Adhesion particle layer

Copper films for the polishing experiments were sputter deposited using a TORR International CRC-150 sputtering system on 6" blanket silicon wafers with tantalum as the adhesion promotion layer. The resistivity of the sputtered copper films was determined to be 2.5 jX2 cm. The slurries for the polishing experiment were prepared using a-alumina particles, with a bulk density of 3.7 g/cc, obtained from Ferro Corporation. The solids concentration was kept at 2 wt % unless otherwise stated. All the chemicals were purchased from Aldrich chemical company and were used without further purification. 

The mucociliary escalator functions when inhaled particles between 2 to 10 pm are deposited on the sticky mucous lining of the tracheobronchial tree and are propelled upward by the movement of this mucous layer in response to the beat of the cilia on the ciliated epithelial cells. This phenomenon is made possible because the mucous layer is biphasic, consisting of a watery solution in direct contact with the epithelia cells in which the cilia are free to beat. This watery solution is covered by a stickier, more adhesive gel layer that can trap and hold inhaled particles. The cilia beat in the wall layer at a rate between 1000 and 1500 strokes per minute such that at the point of their maximum upward velocity, the tips of the cilia come in contact with the gel layer to propel it upward. All recovery strokes subsequently occur in the water layer. This mechanism moves the mucus upward at a rate between 1 and 3 cm/minute. Ultimately, the mucus reaches the pharynx, where it is swallowed. Disease states that either alter the mucus-producing properties of cells in the tracheobronchial tree or decrease ciliary activity will obviously have a deleterious effect on this important clearance mechanism. 

In view of the fact that subsequently we will be considering the adhesion of a particle layer in air, the rheological properties of the adherent layer need not be taken into account. 

Packing pressure for particle layer, kgf/cm 10 Force of adhesion, kgf/cm ... 

With increasing wetting angle, the adhesion of the particle layer decreases i.e., a smaller number of particles will adhere to a hydrophobic surface than to a hydrophilic surface. 

The wetting angle can be used to estimate the adhesive tendencies of powders [196]. For the adhesion of the particle layer, a definite correlation has been found between wettability and adhesive force. 

The adhesion of a particle layer, as determined by the surface inclination technique in certain organic solvents, was found to be as follows [190] ... 

Under these conditions, the adhesive force of the particle layer is roughly proportional to the particle size. A similar relationship between adhesive force and the size of quartz particles was observed [190] in certain alcohols. 

Certain Features of Particle Adhesion to Plates. In examining the adhesion of a particle layer to plates, two important circumstances have been neglected [259]. First, the presence of particles previously adhering is often ignored, i.e., it is considered that each contact of the particle is with the original surface. Second, the dust deposition takes place not only on the facing (upper) side of the plate, but also on the lower (rear) side. Let us now examine the influence of these factors on the adhesion of particles from an air flow. 

As we have demonstrated, the adhesion-type detachment of a layer of adherent particles (denudation) depends on the air-flow velocity, while autohesion-type detachment (erosion) depends on the flow velocity and the time during which the air stream is acting on the dust, as expressed in terms of arbitrary quantities. In many studies, unfortunately, no distinctions have been made as to the specific features of removal of the adherent particle layer, the time of detachment has not been recorded (this is usually a long period, greater than 5 min), and the results of detachment are evaluated solely in terms of the air-flow velocity. The following data relate to the flow velocities at which removal of the layer of adherent particles has been observed ... 

The degree of removal of adherent particles was influenced by the time elasped since the particle layer was formed. As this period was increased to 168 h, the adhesion number increased from 16 to 48% in tests in which the layer was formed at 25°C. When the layer was formed at 80°C, there was no detachment of the adherent layer, i.e., the adhesion number was 100%. 

Fig. 5.83 The morphology of an adhesive layer on a Post-it (3M trademark) product is shown in these SEM micrographs. The surface of the adhesive coating appears to be composed of oblate spheroidal shaped particles (A). A thinner, particulate filled coating appears to cover the paper fibers between these adhesive particles. Two strips of adhesive were attached to one another and partially pulled apart, as shown in the insert (B). Strings of adhesive are seen to connect the two strips (B-D). (From D. R. Sawyer, unpublished [396].)...

In the opinion of the authors of [22], F is the force corresponding to the autohesion of individual particles in the layer,i.e., the specific strength of the powder layer. However, this assertion does not entirely agree with the facts. For F d > F we in fact have F = Faut > but if Fad < aut > we have F = Fad > 3.nd then the detachment of the particle layer is of the adhesive type. 

In order to secure a more accurate estimate of the adhesive force we must base our calculations on the number of contacts between the particles and the surface rather than the cross-sectional area of the particles [21]. Then the adhesion of a particle layer (F ) may be expressed by the equation... 

This comparison is only possible in connection with the adhesion-type detachment of the particle layer. 

Abrasives are hard, inert particles such as silicon carbide and aluminum oxide used for cutting, shaping, polishing, or cleaning. The adhesive functions as a binder in the manufacture of bonded and coated abrasives. A bonded abrasive such as a grinding wheel is a molded mixture of abrasive particles and binders. In a coated abrasive, e.g., sandpaper or emery paper, a particle layer is glued to a flexible backing. The predominant binder is phenolic resin (Table 30). 

Figure 34.9 (Upper) SEM of defects in thin supported -/-alumina layer the major defect in the top middle is caused by a surface defect in the support in the lower left is an adhesion defect the smaller defects are related to a less than optimum deposition viscosity. (Lower) FIB TEM of continuous film formed by deposition of 0p = 10 nm particles. Layer formation was promoted by the addition of polyvinyl alcohol (PVA) to the aqueous dispersion medium.

The adhesion between two solid particles has been treated. In addition to van der Waals forces, there can be an important electrostatic contribution due to charging of the particles on separation [76]. The adhesion of hematite particles to stainless steel in aqueous media increased with increasing ionic strength, contrary to intuition for like-charged surfaces, but explainable in terms of electrical double-layer theory [77,78]. Hematite particles appear to form physical bonds with glass surfaces and chemical bonds when adhering to gelatin [79]. 

Dispersion Processing. A commercial aqueous dispersion of Teflon PEA 335 contains more than 50 wt % PEA particles, about 5 wt % surfactants and fillers. This dispersion is processed by the same technique as for PTEE dispersion. It is used for coating various surfaces, including metal, glass, and glass fabrics. A thin layer of Teflon PEA coating can also serve as an adhesive layer for PTEE topcoat. 

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