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In this review we present the results of our literature investigation into the electrical and thermal properties of carbon nanotube polymer composites. A short selection of data relating to conductive polymer composites with various fillers is provided for comparison. The effects of filler properties such as type and size, the use of hybrid fillers, fabrication methods for polymer composites and the importance of the modeling of the electronic and thermal transport mechanisms are discussed, as are more general factors influencing the properties of these composites. This review represents a comprehensive survey and constructive study and should serve as a useful reference tool for industrial and academic researchers working in this field. [ABSTRACT FROM AUTHOR]

Abstract: The structure of a family of copolyimides in which are alternating stiff/redox pyromellitimide units and flexible/solvating polyethyleneoxide (PEO) strands were studied by using wide angle and small angle X-ray scattering techniques and is fully discussed. It is shown that the rich variety of structures exhibited by these compounds can be understood by considering the dramatic change of flexibility of the chain induced by the variation of the length of the PEO strand compared to that of the pyromellimide segment. In this respect, concerning the compounds which exhibit fully amorphous structures a better understanding of their structural behavior can be obtained in the framework of Flory''s theory of semi-rigid polymers. In this approach, the degree of flexibility of the chain is mainly resulting from the relative amount of flexible units constituting the repetition unit of the polymer chain. The final structural mode adopted by each compound in the solid state is then directly a consequence of this intrinsic property of the chain. The introduction of a lithium salt in contact with the copolymer chains induces some structure changes which can also be explained by the modification of the degree of flexibility of the chain. It is found that the best performances in terms of electroactivity and mixed conduction are precisely obtained with the only compound which keeps full amorphicity in absence and in presence of the lithium salt. [Copyright &y& Elsevier]

Hybrid poly(vinyl alcohol) and alginate membranes were investigated in the process of ethanol dehydration by pervaporation. As a filler, three types of particles containing iron element, i.e., hematite, magnetite, and iron(III) acetyloacetonate were used. The parameters describing transport properties and effectiveness of investigated membranes were evaluated. Additionally, the physico-chemical properties of the resulting membranes were studied. The influence of polymer matrix, choice of iron particles and their content in terms of effectiveness of membranes in the process of ethanol dehydration were considered. The results showed that hybrid alginate membranes were characterized by a better separation factor, while poly(vinyl alcohol) membranes by a better flux. The best parameters were obtained for membranes filled with 7 wt% of iron(III) acetyloacetonate. The separation factor and pervaporative separation index were equal to 19.69 and 15,998 g⋅m−2⋅h−1 for alginate membrane and 11.75 and 14,878 g⋅m−2⋅h−1 for poly(vinyl alcohol) membrane, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The effects of molecular weight and the processing conditions on the polymer supramolecular organisation, its morphology and charge carriers mobility have been investigated for regioregular poly(3-hexylthiophene) (RR-P3HT) thin layers used for the fabrication of field-effect transistors (FETs). The application of three distinctly different processing techniques (dip coating, spin coating and drop casting) together with polymers exhibiting different molecular weights, including previously unexplored molecular weight value (120kDa by SEC equal to 27kDa after the MALDI-TOF correction) enabled the separation of the influence of purely macromolecular factors from the morphological ones. It has been demonstrated that the chain length of the deposited polymer is the determining factor in the fabrication of layers with high carriers mobility which changes from 10−5 cm2/(Vs) for the shortest chains (Mn corrected=1kDa) to 0.04cm2/(Vs) for the longest ones (Mn corrected=27kDa). The changes of the film morphology cannot explain the dependence of the mobility on Mn. The observed relationship can be rationalized by considering the principal factors, intervening on three different levels: (i) on the molecular level the increase of the conjugation length with Mn is observed which leads to a higher mobility of the carriers along a single chain; (ii) on the supramolecular level the probability of the interchain charge carriers hopping is higher for longer chains since the number of low activation energy pathways for the crossing between chains grows with the increase of the chain length; (iii) on the mesoscopic level the connectivity between aggregations of higher mobility, for example, nanorods observed by AFM, is better assured for longer polymer chains. The product of these contributions results in an enhanced carriers mobility for layers fabricated from high molecular weight polymer fractions. The morphology of the RR-P3HT layers is strongly dependent on the processing method used. For high rate deposition techniques (spin coating) nanorod-type morphologies are obtained for low molecular weight polymers whereas fractions of high molecular weight give films with a granular morphology. For low deposition rate techniques (dip coating) the rod-like morphology persists even for films fabricated from the highest molecular weight fraction. Moreover, for layers obtained from intermediate polymer fractions (from 1.9 to 10.8kDa) the individual rod width is, within the experimental error, equal to the length of the polymer chain if the all trans conformation is assumed. The above observation implies that polymer chains are oriented perpendicularly to the rod long axis. GIXD investigations fully corroborate this hypothesis. The rod diameter in layers deposited using the highest molecular weight fraction (27kDa) is significantly lower than the length of the chain in the all trans conformation, suggesting chain folds via all trans–all cis–all trans sequence of conformation changes which would limit the rod diameter. [Copyright &y& Elsevier]

Abstract: Electrical transport properties of multiwalled carbon nanotube (MWCNT) polymer nanocomposites based on epoxy and high density polyethylene (HDPE) as matrices have been studied. The composites have been prepared from masterbatches by dilution. Low electrical percolation thresholds of 0.05 and 0.4vol.% of carbon nanotubes in epoxy and HDPE matrices were found respectively. The analysis of the temperature dependence of dc-conductivity shows that the charge transport is fully described as the combination in series of one-dimensional (1-D) and three-dimensional (3-D) variable range hopping (VRH) regimes. The transport is limited by the 1-D VRH regime in the low temperatures limit and by the 3-D VRH regime at room temperature. The analysis of the VRH parameters when the overall volume fraction of MWCNT decreases reveals two distinct situations. In the epoxy the local characteristics of the masterbatch remain practically unchanged and a percolating network is maintained even at very low volume fractions; in the HDPE matrix, the density of the MWCNT bundles packing decreases as revealed by the strong variation of the Mott temperature parameter. Our results indicate that amorphous polymers matrices give lower percolation thresholds than semicrystalline ones when a masterbatch dilution process is used. [Copyright &y& Elsevier]

Polyarylamine containing meta–para–para-aniline units in the main chain and meta–para-aniline units in the pendant chains was synthesized. The polymercan be oxidized to radical cations in chemical or electrochemicalways. The presence of meta-phenylenes in the polymerchemical structure allows for the ferromagnetic coupling of electronicspins, which leads to the formation of high spin states. Detailedpulsed-EPR study indicates that the S= 2 spin statewas reached for the best oxidation level. Quantitative magnetizationmeasurements reveal that the doped polymer contains mainly S= 2 spin states and a fraction of S=3/2 spin states. The efficiency of the oxidation was determined tobe 74%. To the best of our knowledge, this polymer is the first exampleof a linear doped polyarylamine combining such high spin states withhigh doping efficiency. [ABSTRACT FROM AUTHOR]