Application Of Insulator-Metal Transition Of Conducting Polymers

As example of application of the insulator-metal transition in conducting polymers, electro-optic device utilizing electrochemical doping and radiation induced doping are discussed in detail.     

Surface Modification Of Conducting Particles. A New Approach To Conducting Polymers.

Conducting polymers based on binding a highly conducting inert inorganic solid and insulating polymer matrices have been prepared. Films prepared with the surface modified pigments exhibit surface conductivities comparable to and in some cases greater than those prepared from unmodified pigments.     

Highly Conducting Derivatives Of Polyacetylene And Poly-Pyrrole Formed In The Reaction With Selected Protonic Acids And Metal Halides - Synthesis And Application

Abstract

It has been found that polyacetylene can be used in chemical analysis for selective determination of nitrate ion in dilute aqueous solutions. If such solutions are acidified with sulphuric acid the log σ vs. NO₃ concentration plots are linear over the NO^? ₃ concentration range 2–40 mM. Several new conducting derivatives of chemically polymerized polypyrrole have been prepared in the reaction with selected metal halides such as: FeCl₃, SbC1₅, and others. The products have been characterized by elemental analysis and conductivity measurements.     

Role Of Geminate Recombination In Photovoltaic Spectral Responses Of Polyacetylene Junctions

Photoresponses of Schottky-type polyacetylene junctions are measured and compared with a theoretical model. Evidences for the importance of geminate recombination of photogenerated pairs are presented.     

Ultra High Vacuum Electrochemistry with Conducting Polymers

Solvent free polymer solid electrolytes based on high molecular weight poly(ethylene oxide) (PEO) complexed with alkali metal salts are compatible with ultra high vacuum (UHV). This has been taken advantage of in the design of electrochemical cells for electrochemical synthesis as well as reduction/oxidation of polypyrrole in UHV. This allows in situ application of surface spectroscopies (XPS) to study the material as a function of its state of oxidation.     

New Transport Mechanisms for Conducting Polymers: The Role of Disorder

Abstract

A unified view of the metallic state in polyaniline and heavily-doped polacetylene is presented. We first consider a single randomly-protonated strand of the emeraldine form of polyaniline. We show explicitly that the disorder inherent in this system is described by the random-dimer model of Dunlap, Wu and Phillips¹. The random dimer model is simply a tight-binding model for a binary alloy in which pairs of lattice sites are assigned one of two values at random. The random dimer model is shown to possess a narrow band of conducting states that can ultimately lead to dramatic increases in the conductivity if the Fermi level is appropriately tuned. It is demonstrated explicitly that the location in the energy band of the conducting states of the random-dimer model for polyaniline coincides with recent calculations of the location of the Fermi level in the protonated form of the polymer^2,3. We argue then that the random-dimer model is capable of explaining the insulator-metal transition in polyaniline. In the context of polyacetylene, we propose a ‘dirty metal’ picture for the metallic state which is consistent with both the closing of the band gap and the existence of a band of extended states. Our model is based on the observation that a random distribution of solitons closes the band gap at ～5-6% doping and is formally equivalent to the random dimer model. The location of the extended states in the disordered soliton lattice is computed. It is shown that because these states lie in the vicinity of the band edge, they are capable of explaining the sudden onset of the experimentally-observed Pauli susceptibility and the subsequent depinning of the solitons in the metallic state. We close by noting that because the random dimer model applies to any lattice in which the defects are extended and possess a plane of symmetry, it quite generally describes any polymeric system in which the stable defects are solitonic or bi-polaronic in nature     

Polypyrrole - Semiconductor photovoltaic devices

Abstract

A new approach is given for obtaining fast electro-optical response and good angular-viewing characteristics in a liquid-crystal variable-retardation device. The improved characteristics make the new device well suited for use in field-sequential color systems.     

Proton Magnetic Resonance in Partially Deuterated Trans - Polyacetylene

Proton NMR measurements as a function of ^l H concentration in partially deuterated trans-(CH_zD_1-z)_x show that at high ¹H content the proton relaxation is ^{z 1-z x}homogeneous and reflects the dynamics of electronic spins. At low concentration, protons of residual catalyst (about 6% per CH unit) dominate the NMR results, misleading earlier analysis.     

New Structural Phases of Polymer Battery Anode Materials: Alkali-Metal-Doped Polyacetylene and Polyphenylene

New ordered phases of alkali-metal complexes of polyacetylene and poly(p-phenylene) have been identified by x-ray diffraction studies and by quasi-equilibrium measurements of potential vs. composition during electrochemical reduction with Li+, Na+, and K+ counterions.     

Material Highlights: Liquid Crystal Polymers

Abstract

A key issue in the area of side chain liquid crystal polymers concerns the conformation of the backbone within the mesophase. In order to resolve this matter, Noirez and co-workers (Liquid Crystals, 1995, 18 129) have studied a wide range of polymers exhibiting both nematic and smectic behaviour using small angle neutron scattering. Their results combined with a survey of those in the literature reveal that if the polymer is solely nematogenic, then the backbone adopts a prolate conformation in which on average it lies along the director. By contrast, in a smectic phase the backbone adopts an oblate shape and on average lies perpendicularly with respect to the director. This arises from a microphase separation in which the backbones are distributed between the mesogenic layers. However, the backbones can cross the mesogenic layers although their ability t o do so depends on, amongst other factors, the degree of polymerization. If the polymer exhibits both nematic and smectic behaviour, then in the nematic phase the backbone adopts a slightly oblate shape resulting from smectic fluctuations.     

Surface Chemistry of Polyacetylene: Adhesion to Silica,Derivatization With Nickel And Catalytic Activity

Adhesion of (CH)_x film prepared by the Luttinger method to glass can be improved by silylation in order to more closely match dispersive surface energies. Treatment of n-type (CH) films with NiBr₂/HMPA/THF affords (CH)_x -supported N° which shows selectivity in hydrogenation of phenyl acetylene.     

Reversible and Non Reversible Oxidation of Polyacetylene In Aqueous and Non Aqueous Media : An Electrochemical Study

Cyclic voltammetry has been applied to study the reversibility of the oxidation of polyacetylene in sulfuric acid solutions and in lithium salts - nitromethane solutions. The intensity-potential curves indicate generally two steps of oxidation : the first one, corresponding to the doping, is reversible and is characterized by a dramatic increase of the electrical conductivity; the second one, called overoxidation, is due to the irreversible destruction of the carbon-carbon double bonds by formation of sp3 carbon atoms and is evidenced by the lowering of the conductivity.     

The Metallic State of Doped Conjugated Polymers: ESR Studies

We present ESR results obtained on highly doped polyacetylene and polyphenylene which bring some light on the magnetic and electronic properties of these systems, which are commonly assimilated to metals. We analyze the existing experimental data in terms of coexistence of Curie and Pauli type behaviours, and we show that ESR in the metallic state can be used to gain information on the dynamic properties of the electronic system.     

Liquid Crystal Polymers: Conformation of Deuterated Parts by SANS

Comb like liquid crystal polymers are polymers on each monomer is grafted a hanging liquid crystal molecule. The bulk state has the classical liquid crystal phases (nematic, smectic); what is the conformation of a chain in these phases is the problem to solve with the help of small angle neutron scattering. The values of the global sizes R _|| and R _‖ of a chain (in the direction parallel and perpendicular to the director) are discussed as a function of the chemical species and the temperature. Strange results are discussed in terms of segregation of labelled parts.     

直流反应磁控溅射法制备ZnO: Zr透明导电薄膜

以Zn∶ Zr为靶材,利用直流反应磁控溅射法制备了ZnO∶ Zr透明导电薄薄膜.研究了沉积压强对ZnO∶ Zr薄膜形貌、结构、光学及电学性能的影响.实验结果表明所制备的ZnO∶ Zr为六方纤锌矿结构的多晶薄膜,具有垂直于衬底方向的c轴择优取向.沉积压强对ZnO∶ Zr薄膜的晶化程度、形貌、生长速率和电阻率影响很大,而对其光学性能如透光率、光学带隙及折射率影响不大.当沉积压强为2Pa时,ZnO∶ Zr薄膜的电阻率达到最小值2.0×10-3Ω ·cm,其可见光平均透过率和平均折射率分别为83.2％和1.97.     

Tri-metal Secondary Building Units: Toward the Design of Thermally Robust Crystalline Coordination Polymers

Abstract Three new crystalline coordination polymers [Mn₃(TDC)₄(H₂O)₄](2,6-lutidine)₂(H₂O)₃ 1, P-1, a = 11.351(3), b = 11.391(3), c = 11.480(3), α = 112.838(4), β = 90.696(4), γ = 99.328(4); [Zn₃(1,4-BDC)₃(EtOH)₂] 2, C2/c, a = 19.1308(9), b = 10.6088(5), c = 16.2221(7), β = 108.79(1); and [Zn₃(1,3-BDC)₃(py)₂](MeOH) 3, P2(1)/c, a = 17.142(3), b = 21.544(4), c = 11.805(2), β = 106.441(3); TDC = 2,5-thiophenedicarboxylate, BDC = benzedicarboxylate, have been synthesized by linking tri-metal nodes with poly-carboxylate ligands. Single crystal x-ray analysis shows that 1 is composed of (4,4) 2-D grids with A–A stacking while 2 is comprised of (6,3) triangular networks in an A–B–C stacking pattern and 3 has formed a distorted cubic diamondoid topology. Tri-metal nodes are located at the vertexes of each network. Thermal gravimetric analysis demonstrates that 1 and 2 are thermally robust structures with network decomposition temperatures of 375 °C and 460 °C respectively. Graphical abstract Tri-metal Secondary Building Units: Toward the Design of Thermally Robust Crystalline Coordination Polymers Brian S. Luisi, Zhenbo Ma and Brian Moulton* Tri-metal nodes are shown to be an advantageous target in the synthesis of 2-D crystalline coordination polymers with high thermal stability.      

Epr Study of Polarons In a Conducting Polymer With Nondegen-Erate Ground States: asF5 Complexes of Poly(p-phenylene)

EPR measurements of temperature-dependent susceptibility and linewidth are reported for poly(p-phenylene) as a function of exposure time to dopant. Most of the charge is in bipolarons, rather than in the spin-associated polarons. Observed decreases in high temperature spin concentration as a function of doping time and post-doping anneal likely arise from both polaron-polaron reaction and polaron ionization to form bipolarons. The susceptibility of all the investigated AsF₅-doped samples strongly deviate from Curie-Weiss behavior at low temperatures. The observed temperature dependence can be explained by the low-temperature condensation of isolated polarons to form intermolecular polaron pairs in singlet ground states. The interaction between spins is antiferro-magnetic and the energy of the singlet-state polaron pair relative to two isolated polarons (-2.4 to -4.8 meV) is similar to that for the n-doped polymer (-2.4 to -2.7 meV).