Colloids/colloidal

In the previous section, non-equilibrium behaviour was discussed, which is observed for particles with a deep minimum in the particle interactions at contact. In this final section, some examples of equilibrium phase behaviour in concentrated colloidal suspensions will be presented. Here we are concerned with purely repulsive particles (hard or soft spheres), or with particles with attractions of moderate strength and range (colloid-polymer and colloid-colloid mixtures). Although we shall focus mainly on equilibrium aspects, a few comments will be made about the associated kinetics as well [69, 70]. 

Grieser F, Ashokkumar M (2004) In Caruso F (ed) Sonochemical synthesis of inorganic and organic colloids, colloids and colloid assemblies. Wiley-VCH GmbH Co. KgaA, Weinheim, pp 120-149... 

Fig. 7.1 gives a size spectrum of water-borne particles. Particles with diameters less than 10 pm have been called colloids. In soils, the clay-sized and fine silt-sized particles are classified as colloids. Colloids do not dissolve, but instead remain as a solid phase in suspension. Colloids usually remain suspended because their gravitational settling is less than 10 2 cm s 1. Under simplifying conditions (spherical particles, low Reynolds numbers), Stokes law gives for the settling velocity, vs... 

Phytoplankton, biological debris, humus colloids (colloidal humic acid), fibrils ... 

As described in Section 3 of Chapter 2, multi-electron processes are important for designing conversion systems. Noble metals are most potent catalysts to realize a multi-electron catalytic reaction. It is well known that the activity of a metal catalyst increases remarkably in a colloidal dispersion. Synthetic polymers have often been used to stabilize the colloids. Colloidal platinum supported on synthetic polymers is attracting notice in the field of photochemical solar energy conversion, because it reduces protons by MV to evolve H2 gas.la)... 

Colloidal Dispersions or Solutions (Sols) and Colloids. Colloidal solutions (or rather "pseudo solutions ), also called sols (or in case of liquids hydrosols) are heterogeneous systems consisting of a "dispersion medium (mostly a liquid) and a "dispersed or "suspended medium known as a "colloid . Colloidal particles are invisible under ordinary microscope but detectable by the ultramicroscope. Their size ranges from ca 1 x 10 7 to 1 x 5 smm. If the dispersion is a viscous, sticky, transparent liquid, it is what is generally known as a "colloidal solution . As examples of this may be cited a soln of gum-arabic in water and sol ns of NC in acetone, ethyl acetate or ether alcohol. When "solns are dialized, most of the colloidal particles do not pass thru the membrane. This is their principal distinction from "crystalloids , which are substances like Na chloride, etc. If part of the volatile liquid (dispersing medium), is evaporated the resulting tacky, jellylike substance is known as a gel. 

Gels, sols, foams and emulsions are all examples of mixtures which are formed by mixing two substances (or phases) which cannot mix. These mixtures are often referred to as colloids. Colloids are formed if the suspended particles are between 1 nm and 1000nm in size (lnm = 1 x 10 9m). 

Colloids. Colloids include particles with hydrophobic, hydrophilic and intermediate forms with a size range 1 - 400 nm. Both organic (including macromolecules) and inorganic (hydrolyzed silica and metal oxides) colloids occur in the marine environment (Sigleo and Helz, 1981). Their surfaces often contain suitable sites for interactions with trace metals (adsorption, complexation). In the marine environment all particles have a negative surface charge (Neihof and Loeb, 1972 Hunter and Liss, 1982). Increase of the electrolyte concentration decreases the stability of the colloidal particles. As a result the... 

Landfester, K. Antonietti, M. Miniemulsions for the convenient synthesis of organic and inorganic nanoparticles and single molecule applications in materials chemistry. Colloids Colloid. Assembl., 175-215 (2004). 

A substance which passes into the colloidal state, simply by bringing it in contact with water is known as hydrophilic colloid (hydro = water, philic = loving). But if any solvent like organic liquid is used instead of water, then the more general term lyophilic colloid (lyo = solvent philic = loving) is used. Gum, starch, soap are lyophilic colloids. These colloids when once precipitated can again be brought back directly into the colloidal state. Hence, they are also known as reversible colloids. (Colloidal state precipitate). Reversible colloids are also termed as resoluble or non-electrocratic colloids. 

Substances like metals, metal sulphides cannot be brought into the colloidal state simply by bringing them in contact with water and, therefore, special methods are devised for the purpose. Hence, they are known as hydrophobic colloids (hydro = water phobic = hating). In case of solvent other than water, the general term lyophobic is used. Further, if these colloids are precipitated, then it is not very easy to reconvert the precipitate directly into the colloidal state. Hence, they are termed as irreversible colloids (colloidal state — precipitate), irresoluble or electrocratic colloids. 

Graham [3] defined a colloidal dispersion in 1861 and he also defined the range of size for colloidal particles by two observations. The lower limit was determined by the slow diffusion of colloids in a dispersion, which indicated a particle size larger than 1 nm. The upper limit of the colloidal size is given by the slow rate of sedimentation under normal gravity. His conclusion was that molecules could not be larger than a 1 / n. Today particles which have a size, at least in one dimension, of 1 nm-10 /im are called colloids. Colloidal solutions can be divided into three classes [1,8]. 

Many of these food systems are dispersions that belong in the realm of colloids. Colloids are defined as heterogeneous or dispersed systems that contain at least two phases—the dispersed phase and the continuous phase. Colloids are characterized by their ability to exist in either the sol or the gel form. In the former, the dispersed particles... 

Sorption to Organic Colloids Colloidal organic material (e.g., humic colloids) absorbs nonpolar organic chemicals. Operationally, an increase of ap-... 

Particles in a suspension are much larger than atoms. In contrast, particles in a solution are atomic-scale in size. A heterogeneous mixture of intermediate size particles (between the size of solution particles and suspension particles) is a colloid. Colloid particles are between 1 nm and 1000 nm in diameter. The most abundant substance in the mixture is the dispersion medium. Milk is a colloid. Although homogenized milk resembles the cornstarch mixture in Figure 15-19a, you cannot separate its components by settling or by filtration. 

Metal particles of diameters in the size range of approximately 10-100 nm are usually called colloids. Colloids normally show more or less broad size distributions and are characterized by a polycrystalline structure like the bulk materials. Clusters can roughly be defined as being built up by a distinct number of ordered atoms. These conditions are mostly realized in particles smaller than 3>-A nm. In between there exists a region where particles may be considered to be clusters as well as colloids because of the lack of a precise borderline. 

Colloids Colloids are volume expanders that increase the patient s fluid volume. These are ... 

HydrophUic colloids Colloidal particles that attract water molecules. 

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