Colloidal material definition

Comparison of model fit variances for cerium indicates a definite superiority of the DFO model over single-site sorption models. The large data scatter in groundwater cerium concentrations, and the ambiguity in extraction inventory trends, indicate that systems producing significant colloidal material may require more specialized models and experimental methods to fully understand their transport mechanisms ... 

Ralph K. Iler devoted MOST OF his career to exploratory and industrial research in the chemistry of colloidal materials. He is recognized worldwide for his unique contributions to a unified understanding of the colloidal chemistry of silica and silicates. His book The Chemistry of Silica, published in 1979, is the definitive book on silica chemistry and remains a primary source of reference in the field. 

However, amongst the chemical foundations on which the pioneers of supramolecular chemistry were building, although sometimes without acknowledgment, were the basic principles of colloid science. Colloid chemistry had been long established by the time of the initial development of supramolecular chemistry, and had also focused on the behavior of ensembles of molecules—typically mediated through noncovalent interactions. Indeed, the concept of self-assembly is fundamental in the study and manipulation of colloidal materials. By definition, colloids consist of a dispersed phase (or discontinuous phase) distributed... 

The subject of this chapter represents one of the most diverse areas in soft matter science. Colloidal materials are systems in which small droplets or particles of one material are dispersed in a continuous phase of another material. This definition is deliberately broad as colloidal systems span an extremely wide range of materials, from solid particles suspended in aqueous solution, to droplets of moisture in the air, and foams, and can even be extended to include granular materials like sand. Colloidal science is a subject that is particularly relevant in our everyday lives because it plays an important role in the manufacture of numerous everyday substances. Many of the foods we eat can be described as colloids. Creamy foods, like mayonnaise, sauces, or ice cream, contain tiny droplets of fat dispersed in an aqueous medium food can be foams (liked whipped cream), and it can be a solid sponge (like bread or cake). Personal care products like face creams and toothpastes are colloidal systems, as are household paints and inks. Even the dilute polymer solutions discussed in Chapter 4 can be considered colloids. 

The retained components, the ones to which the medium is impermeable, may be particles of solid, droplets of liquid, colloidal material, or molecular or ionic species in solution, while the permeate (or filtrate) will normally be the suspending fluid or solvent, possibly together with some of the other components. (Note this definition includes the diffusion processes of reverse osmosis and nanofiltration, which are not strictly filtration processes, because of their similarity to membrane ultrafiltration and microfiltration, which are.)... 

For tire purjDoses of tliis review, a nanocrystal is defined as a crystalline solid, witli feature sizes less tlian 50 nm, recovered as a purified powder from a chemical syntliesis and subsequently dissolved as isolated particles in an appropriate solvent. In many ways, tliis definition shares many features witli tliat of colloids , defined broadly as a particle tliat has some linear dimension between 1 and 1000 nm [1] tire study of nanocrystals may be drought of as a new kind of colloid science [2]. Much of die early work on colloidal metal and semiconductor particles stemmed from die photophysics and applications to electrochemistry. (See, for example, die excellent review by Henglein [3].) However, the definition of a colloid does not include any specification of die internal stmcture of die particle. Therein lies die cmcial distinction in nanocrystals, die interior crystalline stmcture is of overwhelming importance. Nanocrystals must tmly be little solids (figure C2.17.1), widi internal stmctures equivalent (or nearly equivalent) to drat of bulk materials. This is a necessary condition if size-dependent studies of nanometre-sized objects are to offer any insight into die behaviour of bulk solids. 

Increasingly chemists are contributing to the synthesis of advanced materials with enhanced or novel properties by using colloidal assemblies as templates. Colloid chemistry is particularly well suited to this objective since nanoparticles, by definition, are colloidal and since processing of advanced materials involve reactions at solid-solid, solid-liquid or solid-gas interfaces (3-5). 

The van der Waals forces scale up from atomic distances to colloidal distances undiminished. How the molecular forces scale up in the case of large objects, expressions for such forces, definition of the Hamaker constant, and theories based on bulk material properties follow in Sections 10.5-10.7. 

BENTONITE. The term applied to alteied fine-grained volcanic ashes which have been blown considerable distance from their origin and deposited m marine waters. The resulting material is usually a white, but sometimes a colored, clay-like sediment which may contain bits of volcanic glass but is composed mainly of colloidal silica which will absorb large quantities of water. Since bentonites are wind-blown deposits they are useful as definite datum planes in stratigraphy, especially in helping to determine the contemporaneity of the different facies of marine sediments. 

Emulsions are colloidal dispersions of liquid droplets in another liquid phase, sometimes stabilized by surface active agents. Emulsions thus consist of a discontinuous phase, dispersed in a continuous phase. The most common types of emulsions are water-in-oil (W/O) in which oil is the continuous phase, and oil-in-water (OAV) in which water forms the continuous phase. However, this traditional definition of an emulsion is too narrow to include most food emulsions. For example, in foods the dispersed phase may be partially solidified, as in dairy products or the continuous phase may contain crystalline material, as in ice cream. It may also be a gel, as in several desserts. In addition to this, air bubbles may have been incorporated to produce the desired texture. 

The concise scientific definition of an aerosol refers specifically to a colloidal state of material suspended in a gas. However, the term has acquired an additional meaning in common household usage. In the commercial packaging field, the term aerosol now is synonymous with pressurized products that are released in a dispersed form from a can or a bottle. The discharge ranges from coarse fogs and mists to finely divided liquid or powder dispersions. 

Prior to discussing the factors that control concentrations of the major dissolved components in rivers, estuaries, and oceans, it is important to discuss the operationally defined size spectrum for different phases (dissolved, colloidal, and particulate) of an element. The conventional definition for dissolved materials is the fraction of total material that... 

Silica is one of the most abundant chemical substances on earth. It can be both crystalline or amorphous. The crystalline forms of silica are quartz, cristobalite, and tridymite [51,52]. The amorphous forms, which are normally porous [149] are precipitated silica, silica gel, colloidal silica sols, and pyrogenic silica [150-156], According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), porous materials can be classified as follows microporous materials are those with pore diameters from 3 to 20 A mesoporous materials are those that have pore diameters between 20 and 500 A and macroporous materials are those with pores bigger than 500 A [149],... 

SOLUBILITY OF PRECIPITATES A large number of reactions employed in qualitative inorganic analysis involve the formation of precipitates. A precipitate is a substance which separates as a solid phase out of the solution. The precipitate may be crystalline or colloidal, and can be removed from the solution by filtration or by centrifuging. A precipitate is formed if the solution becomes oversaturated with the particular substance. The solubility (5) of a precipitate is by definition equal to the molar concentration of the saturated solution. Solubility depends on various circumstances, like temperature, pressure, concentration of other materials in the solution, and on the composition of the solvent. 

Caoutchouc so obtained is a colorless, transparent hydrocarbon of the composition CsHg or better (CsHg) . It is an emulsion colloid of a density approximately 0.90. It is a non-conductor of electricity and this is one of its important properties. It takes up liquids and swells. It is moderately resistant to the diffusion of gases and can be used for balloons but is not as good as other materials. Pure caoutchouc is a soft, sticky, gummy mass of low elasticity and in this condition possesses almost no desirable technical properties. In order to give it such properties it is very definitely changed in the process of manufacture. 

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