Liquid, colloid systems

Emulsions are liquid-liquid colloidal systems. In other words, an emulsion may be defined as a dispersion of finely divided liquid droplets in another liquid. 

Fig. 3.7. Diagramatic representation showing the various ways a solid/liquid or liquid/liquid colloidal system may evolve [due to Vincent, B. (1984)]. Whatever the process used to fragment the macroscopic systems, a transition to the colloidal state consumes energy, of which a part remains stored within the system. This energy may be restituted by a more or less rapid change in the organisation of the matter, following one or more of the processes shown...

The incorporation of the filler into the polymer matrix is achieved by mixing of the aqueous dispersion of CNTs with the polymer particles, either by spraying of the CNTs on the surface of the "dry" polymer particles or by direct mixing of the two (liquid) colloidal systems made of the CNTs and the polymer particles, both stabilized by surfactants. In the first case, the powder obtained can directly be... 

Some liquid colloid systems show a double refraction when they are set in laminar flow. The classical example is the V2O5 sol which (at least after ageing) consists of needle-shaped particles with a crystalline character the sol itself with its particles randomly oriented by Brownian motion is isotropic if now one makes it flow through a tube or between two coaxial cylinders, one of which is rotating, it becomes double refracting The same is the case with many macromolecular sols This phenomenon, streaming double refraction of sols, is also reckoned as accidental double refraction, because it only occurs through a constraint exerted on the system ... 

By far the most important section of the province of stability theory relates to the production and destruction of liquid colloid systems These will be subject under discussion in subparagraph b, while in c the solid systems will be discussed ... 

Macromolecular substances above their melting point are of course to be considered as liquid colloid systems which, when the temperature faUs below the setting point, set and are then transformed into solid colloid systems This transition does not differ from that in other congealing substances of low molecular weight Reference can therefore be made to textbooks where such transitions are discussed ... 

A lot of natural as well as technological objects of analytical control are colloidal systems, i.e. human blood, biological liquids, sol and suspension forming in different technological processes (ore-dressing, electrochemical deposition, catalysis and other), food, paint-and-lacquer materials, sewage water and other. 

Solvation and especially hydration are rather complex phenomena and little is known about them. Depending on the kind of molecular groups, atoms or ions interacting with the solvent, one can differ between lyo- or hydrophilic and lyo-or hydrophobic solvation or hydration. Due to these interactions the so-called liquid structure is changed. Therefore it seems to be unavoidable to consider, at least very briefly, the intermolecular interactions and the main features of liquids, especially water structure before dealing with solvation/hydration and their effects on the formation of ordered structures in the colloidal systems mentioned above. 

Hoffman R (1975) A study of the advancing interface. I. Interface shape in liquid gas system. J Colloid Interface Sci 50 228-241... 

SO sharply defined that they are called surfaces. Well-defined surfaces occur between solids and either gases or liquids and thus are commonly found in catalytic and electrode reactions. More diffuse interfaces may occur between solids, as in microelectronic devices, and between fluids or semifluids, as in many polymeric and colloidal systems. 

While the nuclear magnetic resonance (NMR) technique has widely been used to study diffusion processes of normal liquids, solids, or colloidal systems, there are only a few applications to molten salts. The spin echo self-diffusion method with pulsed field gradients was applied to molten salts by Herdlicka et al. "" There is no need to set up or maintain a concentration gradient. 

Foams are agglomerations of gas bubbles separated from each other by thin films (5). Mainly, the problem is concerned with one class of colloidal systems —gas dispersed in liquid—but liquid dispersed in gas, solids dispersed in liquid (suspensions), and liquids dispersed in liquids (emulsions) cannot be ignored. The dispersion of a gas into a liquid must be studied and observed by the food technologist to improve the contact between the liquid and gas phases, the agitation of the liquid phase, and most important, the production of foam 10). 

In colloid science, colloidal systems are commonly classified as being lyophilic or lyophobic, based on the interaction between the dispersed phase and the dispersion medium. In lyophilic dispersions, there is a considerable affinity between the two constituent phases (e.g., hydrophilic polymers in water, polystyrene in benzene). The more restrictive terms hydrophilic and oleophilic can be used when the external phase is water and a nonpolar liquid, respectively. In contrast, in lyophobic systems there is little attraction between the two phases (e.g., aqueous dispersions of sulfur). If the dispersion medium is water, the term hydrophobic can be used. Resulting from the high affinity between the dispersed phase and the dispersion medium, lyophilic systems often form spontaneously and are considered as being thermodynamically stable. On the other hand, lyophobic systems generally do not form spontaneously and are intrinsically unstable. 

The interfacial properties of chain-like molecules in many polymeric and colloidal systems are dependent on the conformation of the chains adsorbed at the interface (.1). Chains adsorbed at the solid-liquid interface may be produced by anchoring diblock copolymers to particles in a polymer dispersion. Such dispersions are conveniently prepared by polymerizing in the presence of a preformed AB diblock copolymer a monomer dissolved in a diluent which is a precipitant for the polymer. The A block which is... 

Delmas et al. produced PVP-stabilized rhodium nanoparticles using the method reported by Hirai [32] to perform catalytic hydrogenation of oct-l-ene in a two-liquid-phase system [40]. These authors investigated the effect of various parameters on nanoparticle stability and activity under more or less severe conditions. It was also shown that PVP/Rh colloids could be reused twice or more, without any loss of activity. 

Not all colloid systems are stable. The most stable involve solid dispersion media, since movement through a solid host will be slow. Emulsions also tend to be stable think, for example, about a glass of milk, which is more likely to decompose than undergo the destructive process of phase separation. Aerosols are not very stable although a water-based polish generates a liquid-in-air colloid, the particles of liquid soon descend through the air to form a pool of liquid on the table top. Smoke and other solid-in-gas aerosols are never permanent owing to differences in density between air and the dispersed phase. 

Coacervation The separation of two liquid phases in colloidal systems. 

This latter case is the same result as Einstein calculated for the situation where slip occurred at the rigid particle-liquid interface. Cox15 has extended the analysis of drop shape and orientation to a wider range of conditions, but for typical colloidal systems the deformation remains small at shear rates normally accessible in the rheometer. The data shown in Figure 3.11 was calculated from Cox s analysis. His results have been confirmed by Torza et al.16 with optical measurements. The ratio of the viscous to interfacial tension forces, Rf, was given as ... 

Schultz, R. D., and Branson, L., The colloid rocket Progress towards a charged-liquid-colloid propulsion system, presented at Symp. Advan. Propulsion Concepts, 2nd, Boston, 1959. 

Sehuetze, W., and Mueller-Goymann, C.C., Mutual interactions between nonionie surfaetants and gelatin—investigations in eubie liquid crystalline systems and mieellar systems. Colloid Polym. Sci., 269 85-90 (1992). 

The study of the interfacial liquid-liquid phase however is complicated by several factors, of which the chief is the mutual solubility of the liquids. No two liquids are completely immiscible even in such extreme cases as water and mercury or water and petroleum the interfacial energy between two pure liquids will thus be affected by such inter-solution of the two homogeneous phases. In cases of complete intersolubility there is evidently no boundary interface and consequently no interfacial energy. On addition of a solute to one of the liquids a partition of the solute between all three phases, the two liquids and the interfacial phase, takes place. Thus we obtain an apparent interfacial concentration of the added solute. The most varied possibilities, such as positive or negative adsorption from both liquids or positive adsorption from one and negative adsorption from the other, are evidently open to us. In spite of the complexity of such systems it is necessary that information on such points should be available, since one of the most important colloidal systems, the emulsions, consisting of liquids dispersed in liquids, owe their properties and peculiarities to an extended interfacial phase of this character. 

The results of colloid science play a crucial role in our everyday lives From hair spray to shower gel, from the lacquer we are using to repaint our front doors to the LCD displays on our new computers, colloidal and liquid crystalline systems are omnipresent in our immediate surroundings. 

Porous inkjet papers are in general created from colloidal dispersions. The eventual random packing of the colloid particles in the coated and dried film creates an open porous structure. It is this open structure that gives photographic-quality inkjet paper its apparently dr/ quality as it comes off the printer. Both the pore structure and pore wettability control the liquid invasion of the coated layer and therefore the final destination of dyes. Dispersion and stability of the colloidal system may require dispersant chemistries specific to the particle and solution composition. In many colloidal systems particle-particle interactions lead to flocculation which in turn leads to an increase in viscosity of the system. The viscosity directly influences the coating process, through the inverse relation between viscosity and maximum coating speed. 

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