N. N. Shevchenko

Polarization-dependent suppression of Bragg reflections in light reflection from photonic crystals

This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ϑc, at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ϑc, which depends on the geometric parameters and dielectric constants of the spatially periodic structure.

Sorption of vapors of aromatic compounds by cross-linked polymer particles containing luminophores: A spectroscopic study

Monodispersed core-shell particles 290–315 nm in diameter were prepared by seed emulsion copolymerization of styrene with divinylbenzene in the presence of luminophore-containing comonomers. The capability of the particles obtained to sorb toluene vapor was shown by solid-state 1H and 13C NMR spectroscopy.

Copolymerization of styrene with N-vinylformamide and ethylene glycol dimethacrylate and characteristics of the formed particles

Emulsion and emulsifier-free emulsion polymerization of styrene, N-vinylformamide, and ethylene glycol dimethacrylate are investigated with the goal to form positively charged monodisperse submicron crosslinked particles. The effects of the monomer ratio, the type and concentration of the buffer salt, and the emulsifier concentration on the monomer conversion and on the shapes, size distributions, and surface characteristics of the formed particles are studied. It is shown that, in the surface layers, amino groups prevail over carboxylic groups. The total surface concentration of acidic and basic groups increases with the degree of crosslinking of particles and as a result of their subsequent surface hydrolysis.

Bioligand carriers based on methyl methacrylate copolymers with N-vinylformamide or glycidyl methacrylate

Emulsifier-free emulsion copolymerization of methyl methacrylate with N-vinylformamide and glycidyl methacrylate initiated by a cationic or anionic azoinitiator in the presence of dextran is used to produce monodisperse polymer particles with a developed multifunctional surface. As a result, monodisperse particles are obtained with a diameter of 350–660 nm, the surface layer of which contains, in addition to carboxyl groups, amino or epoxy groups. The conditions are determined for the formation of multifunctional hydrophilic particle surface via the hydrolysis of comonomer units and residual groups of initiators. The limiting values of bovine serum albumin chemisorption (2.4 and 1.0 mg/m2 on the particles of methyl methacrylate copolymers with glycidyl methacrylate or N-vinyl formamide, respectively) indicate that the obtained particles have sufficient sorption capacity to be applied as carriers for immunoreagents.

Crosslinked monodisperse particles containing luminophore groups in shells for molecular recognition of lower alcohols

The molecular imprinting technique is used for the synthesis of monodisperse polymer particles via the seed emulsion copolymerization of methyl methacrylate, ethylene glycol dimethacrylate, and comonomers based on Nile Red. The introduction of lower alcohol templates into the reaction mixture and their removal after the synthesis lead to the formation of molecular-recognition sites in the shell that contain luminophore groups and give an optical response to the presence of methanol and ethanol in the gas phase. The particles are investigated via electron microscopy and dynamic light scattering, and their specific surface area is determined through the BET method. The kinetics of a change in the luminescence of thin films based on the particles in vapors of lower alcohols is investigated.

Direct opal-like structures consisting of monodisperse polymer particles and synthesis of the related inverse structures

Three-dimensional periodic solid-state film structures with a face-centered cubic lattice and a high degree of perfection have been prepared from monodisperse particles of styrene copolymers with methacrylic acid. It has been shown that these structures can be successfully used not only as model objects for studying specific features of light propagation in photonic crystals but also as templates for synthesizing inverse opal-like structures. The influence of the degree of hydrophilization of the surface layer of polymer particles forming a polymer template and the template synthesis conditions on the quality of an inverse opal-like TiO2-based structure has been analyzed.

Luminophore-containing polymer particles: Synthesis and optical properties of thin films on their basis

For the synthesis of monodisperse submicron particles (in which a luminophore is covalently bound to the polymer matrix), methods of emulsifier-free emulsion and seeded copolymerizations are applied to introduce the luminophore-containing monomer into the bulk or shell of the particles, respectively. Scanning electron microscopy and optical spectroscopy (reflection and luminescence spectra) showed that the particles obtained by the first method are better able to self-assemble into 3D-ordered thin-film structures displaying photonic crystalline properties.

Cross-linked poly(methyl methacrylate) particles with surface amino groups

Positively charged monodisperse particles have been synthesized via emulsifier-free emulsion copolymerization of methyl methacrylate with vinylformamide and ethylene glycol dimethacrylate. The effect of the cross-linking agent on the conversion of the monomers, as well as on the shape, size distribution, and surface characteristics of the obtained particles, has been determined. Addition of the cross-linking agent (5 wt %) to the reaction system has been shown to result in the formation of particles, which, after hydrolysis, have positive ζ potentials at pH 2–10.

Monodisperse polymer particles with molecular imprints of naphthalene in the shell: Synthesis and adsorption properties

Methods of seed heterophase polymerization of ethylene glycol dimethacrylate and its copolymerization with styrene or trimethylolpropane trimethacrylate with the aim to prepare monodisperse cross-linked core-shell particles were studied. The possibilities of molecular imprinting for forming sites for molecular recognition of naphthalene molecules were examined. The adsorption ability of the particles obtained is influenced by the naphthalene concentration and porogenic solvent polarity in the polymerization mixture.

Self-assembly of ensembles of polystyrene submicroparticles modified by styryl dye in evaporating microdrop of solution

The dependence that the morphology of the ensemble of polystyrene particles deposited on a glass carrier from an evaporating drop of colloidal solution has on the presence of styryl dye chemically sorbed on their surface was studied. It was shown that, in the presence of the dye, a solid phase is formed which covers the carrier more uniformly but with a less expressed long-range order of particles.