsequent layers. Other workers ascribe variations to the heterogeneous nature of the surface. The molecules adsorbed initially may enter capillaries and crevices being held on several sides they should liberate more heat. Another suggestion is that the earlier portions are adsorbed by the more active surface atoms and are held by forces of a different nature than later portions. The last... 

The dominant effects of particular forces give rise to different energy categories of soil water. Thus, there are three main groups adsorption, capillary and gravitational waters. 

Particles consist of both internal and external surface area. The external surface area represents that caused by exterior topography, whereas the internal surface area measures that caused by microcracks, capillaries, and closed voids inside the particles. Since the chosen surface area technique should relate to the ultimate use of the data, not all techniques are useful for fine powders. The commonly used approaches are permeametry and gas adsorption according to the Brunauer, Emmet, and Teller (BET) equation [9]. Because of simplicity of operation and speed of operation, permeametry methods have received much attention. The permeametry apparatus consists of a chamber for placing the material to be measured and a device to force fluid to flow through the powder bed. The pressure drop and rate of flow across the powder bed are measured and related to an average particle size and surface area. Especially for porous powders, permeametry data include some internal surface area, thus decreasing their value. 

In the absence of complicating factors such as capillary condensation and competitive adsorption, the process of physical adsorption has no activation energy that is, it is diffusion-controlled and occurs essentially as rapidly as vapor molecules can arrive at the surface. The process will be reversible and equilibrium will be attained rapidly. Because the forces involved are the same as those involved in condensation, physical adsorption will generally be a multilayer process—that is, the amount of vapor that can be adsorbed onto a surface will not be limited simply by the available solid surface area, but molecules can stack up to a thickness of several molecules in a pseudoliquid assembly (Fig. 9.3). If the vapor pressure of the gas reaches saturation level, in fact, the condensation and adsorption processes overlap and become indistinguishable. The fact that physical adsorption can be a multilayer process is very important to the mathematical modeling and analysis of the process, as will be seen below. 

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