Dispersion state

A colloid is a material that exists ia a finely dispersed state. It is usually a solid particle, but it may be a Hquid droplet or a gas bubble. Typically, coUoids have high surface-area-to-volume ratios, characteristic of matter ia the submicrometer-size range. Matter of this size, from approximately 100 nm to 5 nm, just above atomic dimensions, exhibits physicochemical properties that differ from those of both the constituent atoms or molecules and the macroscopic material. The differences ia composition, stmcture, and iateractions between the surface atoms or molecules and those on the iaterior of the colloidal particle lead to the unique character of finely divided material, specifics of which can be quite diverse (see Flocculating agents). 

Figure 18-82 illustrates the relationship between solids concentration, iuterparticle cohesiveuess, and the type of sedimentation that may exist. Totally discrete particles include many mineral particles (usually greater in diameter than 20 Im), salt crystals, and similar substances that have httle tendency to cohere. Floccnleut particles generally will include those smaller than 20 [Lm (unless present in a dispersed state owing to surface charges), metal hydroxides, many chemical precipitates, and most organic substances other than true colloids. 

Ishihara K, Shibata N, Tanaka S, Iwasaki Y, Kurosaki T, and Nakabayashi N. Improved blood compatibility of segmented polyurethane by polymeric additives having phospholipids polar group. U. Dispersion state of polymeric additive and protein adsorption on the surface. J Biomed Mater Res, 1996, 32(3), 401 18. 

Figure 1 is a TEM photograph of the Cu (10wt%)/Al2O3 catalyst prepared by water-alcohol method, showing the dispersed state of copper and was confirmed the particle sizes from XRD data. Figure 2 is X-ray diffraction patterns of above-mention catalysts, was used to obtain information about phases and the particle size of prepared catalysts. Metal oxide is the active species in this reaction. Particle sizes were determined fix)m the width of the XRD peaks by the Debye-Scherrer equation. 

Electrochemical processes in melts are often attended by side reactions and phenomena complicating the primary process. This is true, in particular, for the technically very important class of reactions in which a number of metals (calcium, barium, and others) are obtained electrometallurgically from molten salts. In many of these processes the metal that is deposited (sometimes in a highly disperse state) is found to interact with the corrosive melt for example, in a reaction such as... 

For higher efficiency in catalytic action and smaller quantitative needs, the catalysts often are used in a highly disperse state. An important practical criterion for such catalysts is the specific reaction rate [i.e., the reaction rate per unit mass of the catalyst... 

Most often, these disperse metal catalysts are supported by an electronically conducting substrate or carrier that should provide for uniform supply or withdrawal of electrons (current) to or from all catalyst crystallites. The substrate should also serve to stabilize the disperse state of the catalyst and retard any spontaneous coarsening of the catalyst crystallites. Two situations are to be distinguished (1) the disperse metal catalyst is applied to a substrate consisting of the same metal, and (2) it is applied to a chemically different substrate (a foreign substrate). Platinized platinum is a typical example of the former situation. 

Electrophoresis can be observed in solutions containing suspended matter (solid parhcles, liquid drops, gas bubbles) in a highly disperse state (Fig. 31.2a). Under the influence of an electric held, these particles start to be displaced in the direchon of one of the electrodes. Often, this movement is toward the negative electrode or cathode hence, electrophoresis has occasionally been called cataphoresis. 

Several factors are associated with the difficulty in assessing CNT toxicity. Among them, CNT interactions with components of the dispersing medium, the cytotoxicity assay employed, impurities, CNT surface chemistry, and dispersion state are the... 

An interesting question comes up in connection with psychotic patients suffering from dementia praecox catatonia. The psychosis is due unquestionably to an over-dispersed state, and we must therefore conclude either that the sleep of such patients is theoretically quite different from ordinary sleep or that the centers of consciousness may be over-agglomerated while some centers of thinking are over-dispersed. So far as I can learn, these patients do sleep normally as a rule. Consequently one portion of the brain must be over-agglomerated at times, even though another portion of the brain is over-dispersed. 

Si02 catalyst because XRD and EXAFS peaks observed for calcined Co(5)/ CyDTA/Si02 are negligible or much weaker than those for calcined Co(20)/SiO2. However, this was not observed in the present study, and Co304 species were in a more dispersed state on the calcined Co(20)/CyDTA/SiO2 catalyst. 

Whichever method is followed, a protective agent able to induce a repulsive force opposed to the van der Waals forces is generally necessary to prevent agglomeration of the formed particles and their coalescence into bulk material. Since aggregation leads to the loss of the properties associated with the colloidal state, stabilization of metallic colloids - and therefore the means to preserve their finely dispersed state - is a cmcial aspect for consideration during their synthesis. 

Mists Suspended liquid droplets generated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state such as by splashing, foaming, or atomizing. Mist is formed when a finely divided liquid is suspended in air. 

To keep the precipitating polymers in the dispersed state throughout the polymerization, requires steric stabilizers. This problem is classically tackled via copolymerization with fluoroalkylmethacrylates or the addition of fluorinated surfactants, both being only weak steric stabilizers. DeSimone el al. also applied a fluorinated block copolymer,9 proving the superb stabilization efficiency of such systems via a rather small particle size. One goal of the present chapter is therefore an investigation of our fluorinated block copolymers as steric stabilizers in low-cohesion-energy solvents. 

The surface active agents (surfactants) may be cationic, anionic or non-ionic. Surfactants commonly used are cetyltrimethyl ammonium bromide (CTABr), sodium lauryl sulphate (NaLS) and triton-X, etc. The surfactants help to lower the surface tension at the monomer-water interface and also facilitate emulsification of the monomer in water. Because of their low solubility surfactants get fully dissolved or molecularly dispersed only at low concentrations and at higher concentrations micelles are formed. The highest concentration where in all the molecules are in dispersed state is known as critical micelle concentration (CMC). The CMC values of some surfactants are listed in table below. 

The hydrothermal carbons obtained in the end from soluble, non-structural carbohydrates are micrometer sized, spherically shaped particle dispersions, containing a sp2 hybridized backbone (also responsible for the brown to black color) decorated with a dense layer of polar oxygenated functionalities still remaining from the original carbohydrate. The presence of these surface groups offers the possibility of further functionalization and makes the materials more hydrophilic and well-dispersible in water. The size of the final particles depends mainly on the carbonization time and precursor concentration inside the autoclave, as well as additives and stabilizers potentially added to the primary reaction recipe. An SEM image of a model reaction illustrating this dispersion state is shown in Fig. 7.1. 

Emulsions are colloidal suspensions produced by combining two liquids, and their dispersed state is usually stabilized by yet another component, termed an emulsifying agent. Foams are gaseous colloidal suspensions formed by combining two substances (of which one is typically a gas), and again the stability of a foam is aided... 

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