Magnetic properties of poly(3-hexylthiophene)

A room temperature ferromagnetic phase is observed in samples of poly(3-hexylthiophene) partially doped with ClO₄⁻. The magnetic behavior presents a strong dependence on the sample preparation conditions, in particular, a dependence with the final potential of the sample after reduction. The origin of the ferromagnetism is proposed to be associated with interactions between spin 1/2 polarons formed in the polymeric chain upon doping. The dependence of saturation and spontaneous magnetization as the function of the final potential after reduction shows a way to control the magnetic properties of this polymer.     

Nature of a high-conductivity state of poly(diphenylene phthalide)

For thin films prepared from non-conjugated polymer, including poly(diphenylene phthalide) (PDP), a rather enigmatic transition to a metal-like high-conductivity state is observed. The existing models of the HCS in wide-band polymers were examined. The main feature of these models is a significant (often highly improbable) rearrangement of the electronic structure of part of the macromolecules under the action of external factors (an electric field, light, injected electrons, etc.). The model of the HCS in PDP proposed in the current work is based on the results of studying the electron-acceptor properties of fragments of PDP macromolecules and the concepts of molecular electronics. Electron-acceptor unoccupied orbitals of the fragments of macromolecules and the corresponding energy levels are assumed to act as transport nodes for the resonance coherent tunneling of electrons. Since PDP has no intrinsic charge carriers, the key role in the formation of the HCS is played by the injection of electrons from the electrodes and, hence, the processes occurring in the interface. The resonance injection of electrons from the Fermi level of the electrode immediately onto the transport levels of the polymer is achieved due to the applied electric field, chemical connection of macromolecules to the electrodes, and ensuing modification of the interface dipole. The connection of PDP macromolecules to the electrodes occurs via defective hydroxyl and carboxyl groups. Carboxylate ions, which interact with the electrode metal, can also be formed because of the dissociative capture of injected electrons by phthalide cycles adjacent to the electrode. Since a conducting channel in a 1-μm-thick film should be composed of at least ten PDP macromolecules, it is necessary to assume that an efficient electron transfer occurs between macromolecules. The proposed concept was additionally substantiated by invoking the published data on the conductivity of DNA molecules and the field emission of electrons from metals coated with a PDP film.     

Magnetic fluid poly(ethylene glycol) with moderate anticancer activity

Poly(ethylene glycol) (PEG)-containing magnetic fluids - magnetite (Fe₃O₄) stabilized by sodium oleate - were prepared. Magnetic measurements confirmed superparamagnetic behaviour at room temperature. The structure of that kind of magnetic fluid was characterized using different techniques, including electron microscopy, photon cross correlation spectroscopy and small-angle neutron scattering, while the adsorption of PEG on magnetic particles was analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. From the in vitro toxicity tests it was found that a magnetic fluid containing PEG (MFPEG) partially inhibited the growth of cancerous B16 cells at the highest tested dose (2.1 mg/ml of Fe₃O₄ in MFPEG).     

Influence of absorbed moisture on desizing of poly(vinyl alcohol) on cotton fabrics during atmospheric pressure plasma jet treatment

This paper studies the influence of moisture absorption of cotton fabrics on the effectiveness of atmospheric pressure plasma jet (APPJ) on desizing of polyvinyl alcohol (PVA). Cotton fabrics with three different moisture regains (MR), namely 1.8%, 7.3%, and 28.4% corresponding to 10%, 65%, and 98% of relative humidity respectively, are treated for 16 s, 32 s, 48 s, and 64 s. X-ray photoelectron spectroscopy analysis indicates that the plasma treated PVA has higher oxygen concentration than the control. Mass loss results show that the fabric with the highest MR has the largest mass loss after 64 s plasma exposure. Solubility measurement reveals that the sample with the lowest MR has the highest desizing efficacy and the percent desizing ratio reaches 96% after 64 s exposure plus a 20 min hot wash, which is shown as clean as the unsized sample through scanning electron microscopy analysis. The yarn tensile strength test results show that APPJ has no negative effect on fabric tensile strength.     

Kinetics of the fluorescence of poly(N-vinylcarbazole) and poly(N-vinylcarbazole) with 2,4,7-trinitrofluorenone in the solid state

The fluorescence decay time measurements by the stroboscopic method have been made on films of amorphous poly(N-vinylcarbazole) (PVCA) and PVCA doped with 2,4,7-trinitrofluorenone (TNF). The obtained lifetimes of two excimer species have at 77 K and at 300 K values of about 43 ns and 9 ns, which are similar to other measurements. The kinetics of excimer fluorescence and energy transfer in PVCA films are described by a simple model of the Stern-Volmer type. It assumes the fast migration of localized singlet excitons and their trapping in two species of excimer traps.We propose a modified kinetic model for films of PVCA with TNF. In this model we assume besides the exciton migration and trapping on excimer and impurity traps also the direct energy transfer from two excimer species to charge transfer complexes of PVCA with TNF by the Förster dipole-dipole mechanism. The estimated critical distance of this transfer are about 10 Å.     

Magnetic ground state and electronic structure of CeRu(2)Al(10)

We present a combined theoretical and experimental study of the electronic structure for CeRu(2)Al(10) based on ab initio band structure calculations and x-ray photoemission spectroscopy (XPS) data. Our calculations were performed for the base unit cell and for the hypothetical unit cell which enables antiferromagnetic ordering. The stability of the magnetic phase was investigated within fixed spin moment calculations. When additional 4f correlations are not included in the LSDA C U approach, CeRu(2)Al(10) exhibits an unstable magnetic configuration with the difference in total energy per unit cell between the weakly magnetic state and the non-magnetic one of the order ~0.3 meV. We found that Coulomb correlations among 4f electrons, when they are included in the LSDA C U approach, stabilize the magnetic structure. In the weakly correlated system (small U) an antiferromagnetic (AFM) ground state with the lowest total energy is preferred. The situation is, however, the opposite when the 4f correlations are strong. In this case the ferromagnetic (FM) ground state is preferred. By comparing our calculations with the experimental data we conclude that the 4f correlations in CeRu(2)Al(10) are weak. We also carried out a structural relaxation of atomic positions within the Cmcm unit cell and we found that the Al atoms exhibit noticeable displacement from their positions known from x-ray diffraction (XRD) analysis.     

Luminescence of poly(N-vinylcarbazole) in the solution and solid state

Fluorescence spectra of poly(N-vinylcarbazole) have been studied as a function of various environments and temperature. Fluorescence spectra have been excited with UV light from 200 W Xenon lamp or with second-harmonics of a pulsed ruby laser. Polymer films and powders show exclusively excimer fluorescence at room temperature. At high intensities of excitation the observed fluorescence spectra have a weak quasiperiodic structure.     

Dependence of the GaAs (110) surface electronic state dispersion curves on the surface relaxation angle

The surface state dispersion curves E($\text{k}$) of the dangling bond states near the fundamental band gap, C₃ and A₅, are computed for both the established θ?27° model and the recently proposed θ?7° model of the (110) surface relaxation of GaAs, where θ is the surface bond rotation angle. The two models produce surface state dispersion curves that are similar to one another and to the data.     

SERS observation of the effects of pressure and water on the absorbed state of nitrogen dioxide on a silver powder surface

The effects of pressure and water on the adsorbed state of nitrogen dioxide on silver powder produced from an aqueous solution of AgNO₃ were studied by SERS. NO₂ of 10² Pa was added to the silver powder in the sample chamber and then pressure was raised up to ∼10⁵ Pa with dry Ar, N₂ or O₂. The observed surface species are NO₃⁻ and NO₂⁻ ions under atmospheric pressure. When the total pressure decreases, NO₂⁻ is transformed into NO₃⁻ and NO⁺. This reaction is reversible with the total pressure variation of dry gases regardless of kind. Once the silver powder adsorbing nitrogen oxides is exposed to moistened gas or air of ∼10⁵ Pa, the reversible variation was interrupted, and NO₃⁻ and NO₂⁻ ions are observed on the silver surface.     

State of water in sulfonated poly(vinyl fluoride) membranes: an FTIR study

The state of water in new types of polymer-based proton conductors has been characterized by FTIR spectroscopy. The materials were produced by sulfonation of poly(vinyl fluoride) (PVF) films with chlorosulfonic acid after electron beam or proton irradiation or without any preirradiation. Spectra in the O–H and O–D stretching regions and in the H–O–H (D–O–D) bending region were analyzed in terms of frequency position and relative intensity of the various components. We found that the state of water in the sulfonated PVF membranes (PVF–SA) membranes differs significantly from that of the bulk water, and both hydrogen-bonded and non-hydrogen-bonded water molecules were detected. It is also found that the materials display the presence of a large number of proton complexes such as H₃O⁺ or H₅O₂⁺. The study demonstrates furthermore that proton irradiation makes the material more hydrophilic than electron irradiation, which can be explained by the different nature of the irradiation effects.     

Sorption of water vapor into polyelectrolyte complex of poly(styrenesulfonic acid)/poly(4-vinyl-N-ethylpyridinium bromide)

Successive differential and integral sorptions of water vapor into the polyelectrolyte complex of poly (sty renesulfonic acid) / poly(4-vinyl-N-ethylpyridinum bromide) have been measured; films of stoichiometric (1/1 molar ratio) and nonstoichiometric (2/1 molar ratio) complex were employed in the experiments. Sorption isotherms have been also determined by using the values obtained from integral sorption experiments. The sorption data have suggested the following. (i) The rearrangement of polymer chains plays a relatively unimportant role in sorption of water. (ii) The relaxation motion of network chains is suppressed. (iii) The change of morphological structure caused by vapor sorption is obscure. (iv) The ionic character of the 1/1 complex is higher than that of 2/1 complex. (v) A small amount of water can be dispersed on specific polymer sites, but the sorption of a large amount of water is accompanied by an expansion of network structure. Points (i)-(v) have been consistently interpreted on the basis of the network structure and ionic character of this complex.     

The effect of absorbed water on hydronium NASICON and Hyceram

The bulk resistance of bonded hydronium NASICON, (Hyceram^TM), was studied at 45°C in relative humidities ranging from 40% to 100% in both H₂O/N₂ and D₂O/N₂ atmospheres. The bulk resistance was found to increase exponentially with decreasing relative humidity. In addition, the isotope effect remained close to 2.2 over the range of relative humidities tested; therefore proton hopping (Grotthus mechanism) was shown to be the dominant conduction mechanism from saturation down to 40% relative humidity. Saturated and desiccated samples of hydronium NASICON powder were prepared for X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The XRD patterns revealed that the change in the lattice plane spacings arising from the absorption of water was negligible. TGA showed that the x=1.5 form of hydronium NASICON contained at least 1.5 moles of absorbed water per mole of NASICON when saturated. In addition, the absorbed water was shown to be weakly held by the lattice since its evolution from the saturated sample was rapid. These XRD and TGA results suggested that the molecules of absorbed water occupy lattice sites which might afford considerable freedom of rotational and translational motion.     

腺嘌呤吸附在银胶上的SERS研究

研究了腺嘌呤水溶液吸附在银胶上的表面增强喇曼散射(SERS)。除在SERS谱和普通喇曼谱不是很大差异外,观察到腺嘌呤的SERS谱与在银胶中腺嘌呤的体浓度有关。在改变腺嘌呤体浓度时,腺嘌呤环呼振动模的峰值有位移和相对峰值强度改变,把它们诠释为腺嘌另在银面上的取向有关。     

Solid state NMR study of sodium thiocyanate/poly(ethylene oxide) electrolytes

¹H-, ¹³C-, ²³Na-solid state NMR measurements have been used to characterise the morphology and the dynamics of several NaSCN-PEO mixtures. Selective ¹³C-MAS experiments allowed to determine the composition of the (PEO)_nNaSCN samples in terms of the different phases present, as well as the real stoichiometry of the crystalline complex. ¹H- and ¹³C-spin-lattice relaxation times provided estimates of the dimensions of the different domains and gave information on the dynamics of the polymer chains. ²³Na-MAS spectra and 2D nutation experiments allowed to individuate the presence of different environments for the sodium cations on the basis of their quadrupolar interactions.     

Environmentally friendly films based on poly(3-hydroxybutyrate) and poly(lactic acid): A review

A review of data on the thermo, photo-, and biodegradation of compositions of synthetic polymers with poly-3-hydroxybutyrate and poly(lactic acid) is presented. The influence of these polymers on the thermal, microstructural, and rheological properties of mixtures is examined. The destruction of pure biopolymers, as well as compositions thereof with polyethylene, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate), and polycaprolactone is studied.     

Dependence of the lowest impurity state on alloy composition in GaAs-(Al,Ga)As quantum dots

The ground state donor binding energy is estimated using the simple first order perturbation method for a GaAs-Al _x Ga_1−x As spherical quantum dot. The calculated energy is computed as a function of Al-concentration. Donor binding energy is found to be quite sensitive to Al-concentration (x), specifically for smallx. Furthermore, the binding energy is found to be highest for the smallest and the center-doped dot indicating the strongest confinement in those cases.     

Dependence of forward deuteron photodisintegration on the D state

The cross section for forward produced protons in deuteron photodisintegration is shown to be moderately sensitive to the % D state of the deuteron. A 4.58% D state model has about half the discrepancy from experiment of a 7.53% model.     

Effects of poly(ethylene glycol) on electrical conductivity of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) film

A series of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) composite thin films with prescribed concentrations of poly(ethylene glycol) were prepared. The PEDOT–PSS pristine film and PEDOT–PSS/PEG films were studied using four-probe method, photoelectron spectroscopy and atomic force microscopy. The electrical conductivity of PEDOT–PSS/PEG hybrid films was found to be enhanced compared to the PEDOT–PSS pristine film, depending on the PEG concentration and molecular weight. XPS analysis and AFM results showed that PEG induces the phase separation between the PEDOT–PSS conducting particles and the excessive PSSNa shell. Simultaneously PEG may form hydrogen bond with sulfonic groups of PSSH, and hence weaken the electrostatic interactions between PEDOT cationic chains and PSS anionic chains. These resulted in the creation of a better conduction pathway among PEDOT–PSS particles, attributed to the improvement of conductivity.