Conducting polymers characterisation

A generalised structure of an electronic nose is shown in Fig. 15.9. The sensor array may be QMB, conducting polymer, MOS or MS-based sensors. The data generated by each sensor are processed by a pattern-recognition algorithm and the results are then analysed. The ability to characterise complex mixtures without the need to identify and quantify individual components is one of the main advantages of such an approach. The pattern-recognition methods maybe divided into non-supervised (e.g. principal component analysis, PCA) and supervised (artificial neural network, ANN) methods also a combination of both can be used. 

There is an enormous body of work on quasielastic neutron scattering from polymers [1,2]. There is a smaller literature on neutron vibrational spectroscopy of polymers but this has had a significant impact on the characterisation of these materials. Crystalline or semi-crystalline polymers are the most important class of polymers commercially. The most-studied and technologically most important of these is polyethylene and this will be considered in some depth and we will highlight the use of the n-alkanes as model compounds ( 10.1.2). We will then see how these concepts can be transferred to polypropylene ( 10.1.3), nylon ( 10.1.4), and conducting polymers ( 10.1.5). Non-crystalline polymers ( 10.2) have been much-less studied by INS. As examples, we will consider polydimethylsiloxane ( 10.2.1) and advanced composites ( 10.2.2). 

FIGURE 6.9 Illustration of chain structure of poly(3-alkylthiophene) showing effect of head-head (HH) coupling in a mainly head-tail (HT) coupled chain. (From Jeffries-El, M. and McCullough, R.D., in Handbook of Conducting Polymers. Conjugated Polymers. Theory, Synthesis, Properties and Characterisation, 3rd edition, Skotheim, T.A. and Reynolds, J.R. (Eds.), CRC Press, Boca Raton, 2007, 9-1. With permission.)... 

Stella, R., Barisci, J.N., Serra, G., Wallace, G.G., and De Rossi, D. Characterisation of olive oil by an electronic nose based on conducting polymer sensors. Sensors and Actuators B Chemical, 63,1-9. 2000. 

J.N. Barisci, R. Stella, G.M. Spinks, and G.G. Wallace, Characterisation of the topography and surface potential of electrodeposited conducting polymer films using atomic force and electric force microscopies. Electrochim. Acta, 46, 519 (2000). 

Figure 9.18 Topography image (left), and SP image (right), of a PPy/p-toluene sulphonate (PTS) film grown potentiostatically at 0.6 V for 5 min, thickness 150 nm. (Reprinted with permission from Electrochimica Acta, Characterisation of the topography and surface potential of electrodeposited conducting polymer films using atomic force and electric force microscopies by J. N. Barisci, R. Stella, G. M. Spinks and G. G. Wallace, 46, 4. Copyright (2000) Elsevier Ltd)...

Like all types of polymers, conductive polymers are first characterised by spectroscopic techniques, and this is of particular importance for nanostructured materials too. Atomic force microscopy (AFM) is a powerful (and relatively inexpensive) microscopic technique for surface studies at nanoscale, and sometimes this is essential for the investigation of conductive polymers. Despite available limitations, progress in nanodevices has provided... 

The development of nanostructured conductive polymers also requires the development of advanced characterisation techniques, and this aspect of current research is captured in several chapters. A detailed review of Atomic Force Microscopy (AFM) covers the wide range of related scanning probe microscopes that are particularly relevant to soft materials. It also shows how techniques such as conductive AFM go beyond structural measurements to image the functional properties of materials relevant to applications such as solar cells. A wide range of spectroscopic techniques has also been reviewed, showing how they can be applied to learn about the interactions between conductive polymers and nanostructured... 

King, G. and S.J. Hi ns. 1995. Synthesis and characterisation of novel substituted benzo[c] thiophenes and polybenzo[c]thiophenes Tuning the potentials for n- and p-doping in transparent conducting polymers. / Mater Chem 5 447. 

Malitesta, C., Morea, G. et al. (1993). X-Ray photoelectron spectroscopy analysis of conducting polymers. Surface Characterisation of Advanced Polymers. L. Sab-batini and P. G. Zambonin. Weinheim, VCH. 

Misoska, V. Price, W. E. Ralph, S. R Wallace, G. G. Ogata, N. Synthesis, characterisation and ion transport studies on polypyrrole/deoxyribonucleic acid conducting polymer membranes. Synth. Met. 2001,123, 279-286. 

Williams el al. [421] have assessed the potential of UVRRS as a general analytical tool, both to distinguish between molecules with similar electronic absorptions, and to wavelength tune the laser to enhance selectively the Raman spectrum of individual components in a complex mixture. Raman spectroscopy provides a method whereby the distribution of polyene sequence lengths can be monitored. Not surprisingly, resonance Raman is also a major tool for characterising conducting polymers [422]. 

The intention in this chapter is to provide the reader with a balanced picture of the complementary roles of Raman and infrared spectroscopy in polymer characterisation. The emphasis chosen is towards practical applications, particularly those of significant industrial or analytical relevance. An attempt has been made to target as wide a range as possible, and to give examples of the many chemical and physical characterisations regularly undertaken. In doing this the intention is to provide as well exampled and referenced a text as could reasonably be accommodated, and to have provided those interested in more detail with a short route to important texts. Unfortunately, space constraints have inevitably necessitated the omission of certain important classes of materials such as biomolecules and conducting polymers. 

DETA (dielectric thermal analysis) Electrical equivalent of DMTA but less generally applicable. Characterises motional processes involving dipole reorientation. Mobile-phase content (hence crystallinity). Measurement of conducting polymers over complete working range. Definition of electrical quantities—dielectric permittivity and loss. 

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