J.K. Jeszka

Superconductivity in reticulate doped polycarbonate films, containing (BEDT-TTF)2I3

Abstract Electric properties of conducting reticulate doped polymeric films, containing ET polyiodide crystalline network, have been investigated. In order to improve their conducting properties they were annealed in iodine vapors. It was found, that certain conditions of thermal treatment lead to metal-like state, stable down to helium temperatures. The overall decrease of resistivity R 300K /R 4.2K reaches 45. At some conditions of the thermal treatment an accelerated decrease of resistivity is observed below 7 K, vanishing with application of magnetic field, thus giving the first evidence of the (incomplete) superconducting transition in polymeric organic composite material.

Properties and microstructure of crystalline BEDT-TTF polyiodide network in polycarbonate matrix

A conducting network of crystalline [bis(ethylenodithio)tetrathiafulvalene]2I3 (ET2I3) can be formed within the surface layer of polycarbonate by exposure of films containing 2 wt.% of molecularly dispersed ET to vapours of iodine solution in CH2Cl2, THF or TCE. The relationship between the microstructure and properties of conducting networks formed under different conditions is reported. Depending on the iodine concentration in the solution, the kind of solvent and the treatment time, networks of a-ET2I3 or β-ET2I3 crystallites are formed. Their preferential orientation (c-axis perpendicular to the film plane) can be deduced from X-ray diffraction. Morphological studies performed using a scanning electron microscope revealed a nanoscopic size of crystallites and different habits: plate-like or river-stone-like. The presence of a less organised layer covering the crystallites, possibly formed of salts of another composition, is also discussed. The conductivity of the films is higher than that reported for polycrystalline layers obtained by the evaporation method and for pressed pellets of ET2I3. Films with a-ET2I3 show semiconducting behaviour with some deviation of the temperature dependence of conductivity at 160–200 K. Films with β-ET2I3 show metallic conductivity down to 60 K. Studies of the optical absorption have shown that the conducting network does not contribute much to the UV-VIS spectra of conducting films.

New transparent, colorless, metallically conductive polymer films and their electrochemical transformations

New surface conductive polymer composite films exhibiting extraordinary properties: high conductivity with metallic temperature dependence and exceptionally high transparency are presented. The conducting networks in these materials are formed of plate-like nanocrystals of bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) salts with iodine or bromine. The films with bromine salts are colorless and transparent while those with iodine are colored. It is demonstrated that colored films with (BEDO-TTF)/iodine networks can be electrochemically transformed into highly transparent, practically colorless materials without deterioration of the conducting network. The resulting metallically conducting polymer materials show the highest transparency among conductive composites reported so far.

Metallic polymer composites with bis(ethylenedioxy)-tetrathiafulvalene salts. Preparation–properties relationship

Abstract The relationship between preparation conditions and properties of surface-conductive composites obtained by crystallization of low molecular weight organic conductors in polymer matrices (reticulate doped polymers) is investigated. By optimization of the preparation procedure we have obtained the first organic conductive composites which show metallic surface conductivity without any additional treatment. Surface-conductive polycarbonate (PC) films with bis(ethylenedioxy)-tetrathiafulvalene (BEDO-TTF) salts with iodine and bromine as the additives were obtained by the two-step reticulate doping method. BEDO-TTF content in PC was 1 wt.%. Due to the strong tendency of BEDO-TTF to form organic metals the films obtained under optimum conditions show exceptionally high surface conductivity (even above 10−3 S/□ for both I and Br salts), and exhibit metal-like temperature dependence of conductivity in a broad temperature range (even down to at least 10 K). Depending on the preparation conditions (vapour composition, treatment time) it is also possible to obtain highly conductive films showing semiconductor-like temperature dependence or metal–insulator transition. Structure and morphology of the conductive network is characterized using scanning electron microscopy and X-ray diffraction. These results and optical absorption studies permit identification of the salts which are main components of the networks in most of the systems. When the conductive network is made of BEDO-TTF/Br salts the films show also exceptionally high transparency.

Stoichiometry of the CT complex crystallites in polymer films

The stoichiometry of the charge transfer (CT) complex which crystallised in a polymer solution during film casting has been studied by a spectrophotometric method. It was found that the donor-to-acceptor molar ratio changes from 1:2 to 1:1 and even more, depending on the film casting conditions. The composition of the CT complex crystals is also related to the morphology of the crystallites formed which strongly influence the properties of the doped films.

Submicroscopic structure of the TTT-TCNQ conductive network in reticulate-doped polymers revealed by SEM

Abstract The results obtained using high-voltage scanning electron microscopy (SEM), which enables observation of the structure of the conductive network within the surface layer of reticulate-doped polymer films, are reported. The submicroscopic structure of the tetrathiotetracene-tetracyanoquinodimethane (TTT-TCNQ) network in amorphous polymers is presented and its implications for the conductivity mechanism are discussed. The SEM pictures obtained reveal the fibrous internal structure of the conductive network in bulk-conductive films obtained using the amorphous polymers polycarbonate and poly(methylmethacrylate). TTT-TCNQ crystallites in the surface-conductive film have a different form in spite of the same polymer being used as the matrix.

Electrical Properties of Polymers Doped with Charge Transfer Complexes Forming Additives

Abstract Because of their good mechanical and processing properties as well as their low price, polymers have replaced such traditional materials as metal and wood in many fields of application. However, they lack one important characteristic-they do not conduct electricity. As with practically all organic substances known to date, they are usually good insulators; only a few categories can be classified as semiconductors. Materials which display higher conductivity can be obtained by synthesizing different polymers with a conjugated or aromatic backbone chain [1], but such materials, although classified as macromolecular, do not show the properties that would make polymers attractive from the point of view of application. Being poorly soluble, brittle, and melting at high temperatures, usually with decomposition, they are interesting practically only from the theoretical point of view.

Nanoscale morphology of melt crystallized polyethylene/graphite (HOPG) interphase

High density polyethylene (PE) was crystallised from the melt on freshly cleaved surface of highly oriented pyrolitic graphite (HOPG) or mica. Atomic force microscopy (AFM) studies of structure of the polymer surface adjacent to the graphite or mica were performed after peeling of from the substrate. Significant differences of crystalline structure on the interface were found between PE crystallised on graphite and mica. The surface of polyethylene crystallised on graphite shows large areas with regularly arranged rectangular structures. These objects (ca 20-80 nm big) probably represent the nucleation centres of the lamellar growth. The surface of polyethylene crystallised at mica surface shows some dot-like structures showing no particular arrangement.

Structure and optical properties of polycarbonate films with microcrystallites of BEDT-TTF polyiodides

Abstract The morphology, structure and optical properties of thin layers of crystalline bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) polyiodides formed within the surface layer of polycarbonate film were investigated. The samples were obtained by exposing the polymer films containing 2 wt.% of molecularly dispersed ET to vapors of I 2 /CH 2 Cl 2 solutions of different I 2 concentration. X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that, depending on the preparation conditions, ET polyiodides form plate-like crystals, flakes and some less organized layer covering microcrystallites. In all cases only (001) reflexes attributed to the α-ET 2 I 3 phase were registered in the X-ray diffraction (XRD) experiments. Reaction of iodine with already formed crystals leads to new morphological structures. Using saturated iodine solutions the nonconducting polyiodides are formed which, under ambient conditions, undergo transformation into a stable conducting salt.

Properties of conductive polycarbonate films reticulate doped with MPht(TCNQ)2 and PrPht(TCNQ)2 salts: A highly-conductive form of PrPht-TCNQ by crystallization in a polymer matrix

Abstract Conductive polymer films obtained by reticulate doping with N -methyl phthalazinum (MPht) and N -propyl phthalazinum (PrPht) TCNQ complex salts are investigated. It is found that the spectral, electrical and magnetic properties of the MPht(TCNQ) 2 in a polymer matrix are not significantly different from the properties of single crystals, while in the case of PrPht a new highly-conductive form is obtained by rapid crystallization during film casting. It is concluded that the dimerization of the TCNQ stacks in the new form is not as strong but the disorder is higher as compared with single crystals of PrPht(TCNQ) 2 . It is possible that the stoichiometry is also different.