Aggregates Rupture

Foams Two excellent reviews (Shedlovsky, op. cit. Lemlich, op. cit.) covering the literature pertinent to foams have been published. A foam is formed when bubbles rise to the surface of a liquid and persist for a while without coalescence with one another or without rupture into the vapor space. The formation of foam, then, consists simply of the formation, rise, and aggregation of bubbles in a hquid in which foam can exist. The hfe of foams varies over many magnitudes—from seconds to years—but in general is finite. Maintenance of a foam, therefore, is a dynamic phenomenon. 

The general form of the population balance including aggregation and rupture terms was solved numerically to model the experimental particle size distributions. While excellent agreement was obtained using semi-empirical two-particle aggregation and disruption models (see Figure 6.15), PSD predictions of theoretical models based on laminar and turbulent flow considerations... 

O The cause of an acute coronary syndrome is the rupture of an atherosclerotic plaque with subsequent platelet adherence, activation, and aggregation, and the activation of the clotting cascade. Ultimately, a clot forms composed of fibrin and platelets. 

Rupture of fractal (flocculated) aggregates of polystyrene latices in simple shear flow and converging flow was studied by Sonntag and Russel (1986, 1987b). For simple shear flow and low electrolyte concentrations, the critical fragmentation number decreases sharply with agglomerate radius (R) as... 

Most recently, Horwatt, Manas-Zloczower, and Feke (1992a, b) carried out a numerical study of the rupture of fractal clusters generated by different aggregation protocols (more details of these protocols are given in Section... 

On repeated freeze-drying of microgels with EUP-components an irreversible formation of an insoluble aggregate was observed [ 135]. It was supposed that this aggregation is due to radical reactions between adjacent microgel particles. The radicals are possibly formed by a mechanical rupture of chains due to stresses within the particles caused by freezing. 

In carotid atherosclerosis, plaques may rupture, resulting in collagen exposure, platelet aggregation, and thrombus formation. The clot may cause local occlusion or may dislodge and travel distally, eventually occluding a cerebral vessel. 

Changes in density, unit cell dimensions, and macroscopic volume have serious effects. In an environment where point defects (or aggregates of point defects) are generated, such as in the components of nuclear reactors, or in vessels used for the storage of nuclear waste, where point defects are produced as a result of irradiation, dimensional changes can cause components to seize or rupture. 

A number of factors increase the risk of disruption of the plaque the presence of a considerable amount of fat in the plaque the effects of physical stress on the vessel wall, particularly in the hypertensive patient and the activity of macrophages. Macrophages release proteases (e.g. colla-genase, elastase) which lead to breakdown of the plaque. Rupture of the plaque produces fissures that are sites for aggregation of platelets. Fragments from the rupture can occlude blood vessels. 

Mention should be made in this connection of the physics and chemistry involved in faulting as well as in jointing and minor movements of the solid rocks. These phenomena have often been treated under the principles of elastic theory as applied to homogeneous bodies, yet there can be no question that the elastic properties and conditions of rupture of aggregates must differ in many essential particulars from those of homogeneous bodies. Here is a considerable field for experimentation. 

A model has been developed to describe the penetration of polydimethylsi-loxane (PDMS) into silica agglomerates [120]. The kinetics of this process depend on agglomerate size and porosity, together with fluid viscosity. Shearing experiments demonstrated that rupture and erosion break-up mechanisms occurred, and that agglomerates which were penetrated by polymer were less readily dispersed than dry clusters. This was attributed to the formation of a network between sihca aggregates and penetrated PDMS, which could deform prior to rupture, thereby inhibiting dispersion. 

Munkholm, L.J. and Kay, B.D. 2002. Effect of water regime on aggregate tensile strength, rupture energy and friability. Soil Science Society of America Journal 66 702-709. 

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