Flocculation phenomenon

The flocculating properties of resins from barium ferrite and y-iron oxide are similar. Even diough the magnetized resin is flocculated, the floes break up readily when stirred so that the particles react more rapidly than standard-sized resin beads which are 300-1200 pm in diameter (Fig. 2). The shell configuration of whisker-type resins also enhances reaction r tes. Because of the magnetic flocculation phenomenon the magnetized beads separate out much more rapidly than the unmagnetized ones (Fig. 3). 

Although eq. (49) appears to show all essential features to describe the- flocculation phenomenon as a function of the system, and, as a first approximation, gives quite satisfactory results, most of our calculations have been done according to the second method, in which the approximate eq. (43) is substituted by the exact values of as obtained from Table XT. To this end we applied the graphic method mentioned above. We determined graphically, for a given value of A, a number... 

The authors suggested that crowding factor could be a useful tool for characterizing the flocculation potential of different pulps. Table 2.4 represents the meaning of this parameter for prediction of the flocculation phenomenon. 

Since the emulsions stabilities for this oil-phase only were not sufficiently high to achieve reliable results, asphaltenes precipitated from crude A were added to the model emulsions in the same amount as in the actual crude oU. Figures 12.7 and 12.8 show the viscosity ratio as a function of particle concentration for the model emulsions stabilized with very hydrophobic and mildly hydrophilic silica particles, respectively. Model oil and crude oil emulsions show many similarities. For all model emulsions the stability in the absence of particles is lower, because the absolute viscosity is much lower than the one encountered in crude oil emulsions. Consequently, the effect of the shear rate on the destabilization is more pronounced. However, as particles are added in larger amounts, crude oil and model oil emulsions behave in the same way. Nevertheless, in Figure 12.8 the viscosity ratios are shifted towards lower values since a strong flocculation phenomenon enhanced by the low viscosity of the samples brings coalescence. 

Ideally one would like a continuous reactor system to operate indefinitely at the desired steady-state. Unfortunately, a number of factors can cause shorter runs. Formation of wall polymer and latex flocculation is one such problem. This phenomenon can reduce reactor performance (for example, loss of heat transfer), lower product quality, and shorten run time. 

Another electrical measurement useful in detecting flocculation in aniso-metric particles is the response of dielectric constant to shear. The alignment along streamlines of flow which results from laminar shear in a viscometer decreases the dielectric constant of the system if the dipole moment lies along the long axis of the particle. Another way in which this phenomenon can be meas-... 

This paper reviews the experiences of the oil industry in regard to asphaltene flocculation and presents justifications and a descriptive account for the development of two different models for this phenomenon. In one of the models we consider the asphaltenes to be dissolved in the oil in a true liquid state and dwell upon statistical thermodynamic techniques of multicomponent mixtures to predict their phase behavior. In the other model we consider asphaltenes to exist in oil in a colloidal state, as minute suspended particles, and utilize colloidal science techniques to predict their phase behavior. Experimental work over the last 40 years suggests that asphaltenes possess a wide molecular weight distribution and they may exist in both colloidal and dissolved states in the crude oil. 

Deep shades of maroon tend to form water spots in certain binder systems, especially in media which are based on acrylic resin. More or less distinctive light spots appear on the coating. The effects that cause this phenomenon remain to be elucidated. Factors such as long-term weathering at elevated temperature, U V radiation, and the presence of demineralized water probably cause reduction and solvation effects within the coating. Products are available which are much less susceptible to these agents. Rub-out effects, especially flocculation, may also present problems in various binder systems. Special-purpose grades are therefore available which are more stable to flocculation. 

Yeast flocculation mechanism can be described as a phenomenon of adhesion to certain surfaces. The ability to adhere to surfaces and to form biofilm is the basis of the pathogenicity of Candida species. Pathogens adhere to mucous membranes and wounds, they stick to medical instruments and prosthesis, and thus contaminate surfaces in food processing facilities. The high mortality rate in disseminated fungal infections caused an increase in the amount of research on the molecular basis of the adhesive phenomena in Candida. This research discovered a considerable overlap in the molecular regulation of all forms of adhesive behavior. ... 

Flocculins and especially Flo 11 are responsible for morphogenic phenomena such as pseudohyphal growth and biofilm formation in yeast. Biofilm formation is an adhesive phenomenon akin to flocculation. The majority of bacteria exist in highly organized natural biofilm populations rather than in free floating cultures. Within the biofilm, bacteria display coordinated behavior. They form structures, release toxins or emit light. They, sometimes, differentiate to form physiologically defined... 

In the case of biopolymer molecules residing in the space between colloidal particles or droplets, the force associated with the deep energy minimum at contact is often referred to as the depletion force because the intervening biopolymer species are depleted from the narrow gap between the pair of neighbouring particles. This attractive interparticle interaction underlies the phenomenon of reversible depletion flocculation in oil-in-water emulsions (see equation (3.41) in chapter 3). 

Another interesting phenomenon is that of depletion flocculation. This can be observed with dispersions (e.g. lattices) which contain inert additives, such as free polymer, non-ionic surfactant or even small (e.g. silica) particles. As the latex particles approach one another, the gaps between them become too small to accommodate the above additives, but the kinetic energy of the particles may be sufficient to enable them to be expelled from the gap i.e. a de-mix occurs, for which AG is positive. When this de-mix has been achieved, an osmotic situation exists in which the remaining pure dispersion medium will tend to flow out from the gap between the particles in order to dilute the bulk dispersion medium, thus causing the particles to flocculate. 

Small quantities of polysaccharides can flocculate a dispersed phase through bridging (Ward-Smith, et al., 1994), whereby one attached molecule with other adsorption sites along it may attach itself to another or more surfaces, acting as the bridge this phenomenon is called bridging flocculation. A bridge may instead cause steric stabilization of the dispersed phase. In the view of van Oss (1991), steric stabilization is predominantly a polar repulsion between macromolecules that is influenced not by Brownian activity, but by osmosis. 

The experiments with aqueous dispersions (4) indicated a somewhat different behavior, both with respect to the initial rate of flocculation and the equilibrium state. The initial rate of flocculation increased from zero to a maximum value and decreased to zero as the free polymer concentration was further increased, indicating restabilization at higher concentrations. The amount of floe phase formed has also been observed to go through a maximum with increasing free polymer concentration. The restabilization phenomenon at higher polymer concentrations could not be detected in nonaqueous dispersions (1-3). 

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