CPCM

Conducting polymer composite materials (CPCM) — artificial media based on polymers and conductive fillers, have been known since the early 1940s and widely used in various branches of science and technology. Their properties are described in a considerable number of monographs and articles [1-12]. However, the publications available do not clearly distinguish such materials from other composites and do not provide for specific features of their formation. 

The main feature of the CPCM is a drastic difference between electric conductivity of a polymer matrix and the filler reaching a factor of 1024 in terms of resistivity (Fig. 1). There is no such difference in relation to any other physical property of com-... 

The CPCM constituents are a conducting filler and polymer matrix where this filler is dispersed randomly. 

Almost any known polymer or polymer mixture can be used in the capacity of a polymer matrix various additives may be introduced in the matrix to reduce melt viscosity, increase thermal stability of the composition or its plasticity, etc. A choice of a matrix is determined mainly by the operating conditions of a material and the desired physical-mechanical properties of a composite. One may state rather confidently that, other things being equal, the value of the CPCM conductivity does not depend on a choice of a polymer matrix [3]. 

The percolation theory [5, 20-23] is the most adequate for the description of an abstract model of the CPCM. As the majority of polymers are typical insulators, the probability of transfer of current carriers between two conductive points isolated from each other by an interlayer of the polymer decreases exponentially with the growth of gap lg (the tunnel effect) and is other than zero only for lg < 100 A. For this reason, the transfer of current through macroscopic (compared to the sample size) distances can be effected via the contacting-particles chains. Calculation of the probability of the formation of such chains is the subject of the percolation theory. It should be noted that the concept of contact is not just for the particles in direct contact with each other but, apparently, implies convergence of the particles to distances at which the probability of transfer of current carriers between them becomes other than zero. 

Experimental dependences of conductivity cr of the CPCM on conducting filler concentration have, as a rule, the form predicted by the percolation theory (Fig. 2, [24]). With small values of C, a of the composite is close to the conductivity of a pure polymer. In the threshold concentration region when a macroscopic conducting chain appears for the first time, the conductivity of a composite material (CM) drastically rises (resistivity Qv drops sharply) and then slowly increases practically according to the linear law due to an increase in the number of conducting chains. 

The defects caused by the high contact resistance especially manifest themselves in the metal-filled composites where the value of the percolation threshold may reach 0.5 to 0.6 [30]. This is caused by the oxidation of the metal particles in the process of CPCM manufacture. For this reason, only noble metals Ag and Au, and, to a lesser extent, Ni are suitable for the use as fillers for highly conductive cements used in the production of radioelectronic equipment [32]. 

The CPCM structure also determines the following properties important in practice the temperature coefficient of resistance, dependence of conductivity on frequency, etc. However, the scope of this review does not include the consideration of such dependences and they can be found in [2, 3,12]. 

Any review devoted to conducting composites would be incomplete if the application fields of such composites were not described even if briefly. One of the first, if not the foremost, examples of the utilization of the CPCM is antistatic materials [1], For the materials of this kind resistivity q of less than 106 to 108 Ohm cm is not required, and this is achieved by introducing small amounts (several per cent) of a conducting filler, say, carbon black [4],... 

The idea of using CPCM for shielding is rather alluring. Indeed, a casing of an article or instrument manufactured of such a material serves at the same time as a screen to protect against electromagnetic radiation. All the above-described operations involved in applying additional layers become unnecessary. 

Solvatochromic shifts for cytosine have also been calculated with a variety of methods (see Table 11-7). Shukla and Lesczynski [215] studied clusters of cytosine and three water molecules with CIS and TDDFT methods to obtain solvatochromic shifts. More sophisticated calculations have appeared recently. Valiev and Kowalski used a coupled cluster and classical molecular dynamics approach to calculate the solvatochromic shifts of the excited states of cytosine in the native DNA environment. Blancafort and coworkers [216] used a CASPT2 approach combined with the conductor version of the polarizable continuous (CPCM) model. All of these methods predict that the first three excited states are blue-shifted. S i, which is a nn state, is blue-shifted by 0.1-0.2 eV in water and 0.25 eV in native DNA. S2 and S3 are both rnt states and, as expected, the shift is bigger, 0.4-0.6eV for S2 and 0.3-0.8 eV for S3. S2 is predicted to be blue-shifted by 0.54 eV in native DNA. 

For the small system involved in the water exchange on [Be(H20)4]2+, we evaluated the effect of an implicit and approximated explicit treatment of the bulk water while investigating water exchange on [Be(H20)4]2+. For the implicit treatment, the CPCM and PCM models were applied as implemented in Gaussian, and geometry optimizations and... 

A structural comparison of the calculated (B3LYP/6-311+G ) ts (transition state in the gas phase), ts-wc (transition state in the cluster of five extra water molecules), ts-CPCM (transition state within the CPCM-solvent model (B3LYP(CPCM)/6-311+G )) and ts-PCM (transition state optimized within the PCM-solvent model (B3LYP(PCM)/6-311+G )), shows no large differences (see Fig. 8), which is also valid for the precursor complexes (see Fig. 9). Modeling solvent effects shrinks in all cases the Be-0 bonds of the entering/leaving water molecules (159). 

While the transition states could all be confirmed as transition states, only the precursor in the gas phase pc, and for the water cluster approach pc-wc, was confirmed as a local minimum, and despite intensive search no minima could be found within the CPCM and PCM model approximation. 

Fig. 13. Reaction profile for DMSO exchange on solvated Li+ enthalpy B3LYP(CPCM)/6-311+G including thermodynamic contributions at B3LYP/LANL2DZp gas-phase energy values B3LYP/6-311+G including AZPE at B3LYP/LANL2DZp, in parentheses T.S. = transition state (92).

While the MP2(full)/6-311+G 7/B3LYP/6-311+G energies show typical discrepancies, the application of the IPCM- and CPCM-solvent models dramatically lowers the energy for the intermediate and the transition states. The barriers of 2.8 and 1.8kcalmol 1 corroborate the experimental findings for an efficient formation of a water coordinated Li+ complex. 

---