Mechanism and Other Methods

Some of the difficulties for M or PSD determination may be solved using other types of chromatogra-phy: liquid, FFF - normal and steric (SFFF) - supercritical fluid, capillary electrophoresis, or combining with other methods (thermal FFF). Countercurrent chromatography or centrifugal partition chromatog-raphy is a potential tool for separating copolymers of different structure or nature, but currently there are few examples. These methods correspond to a large variety of separation mechanisms based on kinetics or thermodynamics, where surface, volume, active specific sites of materials and thermal, gravity, electric, magnetic applied fields bring their contribution. They are also called fractionation and have features in common with chromatography. One characteristic is the absence of the stationary phase, which avoids the problems of interfering phenomena such as adsorption, mass transport, column channelling, degradation and shear rate. This allows a greater choice of eluent.

Some other solutions are nonchromatographic methods, working with or without separation, such

Table 3 Comparison between capillary and packed columns for HDC

Column Length Diameter V u Shear AP N N H RF max Range

Type (m) (mm) (mL) (cms-1) (s-) (bar) (m) (cm) (mm)

Capillary 120 0.25 5.9 34 10~4 175 1500 12.5 8 1.45 0.8-20

packed 0.5 5 7.4 0.1 10~8 35 7000 14000 0.007 1.15 0.05-1

Reproduced with permission from Revillon etal. (1991) Journal of Applied Polymer Science: Applied Polymer Symposium 48: 243-257.

as dynamic light scattering (photocorrelation spectroscopy) and sedimentometry under centrifugation in a disc. In the presence of SDS, at low ionic strength, HDC results in the range of 200 nm are slightly higher but close to disc centrifuge values. The latter method is of high resolution, since the separation time is inversely proportional to the diameter squared. Analysis time is low in photocorrelation spectroscopy (1min) and is similar for HDC and centrifugation in a disc. Photocorrelation spectros-copy operated with a proper choice of parameters, gives an excellent correlation with transmission electron microscopy values and an excellent resolution for the mixture of two latexes.

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