Dispersion and aggregation

Colloidal particles in suspension can be induced to aggregate by adding additional, smaller particles to the same solution. Explain this phenomenon. 

Suggest two reasons why silt (suspended clay particles) deposits form at the mouth of a river delta. 

Show that the terminal velocity for sedimentation of colloidal spherical particles in a Newtonian fluid can be given by the equation 

Calculate the Debye screening length for a charged particle of radius 300 nm when dispersed in a 1 Af NaCl aqueous solution at room temperature. How would your result change if MgCl2 was used instead  

How long will it take 200-nm particles added to one side of a 30-cm long horizontal pipe filled with water to diffuse to the other end in the absence of a flow Make your estimate using the Stokes-Einstein relation. 

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FIGURE 29.4 Filler aggregation and dispersion. (From Li, Y. et al.. Rubber Chem. TechnoL, 67, 693, 1994.)... 

In animal species commonly used in laboratory research, social aggregation and dispersion are achieved by agonistic behavior patterns with various acts, postures, movements, and signals. Confrontations between a territorial resident and an intmder, between a dominant and lower-ranking group member, between rival males or females, between a lactating female and a... 

Knutton, S., Shaw, R. K., Anantha, R. P., Donnenberg, M. S., and Zorgani, A. A. (1999). The type rV bundle-forming pilus of enteropathogenic Escherichia coli undergoes dramatic alterations in structure associated with bacterial adherence, aggregation and dispersal. 

The apparent viscosity of a system which thins on shearing is most susceptible to changes in the shear rate in the intermediate range where there is a balance between randomness and alignment, and between aggregation and dispersion. 

Perhaps the most common method for preparing polymer-nanotube composites has been to mix the nanotubes and polymer in a suitable solvent before evaporating the solvent to form a composite film. One of the benefits of the solution casting method is that agitation of the nanotube powder in a solvent facilitates nanotube de-aggregation and dispersion. Almost all solution processing methods are variations on a general theme which can be summarized in three major steps ... 

In general, de-aggregation and dispersion of carbon nanotubes are provided by magnetic stirring, shear mixing, reflux, or, most commonly, ultrasonication. Sonication can be provided in... 

BORDEN, J.H., Semio-Chemical Mediated Aggregation and Dispersion in the Coleoptera. Academic Press, London, 1984. 

Patterson, R. G., 1971, Aggregation and dispersal behavior in captive Gopherus agassizi, J. Herpetol., 5 214. 

Figure 2. A) Normally dispersed CEM cells are aggregated by GaUl (10 pM). B) Titration of neoglycocluster 1 in the presence of CEM cells and 10 pM Gal-1 (i) at 200 pM 1 cells are aggregated, (ii) at 300 pM 1 cells are aggregated, (Hi) at 400 pM 1 cells are aggregated, (iv) at 500 pM 1 cells are in the mixed state of small aggregates and dispersed cells, (v) at 600 pM 1 cells are in the mixed state, (vi) at 700 pM 1 cells are dispersed.

Kumar R, Antolino N, Wichard JE, Sutovich KJ, Chapman DM, Roberie TG, et al. Optimized de-aggregation and dispersion of high concentration slurry of nanophase alumina by chemically aided attrition milling. Working paper, 2005. 

Eder G, Janeschitz-Kriegl H (1997) CrystallizatioiL In Meijer HEH (ed) Materials seience and technology, processing of polymers, vol 18. Wiley-VCH, New York, pp 189-268 Eduljee RF, McCullough RL, Gillespie JW Jr (1994) The influence of aggregated and dispersed textures on the elastic poperties of discontinuous-fiber composites. Compos Sci Technol 50 381-391... 

Smart particles capable of reversible transition between aggregated and dispersed states were used for affinity precipitation of proteins. Thermosensitive (44) or pH-sensitive latices (45) or salt-sensitive liposomes that have polsrmerized membranes (35) are examples of such systems. 

Joseph, D. D., Y. J. Liu, M. Poletto and J. Feng, Aggregation and dispersion of spheres falling in viscoelastic liquids, J. Non-Newtonian Fluid Mech. 54 45-86 (1994). 

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