The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been c... more The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been consisted of magnetit particles (Fe3O4) of nanometric size that were coated with oleic acid as a surfactant and dispersed in transformer oil. The DC electric and constant magnetic fields have affected on MFs simultaneously and electro-physical processes, which influence electric breakdown, were obserwed. The especial attention was devoted to pre-breakdown, breakdown and postbreakdown state in MFs. Słowa kluczowe: przebicie elektryczne, stany przedprzebiciowe, przebicia i poprzebiciowe, ciecz magnetyczna, pola elektryczne i magnetyczne, strukturalizacja cząstek magnetycznych
The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in t... more The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in the ultralow frequency regime was investigated. A dielectric relaxation, whose relaxation time is 160 s, is observed at 303 K, and the dielectric relaxation is found to be independent of applied electric field. It is shown that the dielectric relaxation is caused by the Helmholtz double layer formed by the adsorption of impurity ions in 5CB onto the electrode surfaces of the cells, and hence the thickness of the double layer is comparable to the radius of impurity ions in 5CB. The dielectric relaxation obeys the empirical Cole‐Cole circular arc law, indicating that dielectric relaxation times are distributed. The distribution of dielectric relaxation times can be explained in terms of distributed thicknesses of the Helmholtz double layer.
Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)a... more Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)applications. Multimodal imaging as well as simultaneous control and monitoring of intracellular movements profit from the combination of these functionalities. Accordingly, several methods have been developed for the synthesis of magnetic fluorescent particles. The majority of these methods, however, require complex modification and purification steps and result in a low yield of particles. Here, we describe a straightforward and scalable method for the magnetic modification of cellulose-based fluorescent particles. The method is based on the use of microwave-synthesized magnetite nanoparticles prepared from ferrous sulfate at high pH. Magnetic modification did not change the pH sensitivity or the optical properties of the fluorescent particles, and allowed them to be manipulated by external magnetic field. Our results demonstrate the possibility of large scale, easy production of bifunctional particles. We anticipate that our method can be expanded to include other types of particles or functionalities relevant for biomedical applications.
Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. T... more Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. They appear to be a suitable carrier for the targeted drug transport, which represents a new method of cancer treatment. Advantages of targeted drugs transport are the minimizing of hurt to the organism, specific focusing on certain types of tissues, increased effect of the drug, reduced drug dose and hence side effects. The main goal of the present study was to verify the effect of bacterial magnetic nanoparticles produced by
Liquid crystals (LCs) composed of mesogens play important roles in various scientific and enginee... more Liquid crystals (LCs) composed of mesogens play important roles in various scientific and engineering problems. How a system with many mesogens can enter a LC state is an interesting and important problem. Using stiff and free-joint Lennard-Jones chain molecules as mesogens, we study the conditions under which the mesogens can enter various LC phases. The guideline is to eliminate the unwanted translational orders under a controlled fine-tuning procedure across a sequence of systems. Instead of monitoring the growth of order out of the disorder, we prepare a configuration of high orientation ordering and find out where it relaxes to. Such a procedure begins with a reference system, consisting of short chains of homogeneous soft spheres, in a liquid-vapor coexistence situation, at which the thermodynamic instability triggers a fast spontaneous growing process. By applying a short pulse of auxiliary field to align the dispersedly oriented clusters, followed by reducing the volume and,...
A broadband dielectric response of ferrofluids can be effectively controlled by application of an... more A broadband dielectric response of ferrofluids can be effectively controlled by application of an external magnetic field. The interaction of magnetic nanoparticles with magnetic forces and the resulting structural changes in the ferrofluids may tune their dielectric spectra. In this paper, we present an experimental study on the controllability of a dielectric spectrum of Mn-Zn ferrite transformer oil-based ferrofluid by means of a static electric field generated by a direct current (DC) bias voltage. Two experimental configurations of the DC bias voltage are applied. The spectrum of a complex permittivity measured in the frequency range from 1 mHz up to 200 kHz is firstly studied under an internal DC bias voltage applied on the electrodes of a measuring capacitor. Then, the sensitivity of the dielectric spectrum to the external DC bias voltage applied on an external pair of electrodes outside the measuring capacitor is investigated. It is found that the increasing internal DC bias...
Control of the size and spatial distribution of materials at multiple length scales is one of the... more Control of the size and spatial distribution of materials at multiple length scales is one of the most compelling issues in nanotechnology research. We report a multiple-length-scale patterning of pure magnetic particles as well as biocompatible magnetic particles based on a printing technique named micro-injection molding in capillaries. The magnetic particles were prepared by a technique of co-precipitation of ferric and ferrous salts in an alkali medium. We demonstrate that the morphology and the size of the patterning nanoparticles can be controlled by simply controlling the concentration of the solution. Our method exploits the self-organization of the nanoparticles in a solution confined between a stamp and the surfaces of a substrate, exploiting confinement and competing interactions between the adsorbate and the substrate. Our approach represents a remarkable example of an integrated top-down/bottom-up process.
The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and th... more The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and the carrier liquid. The structural changes in magnetic fluids with different nanoparticle diameter based on transformer oils TECHNOL and MOGUL under the effect of a magnetic field and temperature were studied by acoustic spectroscopy. At a linear and jump changes of the magnetic field at various temperatures a continuous change was observed of acoustic attenuation caused by aggregation of the magnetic nanoparticles to structures. From the anisotropy of acoustic attenuation and using the Taketomi theory the basic parameters of the structures are calculated and the impact of nanoparticle diameters on the size of structures is confirmed.
Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core... more Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core diameter of about 30nm results from TEM, XRD and magnetic analysis. Specific loss power is determined from hysteresis loops, susceptibility spectra and calorimetry with ...
Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse sp... more Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse spleen ferritin (HSF) and nanoscale magnetite aqueous suspensions. The anisotropy of optical polarizability was calculated. The average magnetic dipole moment calculated assuming the Langevin model was about 20,000 and 8500μB per particle, for magnetite nanoparticle and magnetoferritin, respectively. Poor fitting results and the unphysical value of average magnetic moment
The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been c... more The development of electric breakdown in magnetic fluids (MFs) has been analyzed. MFs have been consisted of magnetit particles (Fe3O4) of nanometric size that were coated with oleic acid as a surfactant and dispersed in transformer oil. The DC electric and constant magnetic fields have affected on MFs simultaneously and electro-physical processes, which influence electric breakdown, were obserwed. The especial attention was devoted to pre-breakdown, breakdown and postbreakdown state in MFs. Słowa kluczowe: przebicie elektryczne, stany przedprzebiciowe, przebicia i poprzebiciowe, ciecz magnetyczna, pola elektryczne i magnetyczne, strukturalizacja cząstek magnetycznych
The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in t... more The dielectric properties of nematic liquid crystal (4‐cyano‐4′‐n‐pentylbiphenyl: 5CB) cells in the ultralow frequency regime was investigated. A dielectric relaxation, whose relaxation time is 160 s, is observed at 303 K, and the dielectric relaxation is found to be independent of applied electric field. It is shown that the dielectric relaxation is caused by the Helmholtz double layer formed by the adsorption of impurity ions in 5CB onto the electrode surfaces of the cells, and hence the thickness of the double layer is comparable to the radius of impurity ions in 5CB. The dielectric relaxation obeys the empirical Cole‐Cole circular arc law, indicating that dielectric relaxation times are distributed. The distribution of dielectric relaxation times can be explained in terms of distributed thicknesses of the Helmholtz double layer.
Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)a... more Fluorescent and magnetic nano- and microparticles have already been used for wide range of (bio)applications. Multimodal imaging as well as simultaneous control and monitoring of intracellular movements profit from the combination of these functionalities. Accordingly, several methods have been developed for the synthesis of magnetic fluorescent particles. The majority of these methods, however, require complex modification and purification steps and result in a low yield of particles. Here, we describe a straightforward and scalable method for the magnetic modification of cellulose-based fluorescent particles. The method is based on the use of microwave-synthesized magnetite nanoparticles prepared from ferrous sulfate at high pH. Magnetic modification did not change the pH sensitivity or the optical properties of the fluorescent particles, and allowed them to be manipulated by external magnetic field. Our results demonstrate the possibility of large scale, easy production of bifunctional particles. We anticipate that our method can be expanded to include other types of particles or functionalities relevant for biomedical applications.
Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. T... more Magnetosomes are nanoparticles coated with organic membrane produced by magnetotactic bacteria. They appear to be a suitable carrier for the targeted drug transport, which represents a new method of cancer treatment. Advantages of targeted drugs transport are the minimizing of hurt to the organism, specific focusing on certain types of tissues, increased effect of the drug, reduced drug dose and hence side effects. The main goal of the present study was to verify the effect of bacterial magnetic nanoparticles produced by
Liquid crystals (LCs) composed of mesogens play important roles in various scientific and enginee... more Liquid crystals (LCs) composed of mesogens play important roles in various scientific and engineering problems. How a system with many mesogens can enter a LC state is an interesting and important problem. Using stiff and free-joint Lennard-Jones chain molecules as mesogens, we study the conditions under which the mesogens can enter various LC phases. The guideline is to eliminate the unwanted translational orders under a controlled fine-tuning procedure across a sequence of systems. Instead of monitoring the growth of order out of the disorder, we prepare a configuration of high orientation ordering and find out where it relaxes to. Such a procedure begins with a reference system, consisting of short chains of homogeneous soft spheres, in a liquid-vapor coexistence situation, at which the thermodynamic instability triggers a fast spontaneous growing process. By applying a short pulse of auxiliary field to align the dispersedly oriented clusters, followed by reducing the volume and,...
A broadband dielectric response of ferrofluids can be effectively controlled by application of an... more A broadband dielectric response of ferrofluids can be effectively controlled by application of an external magnetic field. The interaction of magnetic nanoparticles with magnetic forces and the resulting structural changes in the ferrofluids may tune their dielectric spectra. In this paper, we present an experimental study on the controllability of a dielectric spectrum of Mn-Zn ferrite transformer oil-based ferrofluid by means of a static electric field generated by a direct current (DC) bias voltage. Two experimental configurations of the DC bias voltage are applied. The spectrum of a complex permittivity measured in the frequency range from 1 mHz up to 200 kHz is firstly studied under an internal DC bias voltage applied on the electrodes of a measuring capacitor. Then, the sensitivity of the dielectric spectrum to the external DC bias voltage applied on an external pair of electrodes outside the measuring capacitor is investigated. It is found that the increasing internal DC bias...
Control of the size and spatial distribution of materials at multiple length scales is one of the... more Control of the size and spatial distribution of materials at multiple length scales is one of the most compelling issues in nanotechnology research. We report a multiple-length-scale patterning of pure magnetic particles as well as biocompatible magnetic particles based on a printing technique named micro-injection molding in capillaries. The magnetic particles were prepared by a technique of co-precipitation of ferric and ferrous salts in an alkali medium. We demonstrate that the morphology and the size of the patterning nanoparticles can be controlled by simply controlling the concentration of the solution. Our method exploits the self-organization of the nanoparticles in a solution confined between a stamp and the surfaces of a substrate, exploiting confinement and competing interactions between the adsorbate and the substrate. Our approach represents a remarkable example of an integrated top-down/bottom-up process.
The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and th... more The properties of magnetic fluids depend on the nanoparticle diameter, their concentration and the carrier liquid. The structural changes in magnetic fluids with different nanoparticle diameter based on transformer oils TECHNOL and MOGUL under the effect of a magnetic field and temperature were studied by acoustic spectroscopy. At a linear and jump changes of the magnetic field at various temperatures a continuous change was observed of acoustic attenuation caused by aggregation of the magnetic nanoparticles to structures. From the anisotropy of acoustic attenuation and using the Taketomi theory the basic parameters of the structures are calculated and the impact of nanoparticle diameters on the size of structures is confirmed.
Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core... more Suspensions of bacterial magnetosomes are investigated with respect to magnetic losses. Mean core diameter of about 30nm results from TEM, XRD and magnetic analysis. Specific loss power is determined from hysteresis loops, susceptibility spectra and calorimetry with ...
Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse sp... more Magnetically induced optical birefringence (Δn) was measured for magnetoferritin (MFer), horse spleen ferritin (HSF) and nanoscale magnetite aqueous suspensions. The anisotropy of optical polarizability was calculated. The average magnetic dipole moment calculated assuming the Langevin model was about 20,000 and 8500μB per particle, for magnetite nanoparticle and magnetoferritin, respectively. Poor fitting results and the unphysical value of average magnetic moment
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Papers by Milan Timko