Ivo Kuritka

The Electrorheological Behavior of Suspensions Based on Molten-Salt Synthesized Lithium Titanate Nanoparticles and Their Core–Shell Titanate/Urea Analogues

This paper concerns the preparation of novel electrorheological (ER) materials using microwave-assisted synthesis as well as utilizing a suitable shell-providing system with enhanced ER performance. Lithium titanate nanoparticles were successfully synthesized, and their composition was confirmed via X-ray diffraction. Rheological properties were investigated in the absence as well as in the presence of an external electric field. Dielectric properties clarified the response of the particles to the application of an electric field. The urea-coated lithium titanate nanoparticle-based suspension exhibits higher ER performance in comparison to suspensions based on bare particles.

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.

Microwave solvothermal decoration of the cellulose surface by nanostructured hybrid Ag/ZnO particles: a joint XPS, XRD and SEM study

The synthesis of hybrid silver/zinc oxide (Ag/ZnO) decoration on the cellulose surface is described. The structures were characterized with X-ray photoelectron spectroscopy (XPS) and corroborated with X-ray diffraction and scanning electron microscopy. Silver nitrate and zinc acetate dihydrate were used as soluble raw materials. Hexamethylenetetraamine was used as the precipitating and reducing agent. The surface of α-cellulose was always treated by hydrogen peroxide before synthesis with a relatively mild effect manifested in water contact angle measurement and XPS high-resolution spectra. The Ag/ZnO decoration system was identified as a true nanodispersed metal/semiconductor hybrid with a unique collective plasmonic structure observed on Ag 3d core lines for the first time. A series of experiments with a single precursor solution contributed to the characterization of the interaction of Ag+ and Zn2+ species with the surface and to the description of the reaction mechanism in the mixed precursor solution. In contrast to previous reports, a specific interaction between the cellulose substrate and Zn2+ was observed. No specific non-thermal effects of microwave heating were observed.

Characterization of Antibacterial Polymeric Films Based on Poly(vinyl alcohol) and Zinc Nitrate for Biomedical Applications

Abstract Poly(vinyl alcohol) (PVA) was modified by zinc nitrate in the concentration range from 0 to 22.29 wt.% using the solvent cast technique. The resulting material was characterized by optical microscopy, stress-strain analysis, differential scanning calorimetry, UV-visible spectroscopy, and Fourier transform-infrared spectroscopy. In addition, the antibacterial properties of the prepared films were tested against the both gram positive and gram negative bacterial strains. The results show the uniform distribution of the modifier within the PVA matrix, enhanced mechanical properties (up to 8.24 wt.%), and good antibacterial activity against gram negative bacteria at low modifier content.

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.

Modification of poly(vinyl alcohol) with lactose and calcium lactate: potential filler from dairy industry

Abstract Characteristics of a newly developed environmentally friendly biocomposite material, poly(vinyl alcohol) (PVA) modified with lactose and calcium lactate, potential fillers, byproduct of dairy industry, are reported in the present paper. Sample films containing 0, 10, 20, 33 and 42 wt-% of filler were prepared by conventional solvent casting into acrylic plates. Morphological, mechanical and thermal properties of PVA, PVA–lactose and PVA–calcium lactate composites were studied by optical microscopy, stress–strain analysis, Fourier transform infrared spectroscopy–attenuated total reflectance (FTIR–ATR), differential scanning calorimetry, thermogravimetric analysis (TGA), and also the biodegradability was tested. The films were thin and transparent, and became gradually white with increasing concentration of the filler. Optical microscopy and FTIR–ATR analysis of PVA–lactose and PVA–calcium lactate confirmed that they are composite materials. Their mechanical properties increased up to 33 wt-% filler. The glass transition temperature also decreased with rising content of filler, which indicates the influence of moisture absorbed by the composites (confirmed by TGA measurements). Poly(vinyl alcohol) modification with lactose showed that the biodegradability is improved in aqueous environment.

Construction of antibacterial poly(ethylene terephthalate) films via layer by layer assembly of chitosan and hyaluronic acid

Polyelectrolytic multilayers (PEMs) with enhanced antibacterial properties were built up onto commercial poly(ethylene terephthalate) (PET) films based on the layer by layer assembling of bacterial contact killing chitosan and bacterial repelling highly hydrated hyaluronic acid. The optimization of the aminolysis modification reaction of PET was carried out by the study of the mechanical properties and the surface characterization of the modified polymers. The layer by layer assembly was successfully monitored by TEM microscopy, surface zeta-potential, contact angle measurements and, after labeling with fluorescein isothiocyanate (FTIC) by absorption spectroscopy and confocal fluorescent microscopy. Beside, the stability of the PEMs was studied at physiological conditions in absence and in the presence of lysozyme and hyaluronidase enzymes. Antibacterial properties of the obtained PEMs against Escherichia coli were compared with original commercial PET.

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.

Polyolefin Backbone Substitution in Binders for Low Temperature Powder Injection Moulding Feedstocks

This paper reports the substitution of polyolefin backbone binder components with low melting temperature carnauba wax for powder injection moulding applications. The effect of various binder compositions of Al2O3 feedstock on thermal degradation parameters is investigated by thermogravimetric analysis. Within the experimental framework 29 original feedstock compositions were prepared and the superiority of carnauba wax over the polyethylene binder backbone was demonstrated in compositions containing polyethylene glycol as the initial opening agent and governing the proper mechanism of the degradation process. Moreover, the replacement of synthetic polymer by the natural wax contributes to an increase of environmental sustainability of modern industrial technologies.