Stable Colloidal Suspensions

It is operationally difficult to distinguish between dissolved and colloidally dispersed substances. For example, colloidal metal-ion precipitates occasionally have particle sizes smaller than 100 A, sufficiently small to pass through a membrane filter, and organic substances can exist as a stable colloidal suspension. Information on the types of species encountered under different chemical conditions (type of complexes, their stabilities, rate of formation) is a prerequisite to better understanding of the transformation in properties of toxic chemicals in a water body. 

Periodically, these mixtures were centrifuged and an aliquot of the clay-free supemate taken for counting analysis. Two naturally-occurring clays were selected for the experiments one was labeled kaolin (for the mineral kaolinite) while the second was referred to as attapulgite (or polygorshite). Both were obtained from the Source Clay Mineral Repository (3) as standard clays representative of each class of clay and were used as received. Stable, colloidal suspensions of each were prepared by ultrasonically dispersing weighed quantities of each clay in triple-distilled water. 

Phospholipids. The phospholipids comprise approximately 1 % of the total lipid in bovine milk (ca.0.3 to 0.4 g/liter). While quantitatively minor, the ability of the phospholipids to form stable colloidal suspensions or emulsions in aqueous solution cause them to be important in the formation and secretion of milk fat. (Long and Patton 1978 Patton and Keenan 1975). Their physical properties as bipolar molecules and their relatively high concentration of unsaturated fatty acids also make them an important factor to consider during the storage and... 

The precursor in a sol-gel preparation can either be a metal salt/alkoxidc dissolved in an appropriate solvent or a stable colloidal suspension of preformed sols. Metal alkoxidcs have been the most extensively used because they are commercially available in high purity and their solution chemistry has been documented [1-3]. At its simplest level, sol gel chemistry... 

Bazzi et al. (2003, 2004) reported (Figure 19) the colloidal precipitation from polyalcohol solution to obtain stable colloidal suspensions of luminescent doped rare earth oxide nanocrystals with an average grain... 

Experimental. Samples for electrophoretic mobility (EM) measurements were prepared as previously described for the titration experiments except that violent mixing with destruction of carbon agglomerates was desirable here and was promoted with a 5-10 minute treatment of the capped serum bottles in an ultrasonic bath. The indicator was, of course, deleted in the EM sample preparation procedure. Following mixing, a few drops of the mixture was transferred to a 25 ml flask of benzene and given another ultrasonic treatment. This procedure produced a fairly stable colloid suspension of the carbon black which was used to fill the glass-Teflon commercially available EM cell manufactured by Zeta-Meter, Inc. 

Dispersants/detergents. The action of dispersants has been described elsewhere (Section 14.2.1 and 14.2.2). Their purpose is to impart an electrical charge to particulate matter (formed as a result of chemical reactions or already present in the process stream), so that it becomes a stable colloidal suspension thereby preventing agglomeration and potential deposition. Stephenson and Rowe [1993]... 

In microelectrophoresis the particle velocity is observed directly with a microscope (or ultramicroscope). It is applicable to reasonably stable colloidal suspensions or emulsions containing microscopically visible particles or droplets in sufficiently dilute concentration that the individual particles can be distinguished. The electrophoretic behavior is then measured directly. 

The present review focuses on gels, as supported metallic catalyst precursors or catalyst support precursors, obtained from a homogeneous solution of monomer precursors. Gels obtained from the destabilization of a stable colloidal suspension, while representing an important class of sol-gel materials, are not presented here. 

As two particles approach one another in the liquid, the diffuse double layers will start to overlap. It is the interaction between the double layers that gives rise to the repulsion between the particles. If the repulsion is strong enough, it can overcome the van der Waals attractive force, thereby producing a stable colloidal suspension. As a prelude to examining the interactions between double layers, we start with an isolated double layer associated with a single particle. 

The particulate gel route is not effective for the production of dense ceramics from crystalline particles because the large pore size relative to the particle size is thermodynamically unfavorable for achieving densification in crystalline systems (see Chapter 9). The trend in the production of crystalline ceramics, as we have indicated earlier, is towards the use of fine particles that are consolidated uniformly from stable colloidal suspensions (Fig. 5.2). 

The polymers used as surfactants can be synthetic or natural molecules able to yield stable colloidal suspensions designed for drug delivery. Nevertheless, synthetic polymers have the advantage of high purity and reproducibility over natural polymers. 

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