Force of adhesion

The intermolecular forces of adhesion and cohesion can be loosely classified into three categories (7) quantum mechanical forces, pure electrostatic... 

Adhksions falugkeit, /. adhesiveness. fett, n. adhesive grease, -kraft, /. adhesive power force of adhesion, maase, /. adhesive substance, adhesive. vermtigen, n. adhesive power. 

Non-epitaxial electrodeposition occurs when the substrate is a semiconductor. The metallic deposit cannot form strong bonds with the substrate lattice, and the stability conferred by co-ordination across the interface would be much less than that lost by straining the lattices. The case is the converse of the metal-metal interface the stable arrangement is that in which each lattice maintains its equilibrium spacing, and there is consequently no epitaxy. The bonding between the met lic lattice of the electrodeposit and the ionic or covalent lattice of the substrate arises only from secondary or van der Waals forces. The force of adhesion is not more than a tenth of that to a metal substrate, and may be much less. 

If, when a liquid drop is placed on a smooth surface, the forces of adhesion between the solid and the liquid are greater than the forces of cohesion of the liquid, then the liquid will spread and will perfectly wet the surface spontaneously. If the forces reach an intermediate balance determined by the interfacial energies ylv, ysj and ysv, then the liquid drop will form a definite contact angle (0) with the solid surface (Figure 4.12). 

From the above discussion it is apparent that while charge can cause particles to come together, it cannot be a significant factor in determining the force of adhesion with conductive particles. With perfect insulators, very high charge levels (corresponding to ps > 100 V/micron) can result in an effective force of adhesion. 

Ks Smolukowski flocculation coefficient, meters3/sec Kw Proportionality factor in equation for force of adhesion by van der Waal s forces, N/meter K6 Proportionality factor, C/meter2 Ksg Proportionality factor, V/meter In Natural logarithm of L Distance between centers of two particles or bodies, meters Lm Migration distance, meters Ls Clearance between proximate surfaces of two bodies, meters... 

Substituting Eq. (1.42) into Eq. (1.40) gives the force of adhesion at contact in terms of the surface energy ... 

If all or nearly all the hydroxyl groups are esterified (as in cellulose trinitrate), then the long-chain-molecules again possess a regular structure, and under the influence of forces of adhesion (van der Waals bonds) close mutual contact may be maintained (Fig. 89a). Here again the solvent may be too weak as to push aside... 

The intermolecular forces of adhesion and cohesion can be loosely classified into three categories quantum mechanical forces, pure electrostatic forces, and polarization forces. Quantum mechanical forces give rise both to covalent bonding and to the exchange interactions that balance tile attractive forces when matter is compressed to the point where outer electron orbits interpenetrate. Pure electrostatic interactions include Coulomb forces between charged ions, permanent dipoles, and quadrupoles. Polarization forces arise from the dipole moments induced in atoms and molecules by the electric fields of nearby charges and other permanent and induced dipoles. 

Capillary action, the rise of liquids up narrow tubes, occurs when there are favorable attractions between the molecules of the liquid and the tube s inner surface. These are forces of adhesion, forces that bind a substance to a surface, as distinct from the forces of cohesion, the forces that bind the molecules of a substance together to form a bulk material. By finding a relation between the height to which a liquid climbs in a tube of known diameter, we can use the height to determine the surface tension. 

Tokumura, F., Ohyama, K., Fujisawa, H., Suzuki, M., and Nukatsuka, H., Time-dependent changes in dermal peeling force of adhesive tapes. Skin Res. Technol. 5, 1999, 33-36. 

Attraction also occurs between the paper of the smelling blotter and the perfume materials. The attraction forces between the perfume and the solid support upon which it has been deposited are called forces of adhesion, and the degree of adhesion is often designated by the term substantivity. Adhesion plays a major role in the persistence of perfume on the skin, of the perfume from shampoos or conditioners on the hair, of detergent and fabric softener perfumes on textile fibers. 

In the absence of interparticle bonding material, the forces of adhesion are reasonably well understood and are orders of magnitude weaker than those discussed above. The results of many theoretical and experimental investigations of these long-range forces have been summarized by Krupp [6]. 

As explained under the adsorption theory of adhesion,3 an adhesive must first wet the substrate and come into intimate contact with it. (A brief description of the adsorption theory of adhesion is presented in the section below.) The result of good wetting is simply that there is greater contact area between adherend and adhesive over which the forces of adhesion (e.g., van der Waals type of forces) may act. For good wetting, the surface free energy (surface tension yLV) of the liquid adhesive must be less than that (critical surface tension yc) of the solid adherend, or... 

W.R. Bowen, N. Hilal, R.W. Lovitt and C.J. Wright, A new technique for membrane characterisation direct measurement of the force of adhesion of a single particle using an atomic force microscope, J. Membrane Sci. 139 (1998) 269-274. 

Other forces existing between particles often operate against hydrodynamic drag that produces fluidization. Thus, when particles touch one another, there exists a London-van der Waals force of a molecular nature at the point of contact. This force looms in proportion when gravity and drag forces diminish as a particle becomes smaller. For a small particle, the surface force of adhesion may often be thousands of times greater than its weight. 

Surfactant Molecule, , Displace Some Water Molecules from Surface Forces of Adhesion X. Low... 

The Area of Contact Increases When Lower Forces of Adhesion Replace the High Forces of Cohesion... 

Figure 2.7 Effect of surfactant on surface tension, (a) Because of high forces of cohesion, there is little contact between droplet and surface in the absence of surfactants, (b) The area of contact increases when lower forces of adhesion replace the high forces of cohesion. (From Hassall, K.A., The Biochemistry and Uses of Pesticides, 2nd ed., VCH Publishers, New York, 1990. With permission.)...

An adhesive is a material capable of holding together solid materials by means of surface attachment. Adhesion is the physical attraction of the surface of one material for the surface of another. An adherend is the solid material to which the adhesive adheres and the adhesive bond or adhesive joint is the assembly made by joining adlierends together by means of an adhesive. Practical adhesion is the physical strength of an adhesive bond It primarily depends on the forces of adhesion, but its magnitude is determined by the physical properties of the adhesive and the adherend, as well as the engineering of the adhesive bond. 

In our treatment of particle removal we shall make a number of simplifying assumptions. We shall assume that the force of adhesion is only due to Van der Waals force of attraction. We shall not consider other possible forces such as electrostatic interactions or gravity. We shall also assume that the surface is smooth. In other words, the roughness of the surface is due to randomness at the atomic level. This means that over the width of the particle, the surface height varies by a few angstroms at most. This assumption allows us to readily determine the force of adhesion of glass particles... 

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