Crystalline and conductivity

The temperature dependent dc conductivity, o-qc (T), provides a direct probe of the macroscopic charge conduction through the less conducting regions. Recent advances in chemical processing have resulted in higher crystallinity and conductivity for conducting polymers. 

More recently, Raman spectroscopy has been used to investigate the vibrational spectroscopy of polymer Hquid crystals (46) (see Liquid crystalline materials), the kinetics of polymerization (47) (see Kinetic measurements), synthetic polymers and mbbers (48), and stress and strain in fibers and composites (49) (see Composite materials). The relationship between Raman spectra and the stmcture of conjugated and conducting polymers has been reviewed (50,51). In addition, a general review of ft-Raman studies of polymers has been pubUshed (52). 

The short-range order in a material is important in determining optoelectronic properties. For instance, x-ray and electron diffraction experiments performed on amorphous siHcon (i -Si) and germanium (a-Ge) have revealed that the nearest neighbor environments are approximately the same as those found in their crystalline counterparts (6) photoemission experiments performed on i -Si show that the DOS in valence and conduction bands are virtually identical to the corresponding crystal with the exception that the singularities (associated with periodicity) present in the latter are smeared out in the former. 

A phytochemical investigation of taxine in the yew has been conducted by Kuhn and Schafer, who have devised special methods for the detection, estimation and purification of the alkaloid. Masson states that Taxus canadensis contains an alkaloid giving the colour reactions of taxine but different from it in being crystalline and having m.p. 238-9° no ephedrine was present. 

The main advantage of PEO as a host is that it is chemically and electrochemically stable since it contains only strong unstrained C-O, C-C, and C-H bonds. The disadvantage is the inherent crystallinity, and considerable effort has gone into synthesizing all-amorphous polymer hosts. Unfortunately, with the bulk conductivity as the prime motivator, many amorphous polymer hosts incorporate organic functional groups which limit their practical application. Detailed accounts of many of the hosts synthesized have been reviewed [8, 32-36],... 

Figure 8. Effect on conductivity, heat of fusion (degree of crystallinity), and Tg of adding zeolite to PEO-UBF4. Adapted from B. kumar, L. G. Scanlon, J. Power Sources 1994, 52, 261.

In this article some literature studies together with studies conducted recently in our laboratories on the crystalline and molecular structure of polymorphic polymers are reviewed, also with the aim of showing possible influences of the polymorphism on the properties and, as a consequence, on the applications of polymeric materials. 

J.9 You are asked to identify compound X, which was extracted from a plant seized by customs inspectors. You run a number of tests and collect the following data. Compound X is a white, crystalline solid. An aqueous solution of X turns litmus red and conducts electricity poorly, even when X is present at appreciable concentrations. When you add sodium hydroxide to the solution a reaction takes place. A solution of the products of the reaction conducts electricity well. An elemental analysis of X shows that the mass percentage composition of the compound is 26.68% C and 2.239% H, with the remainder being oxygen. A mass spectrum of X yields a molar mass of 90.0 g-moF. (a) Write the empirical formula of X. (b) Write... 

However, another obstacle to high bulk conductivity of such a polymer exists. In view of the hnite length and vast number of constitutive polymer chains, bulk conduction requires electrons to jump between chains (or polarons to transfer between chains in the opposite direction). It is obvious, then, that local order, crystallinity, and good contact between the different crystal domains in the polymer are further prerequisites for conduction. 

Atkins, J. R., Sides, C. R., Greager, S. E., Harris, J. L., Pennington, W. T., Thomas, B. H. and DesMarteau, D. D. 2003. Effect of equivalent weight on water sorption, PTFE-like crystallinity, and ionic conductivity in bis[(perfluoroalkyl) sulfonyl] imide perfluorinated ionomers. Journal of New Materials for Electrochemical Systems 6 9-15. 

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