Yu. V. Kulvelis

Effect of the Cu content and ZnS treatment on the characteristics of synthesized ZnS:(Cu, Cl) electroluminescent phosphors

The effect of the pretreatment of ZnS via different methods on the characteristics of synthesized ZnS:(Cu, Cl) electroluminescent phosphors with varying concentrations of the activator dopant (Cu) is studied. As a result of the pretreatment of ZnS with accelerated electrons and in nitrogen plasma, an increase in the emission brightness of the synthesized phosphor and a shift of the luminescence spectrum to longer wavelengths are observed. These effects are attributed with increase in content of the activator in the phosphor matrix because of the formation of extra defects in the ZnS structure during treatment. In the case of shockwave treatment of ZnS, the generation of defects is not compensated by heat treatment during synthesis of the phosphor, and a positive enhanced-brightness effect is not attained.

Scientific principles of a new process for manufacturing perfluorinated polymer electrolytes for fuel cells

A new process for manufacturing a perfluorinated polymer electrolyte for proton-conducting membranes of fuel cells is presented. The process is based on the aqueous emulsion copolymerization of tetrafluoroethylene (TFE) with perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonyl fluoride (FS-141) and characterized by a high productivity, reduced consumption of the expensive sulfonated monomer, and the possibility of controlling the equivalent weight (EW) of the resulting copolymer. The copolymers are characterized by a uniform composition in combination with optimal EW values and afford the synthesis of proton conducting membranes for fuel cells with properties comparable with those of commercial Nafion membranes. A mechanism of the copolymerization of TFE with FS-141 in an aqueous emulsion is proposed and confirmed by kinetic and topochemical data.

Synthesis and structural investigation of ferrofluids with porphyrins and prospects of their application in photodynamic therapy

Complexes of superparamagnetic nanoparticles of magnetite with porphyrins, i.e., sulfonated tetraphenylporphine dihydrochloride (H2TPPS4(HCl)2) and photodithazine (used in photodynamic therapy for treatment of oncological diseases), in an aqueous medium have been synthesized for the first time and investigated using small-angle neutron scattering and spectrophotometry. The influence of the biocompatible polymer Pluronic on the functional properties of the synthesized complexes has also been analyzed. It has been shown that the synthesized complexes of ferrofluids with photodithazine and Pluronic exhibit a high efficiency as compounds capable of suppressing the reproduction of tumor cell cultures. The results obtained can be used in the design of a magnetically guided drug for photodynamic therapy.

Structure characterization of perfluorosulfonic short side chain polymer membranes

Small-angle neutron scattering has been used to study the structure of dry and wet perfluorinated short side chain membranes first synthesized by a new aqueous emulsion method. These membranes are new prospective materials for hydrogen fuel cells and have advantages over long side chain Nafion-type membranes. Experiments enabled us to recognize the subtle features of the membrane structure being responsible for the proton conductivity. The parameters of pores interconnected and forming the channels for diffusion of water molecules and protons were determined as dependent on the chemical composition of the membranes. It was discovered that there was an influence of molecular weight and equivalent weight, varied during synthesis, on the polymer structure.

Structure and property optimization of perfluorinated short side chain membranes for hydrogen fuel cells using orientational stretching

Small-angle neutron scattering has been applied to study the structure peculiarities of perfluorinated proton conducting polymer samples containing sulfonic groups of the Aquivion® type in dry and moistened conditions, which differ from Nafion® type membranes by the length of the side chains with sulfonic acid groups. The fine structure of the membranes is revealed, which is based on a system of regular proton conducting channels in the perfluorinated polymer matrix. The way this fine structure changes was determined as a function of the equivalent weight of the membrane, and the relation of these changes with proton conductivity value is established. The neutron contrast variation method enabled us to study the effect of orientational stretching on the fine structure. It was found that stretching is accompanied by an increase in proton conductivity due to changes in the fine structure of the channel system. Our investigations confirm that a reduction in the side chain length affects the fine structure of the perfluorinated proton conducting membranes, which is accompanied by an improvement in their performance in hydrogen fuel cells. Therefore, Aquivion® type systems will allow to reduce and possibly remove the existing operational restrictions of Nafion®.

Small-angle neutron scattering from polymer hydrogels with memory effect for medicine immobilization

Hydrogels synthesized based on cross-linked copolymers of 2-hydroxyethyl methacrylate and functional monomers (acrylic acid or dimethylaminoethyl methacrylate), having a memory effect with respect to target medicine (cefazolin), have been investigated by small-angle neutron scattering. The hydrogels are found to have a two-level structural organization: large (up to 100 nm) aggregates filled with network cells (4–7 nm in size). The structural differences in the anionic, cationic, and amphiphilic hydrogels and the relationship between their structure and the ability of hydrogels to absorb moisture are shown. A relationship between the memory effect during cefazolin immobilization and the internal structure of hydrogels, depending on their composition and type of functional groups, is established.

Structure of magnetically guided nanocarriers of the photodithazine sensitizer from small-angle neutron scattering data

Nanosized complexes of ferromagnetic particles with a photodithazine sensitizer (used in photo-dynamic therapy in oncology) have been synthesized and investigated using small-angle neutron scattering for the first time. The structure of the complexes has been determined, and the influence of the biocompatible polymer Pluronic on their structure has been analyzed. The possibilities of using the complexes for magnetically guided delivery of the photosensitizer to cells and tissues in the treatment of oncological diseases by photodynamic therapy have been discussed.

Complexes of poly-N-vinylpyrrolidone with sulfonated tetraphenylporphins

The interaction of sulfonated tetraphenylporphins H2TPPS4(HCl)2 and in CuTPPS4 with poly-N-vinylpyrrolidone (PVP) is studied using small-angle neutron scattering, dynamic light scattering, visible spectrophotometry, and viscometry. It is shown that porphyrin molecules form complexes with PVP, thus charging the polymeric chain.

Dynamics of water in binary and ternary solutions of DNA and porphyrins

The dynamics of heavy water (at 20°C) in solutions with polyanionic DNA chains and ternary systems containing DNA and negatively charged tetraphenylporphyrins has been investigated using neutron resonance spin echo in the time range t = 1−1000 ps. The diffusion dynamics has been observed in the momentum transfer range q = 1.3−1.8 Å−1, and the relaxation rates in single-component, binary, and ternary systems are close to each other. Apart from the relaxation, the vibrational mode in the solutions has been revealed at the momentum transfer q = 1.9 Å−1. The introduction of porphyrins into the solution (one molecule per ten DNA base pairs) has resulted in a retardation of diffusion and a considerable increase (by 5–10%) in the frequency of translational vibrations of water molecules due to the interaction with porphyrin molecules.