Polydisperse systems applications

Another very important physical parameter one must consider is the size distribution of the colloids. A system consisting of particles of the same size is called a monodis-perse. A system with different sizes is called polydisperse. It is also obvious that systems with monodisperse will exhibit different properties from those of polydispersed systems. In many industrial application (such as coating on tapes used for recording music and coatings on CDs or DVDs), latter kind of quality of coatings is needed. 

In the past few decades, a specific kind of colloidal system based on monodis-perse size has been developed for various industrial applications. A variety of metal oxides and hydroxides and polymer lattices have been produced. Monodisperse systems are obviously preferred since their properties can be easily predicted. On the other hand, polydisperse systems will exhibit varying characteristics, depending on the degree of polydispersity. 

We believe that it would be useful not only to generalize the latest achievements in the rheology of extension of mono- and polydisperse systems, but also to assume and analyze some specific technological applications. Earlier works, which have become almost classical are referred to only for chronological accuracy and completeness of the view. 

In contrast to osmotic pressure, light-scattering measurements become easier as the particle size increases. For spherical particles the upper limit of applicability of the Debye equation is a particle diameter of c. A/20 (i.e. 20-25 nm for A0 600 nm or Awater 450 nm or a relative molecular mass of the order of 10 ). For asymmetric particles this upper limit is lower. However, by modification of the theory, much larger particles can also be studied by light scattering methods. For polydispersed systems a mass-average relative molecular mass is given. 

Ideally, it is desirable to solve equations 1 or 2 for the complete size distribution whenever polydisperse systems are being analysed. However, from the computational point of view, the direct application of the equations for monodisperse systems is more... 

K. Bunzl, Competitive ion exchange in mixed cation exchanger systems Kinetics and equilibria, J. Inorg. Nucl. Chem. 39 1049 (1977). See also K. Bunzl, Kinetics of ion exchange in polydisperse systems, Anal. Chem. 50 258 (1978) for an application to a set of exchangers with different specific surface areas. 

Application of these ideas to general polydisperse systems will require the extension of mean waiting time calculations to mixed structure matrices. 

As already indicated in Chapter 7, the introduction of laser technology has already had a major impact on light-scattering methods. These have found particular application in the development of new methods of particle sizing, and several instruments are now available commercially which arc designed for the automatic determination of particle size distributions. These methods are being developed steadily, especially in terms of the associated computer software needed for the rapid analysis of experimental data. In particular, while the measurement of the particle size in monodisperse systems is well established, the mathematical analysis for polydisperse systems and for non-spherical particles presents problems which are not yet fully solved. 

CH01 Choi, J.J. and Bae, Y.C., Liquid-liquid equilibria of polydisperse polymer systems Applicability of continuous thermodynamics, Fluid Phase Equil, 157, 213, 1999. 

The use of hexafluoroisopropanol (HFIP) as an SEC eluent has become popular for the analysis of polyesters and polyamides. Conventional PS/DVB-based SEC columns have been widely used for HFIP applications, although the relatively high polarity of HFIP has led to some practical difficulties (1) the SEC calibration curve can exhibit excessive curvature, (2) polydisperse samples can exhibit dislocations or shoulders on the peaks, and (3) low molecular weight resolution can be lost, causing additive/system peaks to coelute with the low molecular weight tail of the polymer distribution... 

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