Valeria Gancheva

Kinetic studies on the reaction between copper(II) ions and some dithiocarbonates using stopped-flow technique

Abstract The kinetics of the self-redox reaction of bis(R-dithiocarbonato)copper(II) complexes (R=Me, Et, i -Pr, i -Bu, 2-Bu, Oct) formed in situ by the mixing of water/alcohol solutions of Cu(II) salts and the corresponding alkali salts of the ligands are studied using stopped-flow spectrophotometric technique. It was found that: (i) maximal absorbance at 425 nm due to the studied complex is reached at Cu(II)/ligand ratio=1:2; (ii) reduction of Cu(II) to Cu(I) follows the kinetics of a second-order reaction in respect to the bis-chelate; (iii) the measured rate constants decrease with increasing the size of the remote ligand substituents; (iv) the rate constant depends on the type and the concentration of the alcohol in the solvent. The obtained results are discussed in terms of a self-redox reaction between Cu(II) and thiols proceeding within the associate between two bis(R-dithiocarbonato)copper(II) molecules without the formation of free radicals from the ligands.

Complex Formation Between Lysozyme and Stabilized Micelles with a Mixed Poly(ethylene oxide)/Poly(acrylic acid) Shell

The electrostatic complexation between lysozyme and stabilized polymeric micelles (SPMs) with a poly(acrylic acid) (PAA) or a mixed poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) shell (SPMs with a mixed shell, SPMMS) and a temperature-responsive poly(propylene oxide) (PPO) core was investigated by means of dynamic, static, and electrophoretic light scattering. The SPMs and different types of SPMMS used resulted from the self-assembly of PAA-PPO-PAA triblock copolymer chains, or PAA-PPO-PAA and PEO-PPO-PEO triblock copolymer chain mixtures (with varying chain lengths and molar ratios) in aqueous solutions at pH 10 and the subsequent cross-linking of their PPO cores via loading and photo-cross-linking of pentaerythritol tetraacrylate (PETA). The solution behavior, structure and properties of the formed complexes at pH 7 and 0.01 M ionic strength, were studied as a function of the protein concentration in the solution (the concentration of the stabilized micelles was kept constant) or equivalently the ratio of the two components. The complexation process and properties of the complexes proved to be dependent on the protein concentration, while of particular interest was the effect of the structure of the shell of the SPMs on the stability/solubility of the complexes. Finally, the fluorescence and mid infrared spectroscopic investigation of the structure of the complexed protein showed that, although a small stretching of the protein molecules occurred in some cases, no protein denaturation takes place upon complexation.

Transparent back contacts for P3HT:PCBM bulk heterojunction solar cells

A new combination of layers functioning as a transparent contact is proposed and tested in real solar cells. The contacts consist of TiO2 layers and thin metal layers (Ag, Cu) and are deposited by magnetron sputtering. The optical transmission and electrical conductivity of the transparent contact layers (TCL) are measured. The TCLs are applied as back contacts in bulk heterojunction polymer solar cells deposited on ITO covered glass and consisting of the following layers: ITO/PEDOT:PSS/P3HT:PCBM/back contact. The organic layers are deposited by spin-coating. For comparison, the same bulk heterojunction polymer solar cells are prepared with a sputtered Ag back contact. The first results show a dependence of the current-voltage parameters of the studied solar cells on the thickness of the different component layers of the transparent back contacts. There is a balance that has to be observed between the electrical characteristics of the contacts and their optical transparency. Future plans involve their inclusion as intermediate contacts in tandem organic solar cells.

Optical, film surface and photovoltaic properties of PTB7-Fx-based polymer-organic solar cells prepared in ambient conditions

Bulk heterojunction organic solar cells based on active layer of PTB7-Fx (x = 0–100), conjugated block copolymer incorporating benzo[1,2-b:4,5-b′]dithiophene and partly fluorinated thieno[3,4-b]thiophene units, and fullerene derivatives as phenyl C61 and phenyl C71 butyric acid methyl esters sandwiched between a transparent anode of indium tin oxide, a hole conducting layer of either poly(ethylene dioxythiophene) : polystyrene sulfonate or magnetron-sputtered molybdenum oxide and evaporated aluminum cathodes were fabricated. Polymer-organic thin films were prepared at 1:1.5 mass ratio of the donor:acceptor mixture and deposited from dichlorobenzene solution of different concentrations by spin coating in ambient conditions. To control the active layer morphology, the films were subjected either to post-deposition treatments (annealing) at different temperatures or incorporation of an additive such as diiodooctane. Optical transmission, film surface topography and thickness measurements were used to characterize the active layer. Test devices with the architecture described above were prepared and their current–voltage characteristics, quantum efficiency and impedance spectra were measured and used to compare the different active layers, architectures and deposition sequences.

Performance and stability of two types of bulk heterojunction polymer solar cells with sputtered back contacts

Two types of polymer solar cells with active layers of P3HT:PCBM and PCDTBT:PCBM in a standard configuration were deposited by spin-coating the polymer layers and sputtering the Ag back contacts. After encapsulation, they were subjected to post-deposition annealing and were studied by measuring their current-voltage characteristics and quantum efficiency spectra. Their stability was examined by exposing them to solar radiation in open-circuit conditions for several hours every day for a total of 80 hours. Their characteristics were measured regularly throughout this period. The performance of the two types of cells are compared and discussed.

Synthesis and Properties of Amphiphilic and Functional Copolymers and Networks

Well-defined amphiphilic and functional copolymers and networks based on cyclic ethers, oxazolines and aziridines were prepared. The synthesis of copolymers with controlled hydrophilic-hydrophobic balance, composition and structure was achieved using sequential living cationic polymerization, copolymerization of macromonomers, functionalization of conventional polymers and following grafting or crosslinking by telechelic polymers. Properties, displaying the amphiphilic nature of the copolymers were examined: solubility, swelling in water and hydrocarbons. Anion-exchange and sorption capacity towards metal ions of the copolymers bearing quatemary ammonium groups were evaluated. Environmentally responsive conformational changes, aggregation and microphase separation were observed for some of the products.