Michal Machovsky

Novel synthesis of core–shell urchin-like ZnO coated carbonyl iron microparticles and their magnetorheological activity

The overall stability (thermo-oxidation, sedimentation) of MR suspensions is a crucial problem decreasing their potential applicability in real life. In this study the unique functional coating of carbonyl iron (CI) particles with ZnO structures was presented in order to develop a new MR suspension based on the core–shell ZnO/CI urchin-like dispersed particles. The two-step synthesis provides the suitable core–shell particles with improved sedimentation and also thermo-oxidation stability. Moreover, due to the enhanced sedimentation stability core–shell based suspensions exhibit higher values of the yield stress than those of bare CI based suspensions at 20 wt% particle concentration. The suspension with 60 wt% particle concentration reaches values of the yield stress around 2.2 kPa at 272 mT. The excellent MR efficiency of the core–shell ZnO/CI based suspension at elevated temperatures was observed. Finally, the dimorphic particle based suspension was prepared when the ratio between the carbonyl iron and core–shell urchin-like particles was 1 : 1. The highest yield stress was obtained in the case of a dimorphic particle-based suspension due to the good magnetic properties of the bare carbonyl iron and mechanical gripping between core–shell ZnO/CI urchin-like particles.

The formation mechanism of iron oxide nanoparticles within the microwave-assisted solvothermal synthesis and its correlation with the structural and magnetic properties

Magnetic nanoparticles based on Fe3O4 were prepared by a facile and rapid one-pot solvothermal synthesis using FeCl3·6H2O as a source of iron ions, ethylene glycol as a solvent and NH4Ac, (NH4)2CO3, NH4HCO3 or aqueous NH3 as precipitating and nucleating agents. In contrast to previous reports we reduce the synthesis time to 30 minutes using a pressurized microwave reactor without the requirement of further post-treatments such as calcination. Dramatically reduced synthesis time prevents particle growth via Ostwald ripening thus the obtained particles have dimensions in the range of 20 to 130 nm, they are uniform in shape and exhibit magnetic properties with saturation magnetization ranging from 8 to 76 emu g(-1). The suggested method allows simple particle size and crystallinity tuning resulting in improved magnetic properties by changing the synthesis parameters, i.e. temperature and nucleating agents. Moreover, efficiency of conversion of raw material into the product is almost 100%.

Antibacterial performance of ZnO-based fillers with mesoscale structured morphology in model medical PVC composites

Three different ZnO-based antibacterial fillers having different morphologies in microscale region were prepared by the use of the microwave assisted synthesis protocol created in our laboratory with additional annealing in one case. Further, PVC composites containing 0.5-5 wt.% of ZnO based antibacterial fillers were prepared by melt mixing and characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Mechanical testing showed no adverse effect on the working of polymer composites due to either of the fillers used or the applied processing conditions in comparison with the neat medical grade PVC. The surface antibacterial activity of the compounded PVC composites was assessed against Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 6538P according to ISO 22196: 2007 (E). All materials at almost all filler loading levels were efficient against both species of bacteria. The material with the most expanding morphology assuring the largest contact between filler and matrix achieved an excellent level of more than 99.9999% reduction of viable cells of E. coli in comparison to untreated PVC and performed very well against S. aureus, too. A correlation between the morphology and efficacy of the filler was observed and, as a result, a general rule was formulated which links the proneness of the microparticles to perform well against bacteria to their shape and morphology.

Preparation of microfibers from wood/ionic liquid solutions

Two types of ionic liquids, 1-ethyl-3-methylimidazolim acetate and 1-ethyl-3-methylimidazolium lactate, were employed for the direct processing of pine wood into microfibers. The concentration of 5 wt.% of wood in ionic liquids was rated as the most appropriate for electrospinning. The fibers were electrospun into the collector water bath. The final structure varied from individual microfibers to fiber bundles. It was demonstrated that 1-ethyl-3-methylimidazolium lactate is a powerful solvent and provides the direct transformation of pristine pine wood into the non-wovens.

Hybrid nanostructured Ag/ZnO decorated powder cellulose fillers for medical plastics with enhanced surface antibacterial activity

Hybrid inorganic–organic fillers based on nanostructured silver/zinc oxide decorations on micro-cellulose carrier particles were prepared by stepwise microwave assisted hydrothermal synthesis using soluble salts as precursors of silver and zinc oxide. Hexamethylenetetramine was used as precipitating agent for zinc oxide and reducing agent for silver. The inorganics covered all available surfaces of the cellulose particles with a morphology resembling a coral reef. Prepared particulate fillers were compounded to medical grade poly(vinyl chloride) matrix. Scanning electron microscopy and powder X-ray diffractometry were used to investigate the morphology and crystalline phase structure of fillers. The scanning electron microscopy was used for morphological study of composites. With respect to prospective application, the composites were tested on electrical and antibacterial properties. A small effect of water absorption in polymer composites on their dielectric properties was observed but no adverse effect of water exposure on prepared materials was manifested. Electrical conductivity of fillers and composites was measured and no influence of water soaking of composites was found at all. The surface antibacterial activity of prepared composites was evaluated according to the standard ISO 22196. Excellent performance against Escherichia coli and very high against Staphylococcus aureus was achieved.

Antimicrobial Silver Nitrate-doped Polyvinyl Chloride Cast Films: Influence of Solvent on Morphology and Mechanical Properties

Medical-grade polyvinyl chloride was modified by incorporation of silver nitrate in a concentration range from 0 to 5 wt.% using a solvent casting technique. Agar diffusion test was performed to evaluate in-vitro antimicrobial properties of prepared samples. The obtained systems were characterized by tensile test, X-ray photoelectron spectroscopy, scanning electron microscopy, and optical microscopy. The micrographs revealed a better morphological disposition of silver particles along the polyvinyl chloride matrix in the samples cast from N,N-dimethylformamide. Nevertheless, the applied modification did not appreciably influence the tensile properties of the prepared systems compared to the reference samples.

Pre-Strain Stimulation of Electro-Mechanical Sensitivity of Carbon Nanotube Network/Polyurethane Composites

The change of electrical resistance of a highly extensible composite sensors consisting of a network of entangled multi-wall carbon nanotubes (CNTs) and thermoplastic polyurethane elastomer in the course of elongation was stimulated by initial tensile deformation. Though the initial deformation irreversibly changes the arrangement of CNT network, subsequent cyclic elongation and corresponding resistance change is stable. The resistance sensitivity, quantified by a gauge factor, which defines the sensitivity of strain sensor as the relative resistance change divided by the applied strain, increases nearly five times from the value of about five for not initially elongated composites. This is a substantial increase, which ranks the composites among materials with the highest electromechanical sensitivity. The observed sensitivity increase is discussed on basis of the cracking of a nanotube network with extension when the number of contacts between nanotubes decreases and thus the network has fewer interconnections that can carry an electric current.

Sonochemical synthesis of Gd3+ doped CoFe2O4 spinel ferrite nanoparticles and its physical properties

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe2-xGdxO4; x=0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd3+ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe2-xGdxO4 nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd3+ substitution in CoFe2O4 nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd3+ doped cobalt ferrite (CoFe2-xGdxO4; x=0.20) exhibit enhanced dielectric constant (277 at 100Hz) and ac conductivity (20.2×10-9S/cm at 100Hz). The modulus spectroscopy demonstrated the impact of Gd3+ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd3+ substitution from 234.32Oe (x=0.00) to 12.60Oe (x=0.05) and further increases from 12.60Oe (x=0.05) to 68.62Oe (x=0.20). Moreover, saturation magnetization decreases with Gd3+ substitution from 40.19emu/g (x=0.00) to 21.58emu/g (x=0.20). This work demonstrates that the grain size and cation distribution in Gd3+ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications.

Comparison of Vapor Sensing Properties of Pristine and Hexamethylene Diamine-Treated MWCNT Networks to Primary, Secondary and Tertiary Alcohols

The sensing properties of pristine and hexamethylene diamine (HDA)-treated multiwall carbon nanotube networks (MWCNT-Ns) to selected primary, secondary (sec-) and tertiary (ter-) alcohols were examined by resistance measurements. It was seen that sensor responses, S (%), of MWCNT (HDA)-N to these alcohols were much higher than those of the pristine network. An increase in the S (%) values per mm Hg of both networks was observed from propanol to butanol, when their values from primary alcohols to sec-/tert-ones decreased due to the change in the interaction area of these alcohols with the MWCNT-Ns.

Synthesis and Examination of Nanocomposites Based on Poly(2-hydroxyethyl methacrylate) for Medicinal Use

Preparation of poly(2-hydroxyethyl methacrylate) (PHEMA) based nanocomposites using different approaches such as synthesis with water as the porogen, filling of polymer matrix by silica and formation of interpenetrating polymer networks with polyurethane was demonstrated. Incorporation of various biologically active compounds (BAC) such as metronidazole, decamethoxin, zinc sulphate, silver nitrate or amino acids glycine and tryptophan into nanocomposites was achieved. BAC were introduced into the polymer matrix either (1) directly, or (2) with a solution of colloidal silica, or (3) through immobilization on silica (sol-densil). Morphology of prepared materials was investigated by laser scanning microscopy and low-vacuum scanning electron microscopy. In vacuum freeze-drying, prior imaging was proposed for improving visualization of the porous structure of composites. The interaction between PHEMA matrix and silica filler was investigated by IR spectroscopy. Adsorption of 2-hydroxyethyl methacrylate and BAC from aqueous solution on the silica surface was also examined. Phase composition and thermal stability of composites were studied by the differential thermogravimetry/differential thermal analysis. Release of BAC into water medium from prepared composites were shown to depend on the synthetic method and differed significantly. Obtained PHEMA-base materials which are characterized by controlled release of BAC have a strong potential for application in manufacturing of different surgical devices like implants, catheters and drainages.