Adhesion of particles

Bouncing may be regarded as a defect in the particle-deposition process. However, particles that have been deposited in filters may subsequently be blown off and reentrained into the air stream (Corn, Adhesion of Particles, in Davies, Aerosol Science, Academic, New York, 1966 and Davies, op. cit.). 

Let us now turn our attention to understanding the nature of the interactions giving rise to the adhesion of particles to surfaces. First, one should recognize that most particles commonly encountered have been exposed to ambient conditions for lengthy times. As a result, any functionally reactive groups on the 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. 

As previously mentioned, electrodynamic interactions, such as those arising from London forces, can also contribute to the adhesion of particles. These forces are dominated by dipole interactions and are broadly lumped into the classification known as van der Waals interactions. A more detailed description of van der Waals interactions than can be presented in this article is given in books by Israelachvili [95] and by Rimai and Quesnel [96]. 

All things considered, the study of the adhesion of particles will likely remain a vibrant field for years to come, offering challenges and opportunities to those who seek them in this field. 

Adhesion of particles Small particles experience adhesion forces, allowing them to attach to surfaces. These forces may be made up from surface tension of liquid films, or London (Van der Waals) forces. 

The removal rate of particles or the rate of flotation from pulp is essentially governed by (i) collision between particles and bubbles (ii) adhesion of particles to bubbles and (iii) detachment of particles from bubbles. Keeping these factors in mind, one can arrive at the following relationship ... 

One consequence of the curvature dependence of the vapor pressure is capillary condensation, that is the spontaneous condensation of liquids into pores and capillaries. Capillary condensation plays an important role for the adsorption of liquids into porous materials and powders. It also causes the adhesion of particles. The condensing liquid forms a meniscus around the contact area of two particles which causes the meniscus force. ... 

So far we have assumed that the interacting surfaces are not deformable. In reality all solids have a finite elasticity. They deform upon contact. This has important consequences for the aggregation behaviour and the adhesion of particles because the contact area is larger than one would expect from infinitely hard particles. 

Successful assembly requires matching features of the template, meaning that wavelength and height have to be of the same dimensions. Additionally, adhesion of particles and surface must be avoided by weak repulsive forces. In this context, polyelectrolyte multilayer-wrinkles are particularly useful, as the wettability of the multilayer is determined by the part of the layer adjacent to the film/solution or film/air interface respectively, while the elastic properties are determined by the total film [84], Thus, elastic constants can be adjusted largely independent from wettability properties. 

Esmen, N.A., Ziegler, P. Whitfield, R. (1978) The adhesion of particles upon impaction. Journal of Aerosol Science, 9, 547-66. 

Electric double-layer forces result from the contact between two compounds of different contact potential. In a dry environment, electric double-layer forces are only significant for particles less than 5 pm in diameter [267]. Lewis acid-base interactions, determined by the chemical composition of the surface, may be used to alter the adhesion of particles. However, if capillary... 

In rotational molding, two bulk movements dominate the melt deposition and densification 1) the adhesion of particles on the mold surface and 2) the melting and collapse of the particulate structure. The latter... 

It may seem as if the two mechanisms exclude each other. However, since Pvdw decreases with /a and P remains almost constant, even over macroscopic distances, the electrical double layer will contribute to the adhesion of particles, particularly if the contact surfaces are rough. 

Figure 22 A (not to scale) reminder that interaction forces leading to adhesion of particles to biological surfaces compete with particle flow, medium flow, and shear forces but, most importantly, it should be noted that attractive forces come into play at very small distances, that is, <10 nm. For those particles which adhere, there are shear forces which act to detach the nanoparticles, and there is the potential for particles to roll if they are spherical.

Therefore, using moisture sorption, microcalorimetric, IGC, molecular modelling and other techniques, the consequences of the particle size reduction process can be assessed. Moreover, surface energetics can be measured directly and predictions made about the nature of the surface, which ultimately could affect properties such as the flow of powders or adhesion of particles (Podczeck et al. 1996b). 

They affect contact angles and thereby capillary phenomena such as wetting, adhesion of particles, capillary displacement, and dispersion of powders in a liquid. 

When the zeta-potential equals zero, fast flocculation stage prevails and the probability of collision-adhesion of particles increases. In addition, the effect of electrolytes is also small. 

On such defective surfaces the adhesion of particles is improved as compared with freshly cleaved graphite, but force interactions between tip and sample are still evident in the measurements. An example for a model electrode, which was prepared by electrophoretic deposition of a platinum colloid onto a defective HOPG surface, is shown in Fig. 4. 

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