Jaroslav Boháček

Magnetic poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) microspheres by dispersion polymerization

Crosslinked poly(2-hydroxyethyl methacrylate)-based magnetic microspheres were prepared in a simple one-step procedure by dispersion polymerization in the presence of several kinds of iron oxides. Cellulose acetate butyrate and dibenzoyl peroxide were used as steric stabilizer and polymerization initiator, respectively, and ethylene dimethacrylate was a crosslinking agent. The resulting product was characterized in terms of particle size, particle size distribution, iron(III) content, and magnetic properties. In the presence of needle-like maghemite in the polymerization mixture and under suitable conditions, magnetic microspheres with relatively narrow size distribution were formed. An increase in the particle size and, at the same time, a decrease in molecular weight of uncrosslinked polymers resulted, as the continuous phase became richer in 2-methylpropan-1-ol. Coercive force of needle-like maghemite-containing particles was higher than that of cubic magnetite-loaded microspheres. Coercive force increased with the decreasing iron content in the particles.

Thermal analysis methods in the characterization of photocatalytic titania precursors

A new method for the preparation of titania photocatalyst was proposed. Precursors of the photoactive titania were prepared from TiOSO4·nH2O solution by precipitation with ammonia and addition of H2O2 or HNO3, respectively. Methods of TG, DTA, ETA, EGA/MS detection and FTIR were used to characterize the thermal degradation of the titania precursor and to determine the optimal temperature to obtain the photoactive titania. ETA made it possible to characterize the microstructure development of the samples in the heating conditions.

ArF laser photolysis of gaseous CS2–(CH3)4Sn mixtures: gas-phase reaction between tin and sulfur and deposition of nanosized tin sulfides incorporated in a polymer network

ArF laser photolysis of gaseous (CH3)4Sn–CS2 mixtures results in chemical vapour deposition of tin sulfides (SnS and SnS2) incorporated in a network of a blend of polythiene and organotin polymers. The evidence for the tin sulfides was obtained by examination of the deposited coatings by infrared spectroscopy, Raman spectroscopy and electron microscopy. The formation of tin sulfides is explained by reaction of transiently generated Sn and S atoms. The reported results reveal for the first time that nanosized clusters of Sn and S produced in the gas phase react into tin sulfides at ambient temperature of the gas phase.

IR laser-induced thermolysis of (chloromethyl)silane: complex reaction involving H2Si:, H2C: and HClSi: transients and yielding nanostructured Si/C/H phases

Multi-pulse and single-pulse infrared laser induced thermolysis of gaseous (chloromethyl)silane, H3SiCH2Cl occurs via 1,1-HCl and H2C: elimination and dehydrogenation and yields nano-structured Si/C/H phases containing most of the Si and C atoms of the precursor. The identification of final volatile products and observation of H2Si:, H2C: and HClSi: transients by LIF spectroscopy suggest that intermediate silene isomers decompose into silylene and carbene. The deposited films are composed of SiC and polycarbosilane and their H content differs depending on the mode of the IR thermolysis.

Titania aerogels with tailored nano and microstructure: comparison of lyophilization and supercritical drying

Abstract Structure and phase composition of titania aerogels can be substantially influenced simply by the process of drying their parent water colloid suspensions prepared by the reaction of hydrogen peroxide with suspension of precipitates obtained by neutralization of solution of titanyl sulfate with ammonia. Two methods of drying are compared: (1) lyophilization of fast frozen material immersed in liquid nitrogen, and (2) critical point drying using supercritical CO2 under high pressure. Both methods of drying lead to yellow titanium peroxide aerogels consisting of nanometer-sized blocks. While lyophilization leads to foils consisting of nano-sized crystalline nuclei of peroxo-polytitanic acid dispersed in predominantly amorphous material, the critical point drying provides rather bulk highly porous composite consisting of randomly oriented flat nanoparticles (5–10 nm) composed of crystalline anatase and amorphous peroxo-polytitanic acid.