Conducting polymers disorder

Conducting polymer composite materials are typical disordered structures consisting of randomly (or according to a certain law) arranged particles of a conducting filler that are submerged into a polymer medium. In this case the filler particles have macro-... 

Polymer science is underdeveloped in terms of descriptions of the structure and properties of stiff-chain polymers. The conducting polymers fall mostly within this blind spot. They also present a number of novel possibilities such as the conversion from a flexible-chain precursor to a rigid-chain polymer, and the conversion between doped and undoped states in the soluble polythiophenes. Likewise, solid-state physics has yet really to tackle the transport of electrons in, and between, disordered, twisted chains. For each of the disciplines involved, the explosion of interest in conducting polymers has brouht a host of new question and new ideas. The process is far from over. 

In undoped conducting polymers [cr(300 K) < 10-6 S/cm], S (300 K) 1 mVK-1. This value decreases upon doping, and in fully doped systems S (300 K) 10 pV K-1. Although conducting polymers are intrinsically quasi-ID and highly disordered, a remarkable linear S(T) has been observed in high quality metallic samples down to 10 K [16,21]. This indicates that the thermal current carried by phonons is less impeded by insulating barriers... 

Key Words Dipolar glasses, Ferroelectric relaxors, Conducting polymers, NMR line shape, Disorder, Local polarization related to the line shape, Symmetric/asymmetric quadrupole-perturbed NMR, H-bonded systems, Spin-lattice relaxation, Edwards-Anderson order parameter, Dimensionality of conduction, Proton, Deuteron tunnelling. 

Disordered systems can be broadly classified into spin glasses, dipolar glasses/pseudo-spin glasses, canonical glasses, conducting polymers (CPs),... 

Fig. VI-3 shows a schematie diagram of the electrical conductivity vs. temperature (In tr vs. In T) in the vicinity of the metal-insulator transition. Each of the curves shown in Fig. VI-3 is drawn for a different degree of disorder for a given conducting polymer system, each curve would represent data obtained from a sample with different resistivity ratio, Precisely at the critical point (where the mobility edge is precisely at the Fermi energy), the conductivity follows the power law of Eqn VI-6. On the metallic side, the resistivity remains finite as the temperature approaches zero as indicated in Eqn VI-5. On the insulating side, the resistivity falls below the power law as a result of the exponential dependence that results from variable range hopping see Eqn VI-8 and VI-9.

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