Colloidal Suspension Stability

Colloidal suspensions stabilized by electrostatic repulsion are very sensitive to any phenomenon able to disrupt the double layer like ionic strength or thermal motion. 

Wilson. B.A. and Crimp, M.J.. Prediction of composite colloidal suspension stability based upon the Hogg, Healy, and Fuerstenau inteipretation, Langmuir, 9, 2836, 1993. 

The remainder of this contribution is organized as follows. In section C2.6.2, some well studied colloidal model systems are introduced. Methods for characterizing colloidal suspensions are presented in section C2.6.3. An essential starting point for understanding the behaviour of colloids is a description of the interactions between particles. Various factors contributing to these are discussed in section C2.6.4. Following on from this, theories of colloid stability and of the kinetics of aggregation are presented in section C2.6.5. Finally, section C2.6.6 is devoted to the phase behaviour of concentrated suspensions. 

Many properties of colloidal suspensions, such as their stability, rheology, and phase behaviour, are closely related to the interactions between the suspended particles. The background of the most important contributing factors to these interactions is discussed in this section. 

In many colloidal systems, both in practice and in model studies, soluble polymers are used to control the particle interactions and the suspension stability. Here we distinguish tliree scenarios interactions between particles bearing a grafted polymer layer, forces due to the presence of non-adsorbing polymers in solution, and finally the interactions due to adsorbing polymer chains. Although these cases are discussed separately here, in practice more than one mechanism may be in operation for a given sample. 

Behrens S H, Borkovec M and Schurtenberger P 1998 Aggregation in charge-stabilized colloidal suspensions revisited Langmuir 1951-4... 

Many precipitates, such as Fe(OH)3, form initially as colloidal suspensions. The tiny particles are kept from settling out by Brownian motion, the motion of small particles resulting from constant bombardment by solvent molecules. The sol is further stabilized by the adsorption of ions on the surfaces of the particles. The ions attract a layer of water molecules that prevents the particles from adhering to one another. 

The deposition of similar charges on the particles of a colloidal suspension is important in achieving stability of the suspension. The similarly charged particles repel each other, minimizing aggregation. 

Mevellec, V., Roucoux, A., Ramirez, E., Philippot, K. and Chaudret, B. (2004) Surfactant-stabilized aqueous iridium(O) colloidal suspension an effident reusable catalyst for hydrogenation of arenes in biphasic media. Advanced Synthesis and Catalysis, 346 (1), 72-76. 

Determine the minimum amount of protein A required to stabilize the colloidal gold sol being used. The colloidal suspension should be adjusted, if needed, with 0.1M K2CO3 to pH 6-7. Measure the pH of the sol using a gel-filled electrode. Determining the stabilization amount of protein A can be done according to the method described in Section 1, this chapter. 

Ammonium salts are commonly used to stabilize aqueous colloidal suspensions of nanoparticles. The first such example was reported in 1983-84 by Januszkie-wicz and Alper [96, 97], who described the hydrogenation of several benzene derivatives under 1 bar H2 and biphasic conditions starting with [RhCl(l,5-hexa-diene)]2 as the metal source and with tetraalkylammonium bromide as a stabilizing agent Some ten years later, Lemaire and coworkers investigated the cis/... 

Although several noble-metal nanoparticles have been investigated for the enantiomeric catalysis of prochiral substrates, platinum colloids remain the most widely studied. PVP-stabilized platinum modified with cinchonidine showed ee-values >95%. Several stabilizers have been also investigated such as surfactants, cinchonidinium salts and solvents, and promising ee-values have been observed. Details of a comparison of various catalytic systems are listed in Table 9.16 in one case, the colloid suspension was reused without any loss in enantioselectiv-ity. Clearly, the development of convenient two-phase liquid-liquid systems for the recycling of chiral colloids remains a future challenge. 

Poly(styrene)-poly(acrylate) colloidal suspensions, 7 275 Polystyrene/polyfmethyl methacrylate) commercial block copolymers, 7 648t Polystyrenes. See also Polystyrene (PS) commercial, 23 364 general-purpose, 23 364 specialty, 23 364-366 stabilized, 23 366 tactic, 23 365... 

The synthesis of silica membranes has only recently been described. Silica forms sols and gels very easily both by the colloidal suspension and by the polymeric gel route. Its chemical resistance and its thermal stability in the presence of water vapor or metal impurities are not very good however. Larbot et al. (1989) have described the synthesis of silica membranes starting with a commercially available silica sol (Cecasol Sobret) in an aqueous solution at pH 8. 

Stabilizer. (1) A fractionating column used to remove light gases from a material that is otherwise liquid at ambient temperatures (2) A compound capable of keeping another compound, mixture, or solution from changing its chemical nature a stabilizer can slow down a chemical reaction, keep components in emulsion form, or keep particles in a colloidal suspension from precipitating. 

Clay minerals have a permanent negative charge due to isomorphous substitutions or vacancies in their structure. This charge can vary from zero to >200cmol kg" (centimoles/kg) and must be balanced by cations (counter-ions) at or near the mineral surface (Table 5.1), which greatly affect the interfacial properties. Low counter-ion charge, low electrolyte concentration, or high dielectric constant of the solvent lead to an increase in interparticle electrostatic repulsion forces, which in turn stabilize colloidal suspensions. An opposite situation supports interparticle... 

It is operationally difficult to distinguish between dissolved and colloidally dispersed substances. For example, colloidal metal-ion precipitates occasionally have particle sizes smaller than 100 A, sufficiently small to pass through a membrane filter, and organic substances can exist as a stable colloidal suspension. Information on the types of species encountered under different chemical conditions (type of complexes, their stabilities, rate of formation) is a prerequisite to better understanding of the transformation in properties of toxic chemicals in a water body. 

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