Colloidal systems types

As in previous theoretical studies of the bulk dispersions of hard spheres we observe in Fig. 1(a) that the PMF exhibits oscillations that develop with increasing solvent density. The phase of the oscillations shifts to smaller intercolloidal separations with augmenting solvent density. Depletion-type attraction is observed close to the contact of two colloids. The structural barrier in the PMF for solvent-separated colloids, at the solvent densities in question, is not at cr /2 but at a larger distance between colloids. These general trends are well known in the theory of colloidal systems and do not require additional comments. 

Figure 6.2. (a). Colloidal silica network on the surface of spores from Isoetes pantii (quill wort). Scale = 20 pm. (b). Polystyrene networks and foams produced as a biproduct of colloidal latex formation. Both types of colloidal system are typical of the diversity of patterns that can be derived from the interactions of minute particles. Scale (in (a)) = 50pm. 

There are other approximations in the literature that may be more appropriate for particular conditions.12,27,29,35 In many colloidal systems the value of <5 is 2 nm < <5 < 10 nm and until h < 2S the pair potential will be dominated by the other types of interparticle interactions, i.e. it is of short range, albeit very steep. 

To sum up, the choice of operating conditions for a specific FFF application is made in a way that recalls the general criteria used in chromatography. An accurate search of literature addressed to similar samples that have been already analyzed by FFF techniques is very useful. A number of specific reviews have been published concerning, for example, enviromnental, pharmaceutical, and biological samples (see Section 12.5). As previously mentioned above, one of the most important factors is the stability of the considered colloidal system, for which a great deal of information can be obtained from specialized literature, such as colloid, polymer, and latex handbooks [33], For example, the use of the proper surfactant (e.g., Fl-70) is common for SdFFF applications. Polymer analysis with ThFFF requires solvent types similar to those employed in size exclusion chromatography. 

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. 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

The colloidal structures described above are dictated by thermodynamics, and the resulting structures are thermodynamically stable. Similar thermodynamically stable structures can develop even in a copolymer melt (i.e., there is no other polymer or solvent). Such colloidal systems differ from kinetically stable lyophobic dispersions of the type discussed in Vignettes 1.4 and 1.5. 

Accordingly, in the earlier exercises, 23 in number, attention is centered on methods of manipulation for overcoming the usual varieties of difficulties and in gaining experience in the use of preparative processes. Later exercises are arranged with reference to a number of types of compounds and the reactions available for their preparation. A final group of exercises is provided to illustrate the chief characteristics of colloidal systems. 

The entire picture is still more confusing because of the fact that several different types of colloids are distinguished—i.e., radiocolloids, pseudo-colloids (7, 8, 28, 33), and true colloids. Radio-colloids refer to systems of radiotracers which appear to be in colloidal form although they are in concentrations well below their ionic solubility (25, 26). The term pseudo-colloid is used to describe the formation of a colloid system... 

Micellar systems (i.e.,. Shenoy 1984 Ohlendorf Brunn) as well as other colloidal systems (polyphosphates (Hunston), tri-n-butyl-tin-fluoride, e.g. Dunn Evans) come under the heading surfactants . It is necessary to differentiate soaps into anionic, cationic, and non-ionic types. Among the anionic types one can find, for instance, alkali metals and ammonium salts consisting of various fatty acids, which were... 

SOAPS. Chemically, a soap is defined as any salt of a fatly acid containing 8 or more carbon atoms. Structurally a soap consists of a hydrophilic (water compatible) carboxylic add which is attached to a hydrophobic (water repellent) hydrocarbon. Soap molecules thus combine two types of behavior in one structure part of the molecule is attracted to water and the other part is attracted to oil. This feature underlies the function of these materials as surface active agents, or surfactants. Soaps are one class of surfactants. The other classes generally are called detergents. See also Colloid Systems and Detergents. 

Set up a circus of gels, sols, emulsions and foams, e.g. jelly , milk, pumice stone, polyurethane foam, bread, emulsion paint, cola, hair cream, aerosol dispenser, salad cream. A silica gel can be made from sodium silicate and hydrochloric acid. Classify the examples according to type of colloidal system. 

Emulsions and suspensions are colloidal dispersions of two or more immiscible phases in which one phase (disperse or internal phase) is dispersed as droplets or particles into another phase (continuous or dispersant phase). Therefore, various types of colloidal systems can be obtained. For example, oil/water and water /oil single emulsions can be prepared, as well as so-called multiple emulsions, which involve the preliminary emulsification of two phases (e.g., w/o or o/w), followed by secondary emulsification into a third phase leading to a three-phase mixture, such as w/o/w or o/w/o. Suspensions where a solid phase is dispersed into a liquid phase can also be obtained. In this case, solid particles can be (i) microspheres, for example, spherical particles composed of various natural and synthetic materials with diameters in the micrometer range solid lipid microspheres, albumin microspheres, polymer microspheres and (ii) capsules, for example, small, coated particles loaded with a solid, a liquid, a solid-liquid dispersion or solid-gas dispersion. Aerosols, where the internal phase is constituted by a solid or a liquid phase dispersed in air as a continuous phase, represent another type of colloidal system. 

The potential in the diffuse layer decreases exponentially with the distance to zero (from the Stem plane). The potential changes are affected by the characteristics of the diffuse layer and particularly by the type and number of ions in the bulk solution. In many systems, the electrical double layer originates from the adsorption of potential-determining ions such as surface-active ions. The addition of an inert electrolyte decreases the thickness of the electrical double layer (i.e., compressing the double layer) and thus the potential decays to zero in a short distance. As the surface potential remains constant upon addition of an inert electrolyte, the zeta potential decreases. When two similarly charged particles approach each other, the two particles are repelled due to their electrostatic interactions. The increase in the electrolyte concentration in a bulk solution helps to lower this repulsive interaction. This principle is widely used to destabilize many colloidal systems. 

Our consideration can easily be extended on a variety of colloidal systems. For example, the behavior of a charged particle near a (charged) wall can be described in a similar way, only with a DLYO-like potential instead of a Coulombic-type pair potential used throughout the paper (see [32], for example). 

The second type of potentiometric titration curves are shown in Figures 3.36b and c. Figure 3.36b shows that the crossover point of the same colloid system as in Figure... 

Polymers in colloidal systems function in a variety of ways depending on their molecular structure and concentration, the nature of the solvent, and the characteristics of the particles. Three primary types of situations exist for homopolymers. ... 

Several methods have been developed for preparing nanoparticles and are optimized on the basis of their physicochemical properties (e.g., size and hy-drophilicity) with regard to their in vivo fate after parenteral administration. The selection of the appropriate method for preparing drug-loaded nanoparticles depends on the physicochemical properties of the polymer and the drug. On the other hand, the procedure and the formulation conditions will determine the inner structure of these polymeric colloidal systems. Two types of systems with different inner structures are possible ... 

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