Selected Characterisation Techniques

As is evident in the many examples selected in this chapter to illustrate the molecular characterisation and analysis of polymer degradation and oxidation processes, almost, without exception, each study or investigation cited has involved use of more than one analytical method or characterisation technique, often many more than two. This clearly emphasises the importance of using a multi-technique approach to provide supportive, complementary and confirmatory information, since each technique or method yields a different aspect of the degradation/oxidation process in polymers. 

The last decade has seen the introduction of several new characterisation techniques which have been of major assistance in understanding the structure of monolayers at a molecular level. The most important of these has been the use of synchrotron radiation to obtain diffraction patterns from films at the air/water surface. In principle it would always have been possible to use X-rays for this purpose but the high intensity and highly monochromatic nature of the radiation from a synchrotron source has made this technique far easier to use. A selection of recent papers based on this technique is given [79-88], not all of which refer to simple fatty acids. The information available from such experiments is of two distinct kinds, though, in several studies, both kinds of information have been obtained. 

The novel large-pore vanadosilicates AM-13 and AM-14 (Aveiro-Manchester, structure number 13 and 14) containing stoichiometric amounts of vanadium (SiA = 10 and 4, respectively), have been synthesised. Characterisation techniques such as bulk chemical analysis (ICP), powder X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy, and N2, -hexane, benzene, tripropylamine and perfluorbutylamine adsorption measurements were used for the structural studies. The acid-base and redox properties of these materials were assessed by the conversion of isopropanol and ethanol oxidation, respectively. Both materials exhibit high selectivity to acetaldehyde indicating that these two novel vanadosilicates are promising redox catalysts. 

This chapter addresses the dispersion behaviour of colloidal suspensions as well as their stability. Since both terms are closely related to the particle size distribution they cannot be discussed without commenting on the employed characterisation techniques. Selected case studies illustrate the general considerations with a clear focus on p3Togenic powders. 

This brief review on the practice of dispersion monitoring— from scientific publications only— has mentioned several measurands and various characterisation techniques. It is very likely that they show different capabilities to reflect changes in size distribution and that these capabilities depend on the particle system involved. However, the scientific literature is rather sparse on studies that thoroughly examine the performance of characterisation teclmiques. There is no data basis for a general evaluation instead, selected examples with a focus on pyrogenic powders are presented below. 

The performance of porous ceramic membranes is typically expressed by the permeate flux (throughput) and the selectivity (separation ability), which in turn are governed by the pore size distribution, porosity and intrinsic membrane surface properties, and as such there are a variety of direct and indirect characterisation techniques used to evaluate the potential of a membrane and predict its performance. In this way new membranes can be efficiently and effectively screened and later optimised without the need for lengthy permeation experiments, reducing overall development time. Similarly, these techniques can be used to understand and/or verify a new membrane s transport and separation mechanisms. 

The physical characterisation of membrane structure is important if the correct membrane is to be selected for a given application. The pore structure of microfiltration membranes is relatively easy to characterise, SEM and AFM being the most convenient method and allowing three-dimensional structure of the membrane to be determined. Other techniques such as the bubble point, mercury intrusion or permeability methods use measurements of the permeability of membranes to fluids. Both the maximum pore size and the pore size distribution may be determined.1315 A parameter often quoted in manufacturer s literature is the nominal... 

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