Adhesion particle

When investigating time parameters it was shown, that a storage time in Xe of spectral purity was 10 mcs, while a restoring time was 10 ms with subsequent decrease in the case of addition of small amounts of air (less than 1%). As basic processes influencing time parameters, both dissociative recombination and three-particle adhesion of electrons to oxygen molecules have been considered. 

Interaction of Solids With Flotation Reagents. For flotation to occur with the aid of reagents, such compounds must adsorb at the sohd—hquid interface unless the soHd to be floated is naturally hydrophobic. In this latter case only depression can be attempted by the use of additional ions or depressants that hinder bubble—particle adhesion. Frothers (typically long-chain alcohols) and/or modifying agents such as hydrocarbon oils can, however, be used to enhance the collection of naturally hydrophobic soflds such as M0S2, talc, or plastics. 

While toner particles were used to exemplify a specific technology and lay the groundwork for discussing the scientific issues surrounding particle adhesion, the topic of particle adhesion extends far beyond copiers. For example, let us consider the fabrication of semiconducting devices. 

Another technological area that relies on particle adhesion is pharmacology. Consider, for example, an aerosol-dispensed medication. Here, the active ingredient relies on its adhering to inert carrier particles to be dispensed. However, it is crucial that the carrier particles do not adhere to the container walls, or much of the medication would never reach the patient. 

The manufacture of sintered parts such as gears and bushings and that of composite materials are, in a sense, also applications of particle adhesion. After all, a sintered part is simply a part manufactured from a powder that has been subjected to conditions that would encourage the particles to strongly cohere. Similarly, a composite material is one where particles of one or more materials are combined in some fashion so as to adhere within a matrix, thereby imparting certain properties to the composite that none of the materials possess in their own right. 

The results obtained in this way are the familiar results found by Hertz. More complete treatments of the contact mechanics of particle adhesion are given in Johnson [49] and in Timoshenko and Goodier [28]. 

This expression relates the action-at-a-distance forces between atoms to the macroscopic deformations and dominated adhesion theoiy for the next several decades. The advent of quantum mechanics allowed the interatomic interactions giving rise to particle adhesion to be understood in greater depth. 

By comparing Eqs. 17 and 20, it is clear that the Lifshitz s and Hamaker s treatments of particle adhesion are equivalent if... 

Johnson, Kendall and Roberts used an energy-based contact mechanics approach to understand particle adhesion. In their theory, they deviated from the earlier Derjaguin and Krupp models by assuming that tensile stresses are present... 

Whereas the JKR model approached the topic of particle adhesion from a contact mechanics viewpoint, the DMT theory simply assumes that the adhesion-induced contact has the same shape as a Hertzian indentor. The normal pressure distribution Ph(p) for the Hertzian indentor is related to the repulsive force and the distance from the center of the contact circle to the point represented by r according to the relationship [49]... 

Lest one be lulled into a false sense that, assuming that the JKR theory properly describes particle adhesion within its regime, DeMejo et al. [56] also reported that, for soda-lime glass particles with radii less than about 5 p.m, the contact radius varied, not as the predicted but, rather, as Similar results were reported for other systems including polystyrene spheres on polyurethane [58], as shown in Fig. 2, and for glass particles having radii between about 1 and 100 p,m on a highly compliant, plasticized polyurethane substrate [59] as illustrated in Fig. 3. 

Still another area where chemical and physical interactions can occur involves the enhancement of particle adhesion due to capillary condensation [69]. However, for the purposes of the present discussion, let us limit ourselves to dry particles. 

With these caveats, it is clear that, in general, particle adhesion is governed by physical, rather than chemical, interactions. Therefore, let us turn our attention to understanding the nature of the physical interactions that lead to the adhesion of particles to substrates. 

It is clear that the presence of electrostatic charges, whether due to contact charging, fractoemissions, or some other mechanism, will affect particle adhesion. However, to date there has been no satisfactory attempt made at properly integrating electrostatic forces into partiele adhesion theory. 

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