An Insight on the Polyacetylene Properties Through Resonant Raman Scattering Spectra Analysis

Resonant Raman Scattering spectra of trans polyace-tylene (CH)_X and (CD)_X are interpreted in terms of a model based on a bimodal distribution of conjugation length segments. Such a theory takes into account the electronic and lattice dynamics properties of different conjugation length segments, together with the electronic dipole moments from the transitions and the electron vibration interactions in the excited electronic states. This model accounts also for the Resonant Raman Scattering spectra taken during the isomerization process and from cis rich samples.     

Relationship Between Structure and Properties for Donor-Doped and for Acceptor-Doped Polyacetylene

Two basic structural types are experimentally derived for polyacetylene complexes: channel structures (Na, K, Rb, and Cs) and layered structures (iodine and a variety of other acceptors). Observed variants for the layered structures include first-stage and higher-stage complexes, with either complete or fractional occupation of dopant on the dopant-containing planes. A third structural type, in which dopant is statistically distributed, is predicted up to high dopant levels for lithium dopant. These structural results are used to explain observed properties and to predict properties obtainable for nearly defect-free single crystals. Discussions will include the structural origin of electrochemical discharge curves, major increases in conductivity on annealing K-doped and Rb-doped polyacetylene, the extremely high thermal stability of alkali metal channel complexes, and predicted mechanicals and transport properties for single-crystal complexes.     

Frequency Dependent Conductivity of Polyacetylene

We report on an extensive study of the frequency and temperature dependent conductivity of largely cis- (CH)_x trans- (CH)_x, and NH₃ compensated and iodine doped materials. The results reveal a strongly temperature (T) dependent dc conductivity and weakly T-dependent ac conductivity for largely cis- (CH)_x and for NH₃ compensated samples, similar to the behavior that is observed in many crystalline and amorphous semiconductors. The trans- (CH)_x and lightly iodine doped trans- (CH)_x have larger dc and ac conductivity and a strongly T-dependent ac conductivity. These latter results contrast with the usual expectations of variable range hopping and polaronic hopping, but are in good agreement with the predictions of Kivelson's Theory of charge transport via intersoliton electron hopping.     

Thermal Isomerization of Polyacetylene Films

Isomerization of the as-formed (-78°C) cis-polyacetylene to the trans isomer is relevant to the electronic structure, the crystal structure and the electrical properties of this prototypical conductive polymer. We have studied the process using Fourier transform infrared (FTIR) and 13_C magic angle nuclear magnetic resonance (NMR) spectroscopies at temperatures between 80 and 110°C. The observed kinetics will be discussed in terms of three basic processes: a second order process which randomly converts cis-cis-cis (CCC) sequences to trans-cis-trans (TCT) sequences via a pair of biradicals, a fourth order process that converts CTCC sequences to TCTT sequences via four biradicals, and two fourth order processes which allow sequential migration along the chain. The correlation of observed electron spin resonance and x-ray results, among others, with these mechanisms will be shown.     

Infrared Absorption of Doped Polyacetylene

The frequency dependent conductivity of added charge (e.g. solitons) to a dimerized Peieres condensate with N coupled phonons is studied. The electron-Phonon system, with electron -electron interactions and pinning effects, yields in the adiabatic and continuum limits an infrared absprption whose structure is independent of the charge configuration. The kinetic mass of the charge affects only the pinning parameter and the over-all magnitude of the absorption. This mass is es timated from experimental data and compared with theoretical soliton and polaron masses.     

Structure and Properties of Nanostructured SZO Films Obtained by Electron-Beam Evaporation

Crystallography Reports - The composition, structure and properties, as well as the current–voltage characteristics (CVCs) of nanostructured SZO films were studied. These films were...     

Lattice Dynamical Calculations of Trans and Cis Polyacetylene

Lattice dynamical calculations of the lattice modes for both trans and cis polyacetylene were performed. Using rigid body approximation for the chain we obtained all 8 lattice frequencies and modes of motion for both trans and cis polyacetylene. The frequencies concerned with Raman active lattice modes are presented for the first time. We also performed far infrared transmission measurements of undoped trans and cis polyacetylene and confirmed the results obtained by Bechtold et al. Comparison of the lattice frequencies obtained by lattice dynamical calculations with the results obtained by far infrared measurement and inelastic neutron scattering is discussed.     

On Trapping of Phase Kinks in Polyacetylene

A microscopic mechanism for trapping of solitons in polyacetylene is given. Molecular orbital calculations with full geom ety optimizaiton using semi-empirical tight.binding Hamiltonian for finite chain indicate that the neutral spin-carying phase kink is attracted by an energy on the meV scale to carbon atoms having a non-hydrogen side- group in accordance with recent magne tic resonance experiments. The oxygen induced trapping of the spins is also discussed.     

Transport,Magnetic and Structural Studies of Polyacetylene

Experimental progress is reviewed with emphasis on magnetic and transport studies. The magnetic results are fully consistent with the soliton doping mechanism; the decrease in Curie-law contribution has been demonstrated; the Pauli term remains small (Y < 0.07) and is apparently zero in the limit of completely uniform doping. The electrical conductivity (P and T dependence) and thermopower (n-type and p-type) are in excellent agreement with Kivelson's theory of intersoliton electron hopping.     

Distribution of Iodine in Doped Polyacetylene Filme

The distribution of iodine in polyacetylene doped under conditons typical for most published work is investigated by energy dispersive X-ray analysis under an electron microscope. The 9.1 GHz dielectric constant of a series of iodine doped (CH)_x is measured as a function of temperature. From the X-ray analysis we conclude that the reaction takes place in two steps: a fast reaction at the fiber surfaces and a slow reaction with the interior of (CH)_x fibers. The dielectric dconstant of lightly doped (CH)_x in the interior of the fibers. The temperature dependence of ε is believed to be related to the intrinsic temperatue dependence of the conductivity of the highly doped fiber surface layers.     

Structural Investigations of Polyacetylene and Polyphenylene by Neutron Scattering

Wide angle neutron scattring patterns of deuterated cis- and trans-polyacetylene (PA) and deuterated polyphenylene (PPh) doped with AsF₅ have been measured. For undoped trans-PA a refined crystal structure is proposed to reproduce the neurtron scattering data. Doping of PA with AsF₅ is explained on the basis of an intercalation model. Deuterated PPh has been prepared by different polyerisation procedures, variing the crystallinity of the undoped material in a wide range. Strong extra peaks are observed during doping with AsF₅, wheres the crystallinity of the samples remains essentially unchanged. An intercalation model similar to AsF₅.-doped graphite is proposed.     

Absence of Knight-Sheft in the Metallic State of Polyacetylene

NMR spectra on ¹⁸C of cis-(CH)_x have been recorded using the magic angle spinning technique. Inspite of doping with AsF₅ up to a level of ～ 7at%, (CH)_x does not convert to the trans modification. No Knight shift or other line shift is observed up to this dopant concentrtion. Above 7at% a line shift of about 30 ppm is found. To extend the soliton model to cis-(CH)_x bi-solitons or bi-polarons are proposed.     

Theoretical Investigation of Impurities and Intercain Coupling in Polyacetylene

In this work we study the efect of the interchain coupling on the electronic density of states in polyacetylene. First we show that a localized interchain coupling can be simulated by a single substitutional impurity scattering and introduces four symmetrical bound levels at the band edges. We then study the evolution of these levels in the presence of a soliton on the chains. Finally we consder a two- dimensional distribution of interchain interwactions and study its effect on the broadening of the band edges. It is found that, when this coupling is taken into acount, the semi conductormetal transition found in charged soliton-Lattices may occur at a concentration of solitons c ～ 5%.     

Electron Hopping Conduction in the Soliton Model of Polyacetylene

It is shown that at low temperatures a novel conduction mechanism, phonon assisted hopping between soliton bound states (intersoliton hopping), may be the dominant conduction process in lightly doped polyacetylene. The theory is developed from a more general phenomenological viewpoint than previously, and the model independent aspects of the transport are stressed. It is found that the theory successfully accounts for experiments in polyacetylene which simultaneously show the hallmarks of solitons (e.g. no increase in the number of spins upon doping, a highly one-dimensional spin mobility, a qualitative dependence on cis to trans isomerization) and the characteristics of hopping transport (e.g. a strongly frequency and electric field dependent conductivity). It is further suggested that, since the theoretical considerations that lead to the conclusion that intersoliton hopping is important in polyacetylene are quite general, the same basic transport process may be important in many quasi-one dimensional semiconductors.     

The Influence of Polyurethane Component on the Properties of Polyurethane-Rubber Composites Obtained from Waste Materials

Properties of the polyurethane-rubber composites obtained from used products were studied. The influence of the amount of polyurethane glue and amount of isocyanate diphenylmethane 4,4′-diisocyanate (MDI) on composites selected properties was observed.

The dynamic thermo-mechanical analysis allowed us to determine the glass transition temperature Tg and the course of the relaxation processes in the composites. The analysis of the changes in the storage module E′ and loss module E^″ as a function of temperature enabled the calculation of the activation energy for relaxation processes of various polyurethane glues and polyurethane-rubber composites.     

Theoretical Studies of Charged Defect States in Doped Polyacetylene and Polyparaphenylene

Defect statecalculations have been per formed for polyacetylene and polybparaphenylene in the fraamework of the Su, schriever, and Heeger Hamiltonian. In polyacetylene, the study of the energetics of the separation of the radical(natural defect)-ion(charged defect) pair induced upon doping indicates that the two defects tend to remain close to each other. This results in the formatn of polarons whose binding energy is estimated to be of the order of 0.05 eV Absorption spectra at low doping levels are consistent with polaron formation. Interaction between polarons leads to the formation of charged solitions. In poly(p-phenylene), defects are always correlated in pairs. Upn doping, polarons are formed (binding energy ～ 0.03 eV), wit the relaxation of the lattice extending over about four rings. Calculations suggest the possibility of bipolarons (doubly charged defects) that yield conductivity without Pauli susceptibility.     

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.     

Structural Changes of Doped Polyacetylene During The Electrochemical Charge and Discharge Process

Results of in situ Raman scattering during the electrochemical p-doping of cis-and trans-polyacetylene are reported. Doping the cis-isomer led to a complete cis-trans isomerization. During the discharge process, a down-shift of the Raman line for the C=C stretch mode without any increase of intensity was observed. Starting the doping process with trans-polyacetylene, the disordered parts dope first whereas the crystalline parts undope first.     

Microanalysis of the SmS Films Obtained by Magnetron Sputtering of a Target

Crystallography Reports - The thin SmS films obtained by magnetron sputtering of a SmS target with the 1.3Sm:1S composition have been investigated. The microanalysis of the sputtered target has...     

A Novel Method for Study of a Smectic Phase Obtained from a Strongly-Deformed Nematic Texture

A simple method for the growth of conventional or reentrant smectic phases from strongly-deformed conventional or reentrant nematics, is proposed. It permits the formation of surface-induced and surface-governed conventional and/or reentrant smectic textures which can be studied from the scientific point of view or can be applied in the laser-addressed thermo-optic smectic liquid crystal storage displays for the creation of static figures. The simple method proposed might be applied for study of many smectics arrising either from conventional or reentrant nematic phases under cooling or heating.