A. Yu. Nikolaev

Formation of superhydrophobic surfaces by the deposition of coatings from supercritical carbon dioxide

The deposition of uniform coatings of fluorinated polymers from solutions in supercritical carbon dioxide on a number of rough substrates allowed superhydrophobic (ultrahydrophobic) properties to be imparted to their surfaces, and, namely, to increase the value of the contact angle for water droplet to 150° and greater. The dynamics of changing of geometry of a drying droplet on a substrate is studied. A procedure is developed that permits the penetration of water into the substrate to be detected.

Design and synthesis of new ultra-low band gap thiadiazoloquinoxaline-based polymers for near-infrared organic photovoltaic application

Two D–A copolymers, F1 and F2, with fluorene and thiazole units were substituted, respectively, on a thiadiazoloquinoxaline (TDQ) unit to enhance the electron-accepting strength of TDQ. The copolymers were synthesized by a cross-coupling Stille reaction and their optical and electrochemical properties were examined, which revealed that they have ultra-low band gaps and absorption in the near-infrared. These copolymers were employed as donors along with PC71BM as an electron acceptor for the fabrication of solution-processed bulk heterojunction (BHJ) polymer solar cells. After the optimization of the donor-to-acceptor weight ratio and the solvent additive (4 v% DIO as solvent additive), devices with F1:PC71BM and F2:PC71BM displayed power conversion efficiencies (PCEs) of 5.80% and 3.32%, respectively. Although F2 possesses a broader absorption profile compared with F1, the lower value of PCE for the F2-based device was attributed to the low LUMO offset between F2 and PC71BM, which limited the exciton dissociation. The abovementioned results indicate that these copolymers can be utilized for ternary BHJ and tandem solar cells to achieve a high PCE.

Effect of supercritical carbon dioxide on nanoporous polyhexafluoropropylene

The effect of supercritical CO2 (sc-CO2) on the size distribution of free volume holes (nanopores) in a polyhexafluoropropylene (PHFP) polymer matrix has been studied. Residual (after CO2 release) swelling improves gas transport properties of the material. Relaxation of these properties over time has been compared with changes in permeability and nanoporosity. For PHFP samples with different histories, the data on nanoporosity have been obtained using positron annihilation lifetime spectroscopy (micropores) and the lowtemperature gas sorption technique (mesopores and part of micropores). Matching of the data is intended to reveal the role of pores of different sizes in permeability of membrane materials to different gases and determine the specifics of application of the positron annihilation technique to studying sc-CO2-modified objects.

Categorization system of nanofillers to polymer composites

The paper deals with a systematic categorization of nanofillers in terms of their effect arising upon introduction into polymer composites of tribological applications. The authors study the nature of this effect and the tribological behavior of different types of nanofillers acting in composites and exhibiting either a tribochemical effect or a discrete surface one. Nanofillers having an indirect influence on friction and intercalation compounds are also studied.

Electrocatalysts for fuel cells synthesized in supercritical carbon dioxide

We applied the method of directly depositing an organometallic precursor from a solution in supercritical carbon dioxide on a dispersed carbon substrate surface followed by reduction to obtain a number of electrocatalytic materials in the form of nanoscale platinum particles on dispersed carbon supports (Vulcan XC72r carbon black, acetylene black, nanotubes). The synthesized materials persistently showed a monodisperse size distribution of platinum particles with an average diameter of 2–3 nm, regardless of the substrate nature, and a uniform distribution over the support surface. The synthesized electrocatalysts (ECs) were tested as part of an operating cathode electrode of a phosphoric acid fuel cell (FC) with a PBI matrix. In this case, the membrane-electrode assembly with this cathode showed current-voltage characteristics as good as the reference characteristics achieved with electrodes produced by BASF.

Structure of composites prepared via polypyrrole synthesis in supercritical CO2 on microporous polyethylene

The synthesis of polypyrrole in supercritical carbon dioxide in the presence of the microporous polyethylene has been studied. Formation of polymer composites based on polypyrrole and polyethylene has been demonstrated. The structure of the test samples has been investigated by vibrational spectroscopy, SAXS, and atomic force and scanning electron microscopy. It has been discovered that the oxidized structure of polypyrrole forms during the synthesis under supercritical conditions.

Specific features of the copolymerization of acrylonitrile and acrylamide in the presence of low-molecular-mass and polymeric trithiocarbonates and properties of the obtained copolymers

Regularities of the formation of acrylonitrile-acrylamide copolymers obtained from initial monomer feeds containing 1–50 wt % acrylamide in DMSO solutions with the participation of low-molecular-mass and polymeric trithiocarbonates as reversible addition-fragmentation chain transfer agents are studied for the first time. It is shown that the copolymerization in the presence of low-molecular-mass trithiocarbonates proceeds via a pseudo-living mechanism. The synthesized copolymers prove to be inefficient as reversible addition-fragmentation chain transfer agents, a result that leads to products with bimodal molecular-mass distributions. The rheological characteristics of solutions, as well as the thermal behavior of the copolymers obtained in the absence and in the presence of reversible addition-fragmentation chain transfer agents, are studied. The effect of the synthesis conditions on the properties of the synthesized copolymers is discussed.

Effects of synthesis conditions and the mechanism of homopolymerization of acrylonitrile on the thermal behavior of the resulting polymer

The effect of the conditions of polyacrylonitrile synthesis (nature of the solvent, homogeneity of the reaction medium, and type of initiation) on the conditions of formation of the polyconjugation system during the pyrolysis of polyacrylonitrile is studied. The controlled synthesis of polyacrylonitrile via radiation polymerization mediated by dibenzyl trithiocarbonate as a reversible addition-fragmentation chain-transfer agent at 25 and 80°C is performed for the first time. It is shown that the type of initiation in reversible addition-fragmentation chain-transfer polymerization (material initiation or radiolysis) strongly affects the structure of the formed polyconjugation system.

Synthesis and photophysical properties of regioregular low bandgap copolymers with controlled 5-fluorobenzotriazole orientation for photovoltaic application

Two copolymers P1 and P2, with regioregular and random structures, respectively, were synthesized and their optical and electrochemical properties (both theoretical and experimental) were investigated. The regioregular copolymer P1 showed a lower optical bandgap and a high degree of crystallinity compared to the random P2 copolymer. These copolymers were used as electron donors along with PC71BM as the electron acceptor for the fabrication of solution processed bulk heterojunction solar cells. After the optimization of the weight ratio between the donor and the acceptor and the concentration of the solvent additive i.e. DIO in chloroform, the solar cells based on regioregular P1 exhibit higher power conversion efficiency (7.66%) than the random P2 (5.33%). The enhancement in the power conversion efficiency has been attributed to the increased hole mobility due to the high regioregularity of the conjugated copolymer backbone and effective ordering between the polymer chains. This work brings forth and establishes the importance of copolymers having a regioregular A–D–A–D structure so as to offer significant performance benefits over the random D–A copolymer. This approach is a promising new route to materials for highly efficient polymer solar cells.

Homo- and copolymers of acrylonitrile: Effect of the reaction medium on the thermal behavior in an inert atmosphere

The effects of the synthesis conditions of acrylonitrile homo- and copolymers—such as the type of solvent, the homogeneity of the reaction medium, the type, and the amount of comonomer—on the conditions of formation and the structure of the polyconjugation system during pyrolysis of the synthesized polymers under an inert atmosphere are studied. In all experiments, the total concentration of the monomers, the concentration of initiator, the temperature of polymerization, and the conversion of the monomers remain constant.