Aggregation flocculation

Lyophobic colloids (sols) may be prepared by grinding crystalline materials or running an electric arc between metallic electrodes, both in the dispersing medium. More commonly, they are prepared by precipitating the solid from a strongly supersaturated solution, which produces a large number of precipitation nuclei. Because there is little attractive interaction between the particles and the medium, attractive forces between the particles would soon lead to their aggregation flocculation). This tendency, however, is counterbalanced by repulsive electrical forces between the particles. 

As lithogenic and biogenic particles are delivered to the coastal zone (via rivers and estuaries), they are exposed to many dynamic processes (e.g., aggregation, flocculation, desorption) that result in steep biogeochemical gradients on the continental shelf. 

The mechanism of protein haze formation in wines is not fully understood. Slow denaturation of wine proteins is thought to lead to protein aggregation, flocculation into a hazy suspension and, finally, formation of visual precipitates. The importance of non-proteinaceous factors in white wine protein haze formation such as proan-thocyanidins (Koch and Sajak 1959 Waters et al. 1995a Yokotsuka et al. 1991) have been suspected for some time. Other factors such as polysaccharides, alcohol levels and pH have also been implicated (Mesquita et al. 2001 Siebert et al. 1996a). It has been observed that grape protein added to model wine does not precipitate or produce haze when heated, whereas visually obvious hazes occur when the same protein is added to a commercial wine (Pocock 2006). 

Hollow to porous to void Ifee solid Singular, agglomerates, aggregates, flocculated materials... 

Is there assurance of stability of size in vitro, that is, lack of aggregation/flocculation ... 

Reversible flocculation of aqueous dispersions stabilized sterically with POE nonionics can be accomplished by increasing the temperature. With increase in temperature, the hydrogen bonding of the POE chains to water is reduced and the chains tend to aggregate, flocculating the dispersion. Upon reducing the temperature, the chains hydrate again and the particles redisperse. 

Other general trends that are described correctly by the model [42] include an increasing r (relative) with particle aggregation (flocculation) and the onset of solid-like behavior (the existence of a yield stress ) in some dispersions at low shear rates. 

Aggregation (flocculation) of solid particles, formation of large (flock-like) aggregates, contact of these aggregates with air bubbles and formation of a three-phase flotation foam. 

II. REVIEW OF ASPHALTENE CHEMISTRY, AGGREGATION, FLOCCULATION, AND SOLUBILITY... 

The exact composition of Stage I is found by experiment, to give the minimum grinding time and the most stable and complete dispersion. Stages II and III also require care, as hasty additions in an incorrect order can cause the pigment to re-aggregate (flocculate). 

It has already been noted that pharmaceutical suspensions in which a moderate particle-panicle aggregation (flocculation) takes place are useful because the open and spongy structure of the floes makes them easily redispersible the panicles funii an irregular network with appreciable amounts uf vehicle between theht. occupying almost the whole volume of the container (Fig. fl is an example). 

Aggregation, flocculation, and coagulation are terms used to describe the destabilization process when attractive forces interact between droplets only separated by a thin film of the continuous phase. For small interaction potentials, flocculation or aggregation will be reversed by rehomogenization similar to creaming and sedimentation. 

Ga is seen to increase very sharply with decreasing h when the latter reaches small values. In the absence of repulsion between the particles or droplets, the latter will aggregate (flocculate) by simple diffusion through the medium. This leads to fast flocculation kinetics and the rate constant for the process ko has been calculated using the Smolulokowski equation,... 

Free-disperse systems comprise dilute emulsions, sols, and suspensions in which the participation of particles in thermal Brownian motion plays a dominant role over the cohesive forces between them. In these systems, we are particularly interested in the stability resisting the transition from the free-disperse state to the connected-disperse state via aggregation, flocculation, or sedimentation (Figure 4.2). 

In general there are three coupled sub-processes that will influence the rate of breakdown processes in emulsions. These are aggregation (Flocculation), coalescence and phase separation (i ). Figure 3. They will be discussed in some details. 

The response of PEC particles, formed in pure water, to the addition of low molecular salts may be very different. Aggregation, flocculation, swelling and... 

In addition to the common instability of multiple emulsions, there are two instabilities related to polymeric surfactants. The common destabilization mechanisms are demonstrated in Figure 5.6 and include aggregation, flocculation, and coalescence (Mezzenga et al., 2004). 

Multiple emulsions made of low-molecular-weight emulsifiers (the so-called monomeric emulsifiers) are mostly unstable thermodynamically. This is mainly because in the second stage of the emulsification severe homogenization or shear are not recommended, and as a result large droplets are obtained. During years of research attempts have been made to find proper and more suitable combinations of emulsifiers to reduce droplets sizes and to improve the emulsion stability. Aggregation, flocculation, and coalescence (occurring in the inner phase and between the multiple-emulsion droplets) lead to rupture of droplets and separation of the phases and thus are major factors behind the instability of the emulsions. 

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