Colloidal state

As it is now possible by choice of suitable conditions to prepare most compounds in this form, the colloid state should be considered as a physical state in which all substances can be made to exist. Many ma terials such as proteins, vegetable fibres, rubber, etc. are most stable or occur naturally in the colloidal slate. In the colloidal stale the properties of surface are all-important. 

Collimation Collimators (+)-CoUinusin S. collinus Tb 365 Colloidal particles Colloidal silica Colloidal silver Colloidal state Colloidal sulfur Colloid mills Colloids... 

Dispersants (qv) have been added to the pulper to maintain stickies in a colloidal state. The small particle size reduces the problems stickies cause on the paper machine and in paper products. Among the chemicals that have been used are fatty alcohol ethoxylates, alkylphenol ethoxylates, lignosulfonates, and naphthalene sulfonates (18). 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

Many attempts have been made to characterize the stabiUty of the colloidal state of asphalt at ordinary temperature on the basis of chemical analysis in generic groups. For example, a colloidal instabiUty index has been defined as the ratio of the sum of the amounts in asphaltenes and flocculants (saturated oils) to the sum of the amounts in peptizers (resins) and solvents (aromatic oils) (66) ... 

The weathering process which eventually reduces the rock of the parent material to the inorganic constituents of soil comprises both physical and chemical changes. Size reduction from rocks to the colloidal state depends not only upon the mechanical action of natural forces but also on chemical solubilisation of certain minerals, action of plant roots, and the effects of organic substances formed by biological activity. 

Problems which arise with certain precipitates include the coagulation or flocculation of a colloidal dispersion of a finely divided solid to permit its filtration and to prevent its re-peptisation upon washing the precipitate. It is therefore desirable to understand the basic principles of the colloid chemistry of precipitates, for which an appropriate textbook should be consulted (see the Bibliography, Section 11.80). However, some aspects of the colloidal state relevant to quantitative analysis are indicated below. 

The colloidal state of matter is distinguished by a certain range of particle size, as a consequence of which certain characteristic properties become apparent. 

An important consequence of the smallness of the size of colloidal particles is that the ratio of surface area to weight is extremely large. Phenomena, such as adsorption, which depend upon the size of the surface will therefore play an important part with substances in the colloidal state. 

Cobalt, sepn. of from nickel, (cm) 532 Codeine and morphine, D. of 740 Coefficient of variation 135 Colloidal state 418 See also Lyophilic, Lyophobic Colorimeters light filters for, 661 photoelectric, 645, 666 Colorimetric analysis 645 criteria for, 672 general remarks on, 645, 672 procedure, 675 solvent selection, 674 titration, 652... 

This paper reviews the experiences of the oil industry in regard to asphaltene flocculation and presents justifications and a descriptive account for the development of two different models for this phenomenon. In one of the models we consider the asphaltenes to be dissolved in the oil in a true liquid state and dwell upon statistical thermodynamic techniques of multicomponent mixtures to predict their phase behavior. In the other model we consider asphaltenes to exist in oil in a colloidal state, as minute suspended particles, and utilize colloidal science techniques to predict their phase behavior. Experimental work over the last 40 years suggests that asphaltenes possess a wide molecular weight distribution and they may exist in both colloidal and dissolved states in the crude oil. 

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. 

Many chemical changes occurring in living processes are catalyzed by enzymes which are complex protein substances produced by living cells. Enzymes are often present in colloidal state and are very specific in their catalytic action. Zymase obtained from yeast catalyses the fermentation of dextrose but is ineffective in breakdown of cane sugar. 

Graham s definitions were expanded, and the concept of a colloidal state of matter evolved. According to this view, a substance could occur in a colloidal state just as it could occur under various conditions as a gas, liquid, or solid. If a colloidal solution was, at that time, defined as a solution in which the dispersed particles were comprised of large molecules, the ascertion would have been more acceptable. 

In support of the association theory, colloid chemists cited non-reproduceable cryoscopic molecular weight determinations (which were eventually shown to be caused by errors in technique) and claimed that the ordinary laws of chemistry were not applicable to matter in the colloid state. The latter claim was based, not completely without merit, on the ascerta-tion that the colloid particles are large aggregates of molecules, and thus not accessible to chemical reactants. After all many natural colloids were shown to form double electrical layers and adsorb ions, thus they were "autoregulative" by action of their "surface field" (29). Furthermore, colloidal solutions were known to have abnormally high solution viscosities and abnormally low osmotic pressures. 

The essential differences between the properties of matter when in bulk and in the colloidal state were first described by Thomas Graham. The study of colloid chemistry involves a consideration of the form and behaviour of a new phase, the interfacial phase, possessiug unique properties. In many systems reactions both physical and chemical are observed which may be attributed to both bulk and interfacial phases. Thus for a proper understanding of colloidal behaviour a knowledge of the properties of surfaces and reactions at interfaces is evidently desirable. 

Saucier, C. et al., Characterization of (+)-catechin-acetaldehyde polymers a model for colloidal state of wine polyphenols. J. Agric. Food Chem. 45, 1045, 1997. 

Sols and Gels. The essence of the behavior characteristic of the colloidal state is that double-layer interactions are as significant as bulk interactions. In other words, surface interactions are on a par with volume interactions. This condition can therefore be realized in all systems where the surface-to-volume ratios are high, i.e., at submicroscopic dimensions. 

Materials in a colloidal state are frequently preferred in industrial processing operations because their large surface areas per unit volume enhance chemical reactivity, adsorptive capacity, heat transfer rates, and so on. Therefore, one cannot overlook the importance of the flow behavior and properties of colloids since they exert a significant influence on the performance, efficiency, and economy of the process. Note that some examples of this (e.g., ceramic processing, electrophoretic display devices, and food colloids) were mentioned in the vignettes presented in Chapter 1. In addition, one often uses the flow properties and behavior of the products as measures of the microstructure (or, morphology ) of the products and as a means of quality control (e.g., printing inks, toners, paints, skin creams, blood substitutes,... 

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