Alexander V. Chernyak

A strong influence of the positions of solubilizing alkyl side chains on optoelectronic and photovoltaic properties of TTBTBTT-based conjugated polymers

We report the synthesis and comparative study of five conjugated polymers P1–P5 with different arrangements of two solubilizing 2-ethylhexyl side chains in their repeating units. It has been shown that positioning of the alkyl substituents affects strongly frontier energy levels of the polymers and results in variation of their optical band gaps between 1.65 and 2.0 eV. The highest (2.8 × 10−4 cm2 V−1 s−1) and the lowest (2.4 × 10−5 cm2 V−1 s−1) charge carrier mobilities determined for the polymers P1 and P5, respectively, using a SCLC technique differ by more than one order of magnitude. GIWAXS measurements also revealed very different degrees of molecular ordering in the films of polymers P1–P5 which correlate well with the SCLC mobility data and solid state photoluminescence spectra of these materials. The bulk heterojunction solar cells based on the composites of polymers P1–P5 with [60]PCBM demonstrated power conversion efficiencies ranging from 0.6% (P5) to 5.1% (P1) thus evidencing a strong influence of the alkyl side chains on the photovoltaic performance of the designed polymer-based materials.

Mobility of protons in 12-phosphotungstic acid and its acid and neutral salts

The proton mobility in 12-phosphotungstic heteropolyacid (PWA) and its salts (Cs2HPW12O40·xH2O, Cs3PW12O40·xH2O, (NH4)3PW12O40·xH2O) was investigated by impedance spectroscopy and nuclear magnetic resonance with pulsed field gradient under wide range of relative humidity. Values of two diffusion components observed in PWA as well as in its acid cesium salt differ in one order of magnitude. Also there are two components in the impedance spectra of these compounds. Thus, we suggest, the proton transport take place both inside the grains and along its boundaries. Self-diffusion coefficients, observed in the neutral cesium and ammonium salts, are close to each other and equal to the fast diffusion coefficient in acid cesium salt. At the same time, there is the only relaxation component in the impedance spectra of neutral salts. Thus, it can be concluded, that in case of neutral salts of PWA, there is no proton transport inside the grains of these compounds, and their high proton conductivity caused by fast proton transport along the grain boundaries.

New polymer electrolytes based on polyethylene glycol diacrylate–LiBF4–1-ethyl-3-methylimidazolium tetrafluoroborate with the introduction of alkylene carbonates

Polymer gel electrolytes based on polyethylene glycol diacrylate (PEG DA), salt LiBF4, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) were synthesized and studied in the presence of propylene carbonate and ethylene carbonate as solvents. The mechanism of ionic transport in the system was studied using electrochemical impedance spectroscopy, liquid mass spectrometry, pulse-field-gradient spin echo NMR spectroscopy. The range of operating temperatures of the gel electrolytes was determined by DSC. The total conductivity at room temperature in these systems is about 10–3 S cm–1. The self-diffusion coefficients on 7Li nuclei in the systems with a solvent attain the values about 10–10 m2 s–1, and in the PEG DA–LiBF4–EMIBF4 system they range from 10–13 to 10–12 m2 s–1. Ternary associates [(EMI)2(BF4)]+ and [Li+(BF4)2]– were found by liquid mass spectrometry to be the main charge carriers.

Nanocomposite network polymer gel-electrolytes: TiO2- and Li2TiO3-nanoparticle effects on their structure and properties

The effects of TiO2-(∼60 nm) and Li2TiO3-(∼20 nm) nanoparticles on the conductivity, structure, and mechanical strength of (polyether diacrylate-LiClO4-ethylene carbonate)-based polymer gelelectrolytes are studied. When the gel-electrolytes are synthesized with the TiO2- and Li2TiO3-nanoparticles ultrasonic pretreatment, both polyether diacrylate and ethylene carbonate are partially decomposed in the solution; this is evidenced by the appearance of -CH3-group signal at 1.2 ppm in 1H-NMR-spectra, as well, as by the peak area analysis. The gel-electrolyte matrix partial decomposition was shown not to affect the network polymer electrolyte conductivity and mechanical properties. Analysis of NMR spectra for 7Li nuclei, taken with nanocomposite polymer electrolyte rotating under magic angle, revealed two Li+ ion environments: with the nanoparticles and the polymer matrix. Upon the adding of TiO2 nanoparticles (10 mass %) the polymer electrolyte conductivity increased by order of magnitude (up to 1.8 × 10−3 S/cm at 20°C); upon the adding of Li2TiO3, by a factor of 2 only (up to 7.0 × 10−4 S/cm at 20°C). The electrolyte-solution ultrasonic treatment increased the films’ mechanical strength; the larger effect occurred with Li2TiO3 (the modulus of elasticity is 15 MPa).

Solvation environment of lithium ion in a LiBF4–propylene carbonate system in the presence of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid studied by NMR and quantum chemical modeling

Solutions of lithium and 1-ethyl-3-methylimidazolium tetrafluoroborates ([emim][BF4]) in propylene carbonate (PC) were studied by the high-resolution NMR method on 1H, 7Li, 11B, 13C, and 19F nuclei. The degree of solvation of lithium ions was determined by measuring selfdiffusion coefficients by pulse-field-gradient spin echo NMR method on 1H, 7Li, and 19F nuclei. The hydrodynamic radii of solvated Li+ cations were estimated by the Stokes–Einstein equation. The model structures of the solvation complexes of Li+ ion with propylene carbonate molecules and BF4– anion and their associates with ionic liquid components were calculated in terms of the density function theory. The calculated values of the chemical shifts were compared with the experimental data. PC molecules were predominantly bound to the Li+ cation, while LiBF4–[emim][BF4]–PC (1: 4: 4) electrolyte had a maximum conductivity of 9.5 mS cm–1 at 24 °С compared to the compositions of a lower content of the solvent.

NMR study of the polyethylene glycol diacrylate-LiBF4-1-butyl-3-methylimidazolium tetrafluoroborate-propylene/ethylene carbonate electrolyte system

The 1-butyl-3-methylimidazolium tetrafluoroborate-propylene carbonate-ethylene carbonate system in a reticular polymer electrolyte based on polyethylene glycol diacrylate and LiBF4 was studied by high-resolution and pulsed field gradient NMR. The 1H, 13C, 7Li, and 19F NMR spectra of the electrolyte systems were analyzed. During the electrolyte synthesis, propylene undergoes structural changes in the ionic liquid, which adversely affects the ion conductivity (the maximum conductivity in this system is 8.46 × 10−4 S/cm at 20°C) and the self-diffusion coefficients of the lithium ions. When the propylene carbonate content in the polymer electrolyte increased from 15 to 32 wt %, the proportion of lithium ions with a high self-diffusion coefficient (10−11 m2/s) decreased from 24 to 7%. In the case of ethylene carbonate, this effect was less pronounced, the conductivity in these systems reaching 2.46 × 10−3 S/cm at 20°C. The high-resolution NMR study did not reveal any structural changes in the ionic liquid and ethylene carbonate during the modeling of radical polymerization.

Influence of the reticular polymeric gel—electrolyte structure on ionic and molecular mobility of an electrolyte system salt—ionic liquid: LiBF4—1-ethyl-3-methylimidazolium tetrafluoroborate

Peculiarities of the formation of a reticular polymeric gel—electrolyte matrix based on polyethylene glycol diacrylate in a medium of ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) were studied by isothermal calorimetry. The influence of the polymeric matrix structure on the ionic and molecular mobility of a LiBF4 salt—ionic liquid electrolyte system was considered. The self-diffusion coefficients on the 1H, 7Li, and 19F nuclei were measured by pulsed field gradient NMR. For the all electrolyte compositions, the highest translation mobility of the cationic part of the EMI+ ionic liquid molecule is observed on 1H nuclei, whereas the lowest one corresponds to 7Li nuclei. This phenomena is due to the strong association of the lithium salt in a polar medium of the ionic liquid, which is concentrated in cavities of the reticular polymer.

Hydrolysis of isobutylaluminum aryloxides studied by 1H NMR and quantum chemical methods

AbstractThe results of 1H NMR and quantum chemical studies of hydrolysis of isobutylaluminum aryloxides are presented. According to the data of 1H NMR spectroscopy, the hydrolysis of monomeric diisobutylaluminum aryloxides (2,6-Bu2t—C6H3O)AlBu2i and (2,6-Bu2t,4-Me—C6H2O)AlBu2i occurs selectively at the Al—OAr bond to form the corresponding sterically bulky phenol and polyisobutylaluminoxane. At the molar ratios Al: H2O = 2, the formed sterically bulky phenol reacts slowly with diisobutylaluminum monoaryloxide to form isobutylaluminum diaryloxide. Dimeric aryloxide [(2-But—C6H4O)AlBu2i]2 is not hydrolyzed under similar conditions. The quantum chemical calculations confirmed the experimental results: the hydrolysis at the Al—OAr bond has a lower energy barrier than that at the Al—C bond because of the formation of

Quantum chemical modeling of the degradation of the polymer matrix and solvent molecules in nanocomposite polymer gel electrolytes

{H_{{H_2}O}} \ldots {O_{O - Ar}}