Colloidal particles Effects

Duran, J.D.G. Gonzallez-Caballero, E. (2000) Stability of cobalt-ferrite colloidal particles. Effect of pH and applied magnetic field. Langmuir 16 7954-7961 De Vitre, R. Belzile, N. Tessier, A. (1991) Spe-ciation and adsorption of arsenic on diage-netic iron oxyhydroxides. Limnol. Oceanogr. 36 1480-1485... 

Ilium, L., Davis, S. S., Wilson, C. G., Thomas, N. W., and Frier, M. (1982) Blood clearance and organ deposition of intravenously administered colloidal particles. Effects of particle size, nature and shape, Int. J. Pharm., 12 135-146. 

Ohshima, H., Electrophoretic mobibty of polyelectrolyte-adsorbed colloidal particle effect of segment distribution, J. Colloid Interface ScL, 185, 269, 1997. 

Janca, J. Micro-thermal field-flow fractionation of colloidal particle Effect of temperature on retention and relaxation processes. CoU. Czech. Chem. Commun. 2003, 68, 672. Janca, J. Bemeron, J.-R Boutin, R. Micro-thermal field-flow fractionation New high-performance method for particle size distribution analysis. J. Coll. Interf. Sci. 2003,260, 317. Janca, J. Micro-channel thermal field-flow fractionation High-speed analysis of colloidal particles. J. Liq. Chromatogr. Relat. Technol. 2003, 26, 849. 

Particularly in polar solvents, electrostatic charges usually have an important contribution to tire particle interactions. We will first discuss tire ion distribution near a single surface, and tlien tire effect on interactions between two colloidal particles. 

More sophisticated approaches to describe double layer interactions have been developed more recently. Using cell models, the full Poisson-Boltzmann equation can be solved for ordered stmctures. The approach by Alexander et al shows how the effective colloidal particle charge saturates when the bare particle charge is increased [4o]. Using integral equation methods, the behaviour of the primitive model has been studied, in which all the interactions between the colloidal macro-ions and the small ions are addressed (see, for instance, [44, 45]). 

The second case involves non-adsorbing polymer chains in solution. It was realized by Asakura aird Oosawa (AO) [50] aird separately by Vrij [51] tlrat tlrese chains will give rise to air effective attraction between colloidal particles. This is kirowir as depletion attraction (see figure C2.6.4. We will summarize tire AO tlreory to explain tlris. 

In extensively deionized suspensions, tliere are experimental indications for effective attractions between particles, such as long-lived void stmctures [89] and attractions between particles confined between charged walls [90]. Nevertlieless, under tliese conditions tire DLVO tlieory does seem to describe interactions of isolated particles at tire pair level correctly [90]. It may be possible to explain tire experimental observations by taking into account explicitly tire degrees of freedom of botli tire colloidal particles and tire small ions [91, 92]. 

Colloidal suspensions are systems of small mesoscopic solid particles suspended in an atomic liquid [1,2]. We will use the term colloid a little loosely, in the sense of colloidal particle. The particles may be irregularly or regularly shaped (Fig. 1). Among the regular shapes are tiny spherical balls, but also cylindrical rods or flat platelets. As the particles are solid, fluctuations of their form do not occur as they do in micellar systems. Not all particles in a suspension will, in general, have the same form. This is an intrinsic effect of the mesoscopic physics. Of course in an atomic system, say silicon, all atoms are precisely similar. One is often interested in the con-... 

The world of colloidal particles is large and fasdnating. Basic simulation techniques rapidly lead to challenging questions and new things to be discovered. Computer simulations are close enough to experiments to allow intellectual inspiration as well as a quantitative comparison of the results. We have reviewed the basic simulation techniques and their principal implementation but could only briefly mention advanced techniques and results. A survey of the recent literature shows the variety of physical effects present in colloidal systems and accessible to computer simulations. 

Comprehension of the interactions among microstructures composed of tethered chains is central to the understanding of many of their important properties. Their ability to impart stability against flocculation to suspensions of colloidal particles [52, 124, 125] or to induce repulsions that lead to colloidal crystallization [126] are examples of practical properties arising from interactions among tethered chains many more are conceivable but not yet realized, such as effects on adhesion, entanglement or on the assembly of new block copolymer microstructures. We will be rather brief in our treatment of interactions between tethered chains since a comprehensive review has been published recently of direct force measurements on interacting layers of tethered chains [127]. 

Electroviscous effect occurs when a small addition of electrolyte a colloid produces a notable decrease in viscosity. Experiments with different salts have shown that the effective ion is opposite to that of the colloid particles and the influence is much greater with increasing oxidation state of the ion. That is, the decrease in viscosity is associated with decreased potential electrokinetic double layer. The small amoimt of added electrolyte can not appreciably affect on the solvation of the particles, and thus it is possible that one of the determinants of viscosity than the actual volume of the dispersed phase is the zeta potential. 

Liu, J Kim, AY Virden, JW Bunker, BC, Effect of Colloidal Particles on the Eormation of Ordered Mesoporous Materials, Langmuir 11, 682, 1995. 

Ohshima, H Kondo, T, Electrophoretic Mobility and Donnan Potential of a Large Colloidal Particle with a Surface Charge Layer, Journal of Colloid and Interface Science 116, 305, 1987. O Neil, GA Torkelson, JM, Modeling Insight into the Diffusion-Limited Cause of the Gel Effect in Free Radical Polymerization, Macromolecules 32,411, 1999. 

Hydrophobic colloidal particles move readily in the liqnid phase under the effect of thermal motion of the solvent molelcnles (in this case the motion is called Brownian) or under the effect of an external electric field. The surfaces of such particles as a rule are charged (for the same reasons for which the snrfaces of larger metal and insnlator particles in contact with a solution are charged). As a result, an EDL is formed and a certain valne of the zeta potential developed. 

As at other interfaces, the effective snrface charge of colloidal particles depends on the total concentration and composition of the solution, particnlarly on polyvalent or snrface-active ions that may be present. When the zeta potential is reduced below a certain critical (absolute) value, which is approximately 25 to 30 mV, the colloidal solution becomes nnstable. 

The presence of shielding compounds interferes with subsequent processes, as the formation of metal-support interactions is able to stabilize supported particles. Moreover, the shielding effect of the colloid protectors prevents the contact of metal particles with the reacting molecules, thus avoiding the use of unsupported colloidal particles as a catalytic system [11]. 

Different from the metal concentration, the content of water in the reaction system exhibits an obvious effect on the particle size of the resulted metal nanoclusters. In a mixture of EG and water (10 1 in volume ratio), Pt hydroxide colloidal particles formed in the first synthesis step were 4.0 nm in average diameter, and the finally obtained Pt nanoclusters had an average particle size of... 

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

The yield of the photocathodic dissolution of CdS in a solution containing 1 x 10" M SOi" is only 0.005 molecules dissolved per photon absorbed. In the presence of 5 X 10 M excess Cd " ions it amounts to 0.05. Sulfate and dithionate are formed in the ratio 2.2 to 1. The oxidation of SO3" is effected by the positive holes produced upon illumination, two holes being necessary to convert one SO ion into SO " or 1/2 SjOg . If the SOj anion captured the two holes from the same colloidal particle ( two-hole mechanism ), only sulfate would appear as the oxidation product. However, if SO3" captured only one hole to form the radical SOj", the final products would be formed bj reactions of two such radicals, and these two radicals could even originate from different colloidal particles ( one-hole mechanism )... 

Differences in the absorption spectra of colloidal and macrocrystalline semiconductors were first recognized for CdS and AgBr The absorption of 3 nm particles of CdS in aqueous solution begins close to 515 nm, the wavelength at which bulk CdS starts to absorb however, the increase in absorption at shorter wavelengths is much less steep than for the macrocrystalline material (Fig. 6). The effect was first explained by a possible amorphous structure of the colloidal particles However, after it was shown by Brus and co-workers that the particles had an ordered struc-... 

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