There is no limitation to the nature of the sample, but most studies are in the polymer field. In control and in research, particle characterization is a necessity and numerous chemical and physical data have to be determined, such as molecular weight distribution (MWD) and averages (M) or PSD. These values are key parameters for determining rheological, mechanical, thermal and optical properties, storage stability, film-forming capability and the general behaviour of polymer materials. MWD and M are commonly measured by SEC and particle size may be obtained by a variety of methods.

To reduce use of organic solvents in the production of polymers (by bulk and in organic solvent processes), free radical suspension and emulsion polymerization heterogeneous processes are used. The first process leads to larger bead sizes (around mm), which are not dealt with in HDC but HDC is typically suited for latex evaluation (around 100 nm) obtained by the second process. These polymer particles are used either largely in water-borne paints, inks and relatively low cost coatings, or as high value colloids for model compounds. For instance, they are used as standards for calibration (membranes) or in biochemistry for diagnostic aids and purification, or for packing chromatography columns. Much of the practical HDC work has been devoted to synthetic organic colloid separation and diameter measurements for quality control. Separation of natural products such as proteins is also of interest. The rapidity of the measurement is compatible with kinetic studies and monitoring during the polymerization process. Swelling of carboxylic latexes has been measured according to pH. The stability of mini-emulsions (50-500 nm) has been studied successfully. Floccula-tion of colloids in the presence of water-soluble ionic polymers or inorganic oxides has been observed by HDC in conjunction with other methods. Association of particulates under the effect of a thickener is clearly demonstrated, though it can be broken by intensive shear, and the same applies to aggregates.

Some authors have attempted to determine molecular weight or size for very large polymers, for instance water-soluble ones, like polyacrylamide, xanthane, polysaccharides and tobacco mosaic virus. The flow and dynamic behaviour of macromolecules in packed bed have been studied.

A variety of other compounds have been examined, such as carbon black, paper fibres, cement, clay, metals and oxides of Fe, Ti, Si, Al, silver halides and biomaterials such as milk or liposomes from egg yolk lecithin. Silica has been extensively used since it has the advantage of being a hard spherical model for HDC mechanism studies.

Moreover, HDC is of interest in the fundamental study of flow behaviour in tubing or pores which are encountered in transport technology of materials. Applications are also found in geology.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment