Colloidal gels

Enzymes Colloidal gels Up to 10 -10 faster Up to 10" -10 faster Ionic environment in solution Several-fold change... 

It is evident therefore that Fe salts dissolved in water produce highly acidic solutions and the simple, pale-violet, hexaaquo ion only predominates if further acid is added to give pH - 0. At somewhat higher values of pH the solution becomes yellow due to the appearance of the above hydrolysed species and if the pH is raised above 2-3, further condensation occurs, colloidal gels begin to form, and eventually a... 

Soft materials colloids, gels, and biomaterials, pp. 342-343 Phosphors and other luminescent materials, p. 647 Steel, p. 690... 

The colloidal particles can be crystalline or constitnte an amorphons agglomeration of individual molecnles. The definition also includes nonaggregated large macromolecules such as proteins. An arbitrary distinction is made between hydrophobic colloids (sols) and hydrophilic colloids (gels), which depends on the degree and type of interaction with the aqneons solvent. 

The gel point is defined as the point at which the entire solid mass becomes interconnected. The physical characteristics of the gel network depends upon the size of particles and extent of cross-linking prior to gelation. Acid-catalysis leads to a more polymeric form of gel with linear chains as intermediates. Base-catalysis yields colloidal gels where gelation occurs by cross-linking of the colloidal particles. 

Thixotropic. The ability of some colloidal gels to liquefy when subjected to shaking, vibration, or ultrasonic treatment and then to revert back to a gel or jelly-like form after time. 

Colloidal gel produced by the action of ultrasonically induced cavitation. 

The pore liquid is removed during drying (Step 5). Drying of colloidal gels (Method I) is relatively easy because the pores arc large (100 nm). Alkoxide-based gels have very small pores (1-10 nm). and thus large... 

Finally, in essentially noncrystalliiie materials, such as hydrous precipitates and colloidal gels, the water present is at Ihe limiting case of being a hydrate, in which virtually no bonding, in Ihe chemical sense, exists. 

A strain or stress sweep is used to establish the LVE region (Figure H3.2.4). The LVE region is a characteristic of a material. While the strain value at the limit of LVE rarely exceeds 0.1 for colloidal gels, a larger LVE region with a strain of up to 1 or more is usually observed for biopolymer gels (Clark and Ross-Murphy, 1987). 

Atrazine Organic colloids Gel chromatography Wijayaratne and Means (1984)... 

Microcrystalline cellulose (MCC) is obtained by a controlled acid treatment intended to destroy the molecular bonding in the amorphous zones of cellulose. Usually HC1 or H2SO4 are used at 110°C for 15 min over native cellulose or regenerated cellulose. Colloidal gels are thus obtained showing thixotropy. MCC is used in the preparation of pharmaceutical compressed tablets due to its binding and disintegration properties. 

The linear polyphosphates and cyclophosphates are hydrolysed extremely slowly at neutral pH and room temperature in comparison with other polyacids such as polyarsenates and polyvanadates, and are unique in this respect. The half-hydrolysis time for the P-O-P bonds in linear polyphosphates at pH 7 and 25 °C is several years (Van Wazer, 1958). The rate of hydrolysis of these bonds is increased by raising the temperature, reducing the pH, and by the presence in the solution of colloidal gels and complex cations. The hydrolysis of these bonds is dependent on the ionic strength of the solutions (Van Wazer, 1958). 

Gelatin is a light-colored translucent solid that is produced by boiling animal tissue, skin, and bones. It has a very low melting point, and forms a semisolid colloidal gel when mixed with water. Most gelatin is produced as a by-product of the meat and leather industries. Historically, gelatin has also been produced from the swim bladders of some fish (isinglass), and from anders (hartshorn jelly). 

The thermodynamic stability of the colloidal gel state has a perfectly natural explanation in terms of the coulombic attraction theory. Just as —> 0 as Xm —> 2a,... 

For these experiments, some of which were also conducted on the ILL D17 small-angle diffractometer, crystals of n-butylammonium vermiculite exhibiting the fewest obvious structural defects were selected and trimmed to a rectangular cross section with a razor blade. This enabled the surface area, and therefore the applied pressure, to be measured accurately. The samples were then immersed in a dilute solution of n-butylammonium chloride of the desired concentration and allowed to swell freely. After equilibration for at least two days at 7°C, the swollen (or colloidal) gel phase samples were placed into the uniaxial pressure cell shown in Figure 3.1. 

In the 1 to 2 pH range still other types of oxo species may be formed. At pH > 2 more condensed species and colloidal gels are formed leading to precipitation of the red brown gelatinous hydrous oxide. 

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