Dispersion, measurement filtration methods

Homola and Robertson (1975) have described a filtration method for determining the interaction between colloidal particles. This measures the minimum pressure required to initiate coagulation. It is therefore only applicable to dispersions of marginal stability, although it does represent a... 

Molecular Weight. Measurement of intrinsic viscosity in water is the most commonly used method to determine the molecular weight of poly(ethylene oxide) resins. However, there are several problems associated with these measurements (86,87). The dissolved polymer is susceptible to oxidative and shear degradation, which is accelerated by filtration or dialysis. If the solution is purified by centrifiigation, precipitation of the highest molecular weight polymers can occur and the presence of residual catalyst by-products, which remain as dispersed, insoluble soHds, further compHcates purification. 

Table 2.7 lists techniques used to characterise carbon-blacks. Analysis of CB in rubber vulcanisates requires recovery of CB by digestion of the matrix followed by filtration, or by nonoxidative pyrolysis. Dispersion of CB within rubber products is usually assessed by the Cabot dispersion test, or by means of TEM. Kruse [46] has reviewed rubber microscopy, including the determination of the microstructure of CB in rubber compounds and vulcanisates and their qualitative and quantitative determination. Analysis of free CB features measurements of (i) particulate and aggregate size (SEM, TEM, XRD, AFM, STM) (ii) total surface area according to the BET method (ISO 4652), iodine adsorption (ISO 1304) or cetyltrimethylammonium bromide (CTAB) adsorption (ASTM D 3765) and (iii) external surface area, according to the dibutylphthalate (DBP) test (ASTM D 2414). TGA is an excellent technique for the quantification of CB in rubbers. However, it is very limited in being able to distinguish the different types of... 

These are by far the most quantitative methods for the assessment of dispersing power. Known amounts of solids (in grams) with a surface area A (m g ) are equilibrated at a constant temperature with dispersant solutions of various concentrations, Cj. The bottles containing the various dispersions are rotated for several hours until equilibrium is reached, after which the particles are removed from the dispersant solution by centrifugation and/or filtration through Millipore filters. The dispersant concentration in the supernatant liquid, C2, is analytically determined by a suitable technique that can measure low concentrations. 

The method consists essentially of repetitive filtration of a series of dispersions through a filter bed at different constant pressures. The minimum coagulation pressure can be estimated from the number of latex particles retained in the bed (measured either gravimetrically or by an optical difference technique). This shows a sharp increase at the pressure corresponding to the onset of coagulation. 

Numerous factors militate against the widespread use of NMR microscopy the resolution is poor by optical standards, the apparatus is expensive, the technique requires a high level of scientific expertise and the arrangements for sample loading are inconvenient and restrictive. Set against these are the uniquely non-invasive character of the method, its sensitivity to fluid phases, its unique ability to measure specific molecular properties and the especially powerful insights it can provide regarding fluid dynamics. Studies in which NMR microscopy has been able to provide unrivalled information include those concerned with membrane filtration, flow and dispersion in porous media, non-Newtonian flow in viscoelastic fluids, nonequilibrium phase transitions, electrophoresis and... 

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