Colloids dimensions

J) The extreme fineness of iadividual clay particles, which may be of colloidal size ia at least one dimension. Clay minerals are usually platy ia shape, and less often lathlike and tubular or scroU shaped (13). Because of this fineness clays exhibit the surface chemical properties of coUoids (qv) (14). Some clays possess relatively open crystal lattices and show internal surface colloidal effects. Other minerals and rock particles, which are not hydrous aluminosihcates but which also show colloidal dimensions and characteristics, may occur intimately intermixed with the clay minerals and play an essential role. 

Let us add here that the fabrication of polycrystalline semiconductive films with enhanced photoresponse and increased resistance to electrochemical corrosion has been attempted by introducing semiconductor particles of colloidal dimensions to bulk deposited films, following the well-developed practice of producing composite metal and alloy deposits with improved thermal, mechanical, or anti-corrosion properties. Eor instance, it has been reported that colloidal cadmium sulfide [105] or mercuric sulfide [106] inclusions significanfly improve photoactivity and corrosion resistance of electrodeposited cadmium selenide. 

For instance, inaccurate positions of spherical hard-domains in their lattice of colloidal dimensions 2SIn real space there is a convolution of the ideal atom s position (a delta-function) with the real probability distribution to find it. 

Sol-gel process starts with a solution or a sol that becomes a gel. The solution can be prepared from either inorganic salts or organic components which than are hydrolyzed and condensed to make a sol or a gel. One can stop at the sol stage, which refers to a dispersion of particles of colloidal dimensions in a liquid, or proceed to the gel state which refers to a three-dimensionally-linked solid network with liquid filling the pores. These pores are interconnected in the wet gel state. 

The discrepancies encountered on attempting to interprete the physico-chemical properties of lignin are even more striking. For example, there are reported in the literature values for the molecular weight of lignin1 ranging from 250 to the colloidal dimensions of 12,000 (16). 

The IUPAC Commission on Macromolecular Nomenclature recommended micronetwork as a term for microgel [47] and defined it as a highly ramified macromolecule of colloidal dimensions. However, it should be noted that a micronetwork implies a structure and not a macromolecule or a particle, that a high ramification is not typical for these molecular particles and that the same wrong dimension is used as with microgel. 

Since microgels are intramolecularly crosslinked macromolecules of colloidal dimensions, it is necessary for their synthesis to control the size of the growing crosslinked molecules. This can be achieved by carrying out polymerization and crosslinking in a restricted volume, i.e. that of a micelle or of a polymer coil. Thus, two general methods of microgel synthesis are available (1) emulsion polymerization, and (2) solution polymerization. 

Finally, there are no gas-in-gas colloids we cannot suspend a gas within another gas, since it is not possible to have gas particles of colloidal dimensions. Introducing one gas to another generates a simple mixture, which follows the thermodynamics of mixtures, e.g. Dalton s law (p. 221). 

Most work on the surface of silica has been done with amorphous silica of colloidal dimensions. This is due to its large surface area and to its technical importance. We shall therefore discuss first the identification of surface groups on amorphous silica. 

Lyophilized copolymer was ground down to colloidal dimensions (<1 iJim) using a laboratory planetary mill (Pulverisette, Fritsch GmbH). A 110-mg sample of copolymer powder, 20 mg of bovine insulin, and 20 mg of GOD were mixed, and the mixture was compressed into a disk-shaped matrix of 5-mm thickness and 15-mm diameter. 

Gel in which the network component comprises particles of colloidal dimensions. 

The effect of slow accumulation of surface-active materials is indicated in Fig. 18, which is a series of photographs of drops suspended in a tapered tube (H9). Tiny amounts of fine solids of colloidal dimensions, as described by Elzinga and Banchero (El), gradually collected at the interface and were swept around to the rear of the drop. Circulation was progressively hindered until it was nearly stopped. Yet no measurable change could be detected in any physical property, including interfacial tension of the separated phases. 

The size of surfactant precipitate structures may vary widely, from colloidal precipitate, too small to be seen visually, to large crystals. This is an important property, because some deleterious effects of surfactant precipitation could be minimized or beneficial effects of precipitation could be negated if the precipitate were of colloidal dimensions. Examples of the importance of precipitate structure and size include the aforementioned oil field process and recovery of surfactant from surfactant-based separations via precipitation-fiItering. Effects of using surfactant mixtures on precipitate structures would be useful to know. 

The section on suspension polymerization indicated the differentiation between suspension and emulsion (or latex) polymerizations. Emulsion polymers usually are formed with the initiator in the aqueous phase, in the presence of surfactants, and with polymer particles of colloidal dimensions, i.e., on the order of 0.1 gm in diameter [17]. Generally, the molecular weights of the polymers produced by an emulsion process are substantially greater than those produced by bulk or suspension polymerizations. The rate of polymer production is also higher. As a large quantity of water is usually present, temperature control is often simple. 

One type of colloidal system has been chosen for discussion, a system in which the solid metal phase has been shrank in three dimensions to give small solid particles in Brownian motion in a solution. Such a colloidal suspension consisting of discrete, separate particles immersed in a continuous phase is known as a sol. One can also have a case where only two dimensions (e.g., the height z and breadth y of a cube) are shrank to colloidal dimensions. The result is long spaghettihke particles dispersed in solution—macromolecular solutions. 

Since the micelles are of colloidal dimensions, they are capable of scattering light and the white colour of milk is due largely to light scattering by the casein micelles the white colour is lost if the micelles are disrupted, e.g. by removing colloidal calcium phosphate (by citrate, ethylene... 

One can have the same type of situation in a blend of two mutually immiscible polymers (e.g., polymethylbutene [PMB], polyethylbutene [PEB]). When mixed, such homopolymers form coarse blends that are nonequilibrium structures (i.e., only kinetically stable, although the time scale for phase separation is extremely large). If we add the corresponding (PEB-PMB) diblock copolymer (i.e., a polymer that has a chain of PEB attached to a chain of PMB) to the mixture, we can produce a rich variety of microstructures of colloidal dimensions. Theoretical predictions show that cylindrical, lamellar, and bicontinuous microstructures can be achieved by manipulating the molecular architecture of block copolymer additives. 

Berg, H. C., Random Walks in Biology, expanded ed. Princeton University Press, Princeton, NJ, 1993. (Undergraduate level. A lucid introduction to random walk statistics. Discusses translational and rotational diffusion, self-propelled motion, random walk, and sedimentation Relevant to biological species of colloidal dimensions, but no background in biology is needed.)... 

Criticize or defend the following proposition The accompanying data for the turbidity of dodecylamine hydrochloride solutions suggest that at concentrations exceeding about 0.003 g cm 3 the solute associates into aggregates of colloidal dimensions. 

From what has been said, it will be seen that colloids may be prepared by methods which reduce the size of larger particles to colloidal dimensions or by starting with true solutions and bringing about the first step toward crystallization or precipitation. The methods employed are sometimes grouped in three classes ... 

Electrical dispersion sparking between electrodes under a solvent whereby the particles of the electrodes are torn off in colloidal dimensions. 

POWDER. Any solid, dry material of extremely small particle size ranging down to colloidal dimensions, prepared either by comminuting larger units (mechanical grinding), combustion (carbon black, lampblack), or precipitation via a chemical reaction (calcium carbonate, etc ). Powders that are so fine that the particles cannot be detected by rubbing between... 

The predominant oxidation stale of the element is (V). There is some evidence that the (IV) state is obtained under certain reduction conditions. When the pentapositive form is not in the form of a complex ion it may exist in solution as PaC>2+. The compounds are very readily hydrolyzed in aqueous solution yielding aggregates of colloidal dimensions, thus showing marked similarity to niobium and tantalum in this respect. These properties play a dominant role in the chemical properties of aqueous solution, because the element is so easily removed from solution by hydrolysis and adsorption Protactinium coprecipilates with a wide variety of substances, and it seems likely that the explanation for this lies in the hydrolytic and adsorptive behavior. 

SURFACE CHEMISTRY. This topic deals with the behavior of matter, where such behavior is determined largely by forces acting at surfaces. Since only condensed phases, i.e., liquids and solids, have surfaces, studies in surface chemistry require that at least one condensed phase be present in the system under consideration, The condensed phase may be of any size ranging from colloidal dimensions to a mass as large as an ocean. Interactions between solids, immiscible liquids, liquids and solids, gases and liquids, gases and solids, and different gases on a surface fall within the province of surface chemistry. 

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