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 30 nm results from TEM, XRD and magnetic analysis. Specific loss power is determined from hysteresis loops, susceptibility spectra and calorimetry with a maximum value of 960 W/g at 410 kHz and field amplitude 10 kA/m. Results may be understood by relaxation effects on hysteresis.
Recently, semitransparent luminescent solar concentrators (LSCs) have attracted a considerable at... more Recently, semitransparent luminescent solar concentrators (LSCs) have attracted a considerable attention 18 because they offer an easy and cost-effective route to harvest incident light. Various fluorophores including 19 semiconducting quantum dots and organic dyes have been prepared and utilized for LSC fabrication. 20 However, the narrow light absorption range, reabsorption losses, and limited photostability of the 21 fluorophores still hinder the widespread use of LSCs under outdoor and indoor light conditions. Here, we 22 rationally designed an LSC utilizing aggregation-induced emissive fluorophores (AIEgens) and an energy 23 transfer strategy. We employ diketopyrrolopyrrole with triphenylamine moiety as a highly stable AIEgen 24 that functions as an emissive energy-transfer acceptor in LSC; for a donor, we use tetraphenylethene 25 containing triphenylamine moiety that shows good aggregation-induced emission features and excellent 26 spectral overlap with the acceptor to yield an efficient energy transfer process. A thin-film LSC device with 27 an optimized donor : acceptor ratio (1 : 0.5) was fabricated. Under AM 1.5G solar spectrum, an LSC coupled 28 with three side reflectors and a backside diffuser exhibits 18% optical conversion efficiency and a 29 concentration factor of 1.18. Under indoor white LED illumination, the values were 27% and 1.68, 30 respectively. After exposed to intense UV radiations for 5 hours, the LSCs preserved 98% fluorescence 31 which suggests their superior long-term photostability. Our results suggest that the combination of AIEgens 32 and energy transfer holds the potential for enhancing the efficiency of the device and extended stability of 33 the fluorophores, two of the major requirements to allow industrial production and large-scale use of 34 outdoor/indoor light harvesting LSCs.
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...
Acoustic spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNT... more Acoustic spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNTs) functionalized by Fe 3 O 4 magnetic nanoparticles dissolved in transformer oil under the influence of a magnetic field at various temperatures. Three methods for the application of the magnetic field are used: a jump change, a linear increase or decrease and a constant magnetic field with a change of its orientation to the acoustic wave. The rearrangements of MWCNTs/Fe 3 O 4 to new structures (chains) by the influence of a magnetic field is confirmed by changes in the acoustic attenuation. From the measurement results, the lifetime of the chains after the switchoff of the magnetic field is less than 30 s. Such a rapid change is due to the fact that the nanotube chains are held by magnetic forces, resulting from the same direction of the magnetic moments of bound magnetic nanoparticles. A temperature-dependent hysteresis effect is observed with a linear change of the magnetic field. From our experiments, it follows that the reorientation of MWCNTs by magnetic nanoparticles with the magnetic field was gradual. The effect of the anisotropy of the acoustic attenuation is observed at a magnetic flux density of 200 mT and at various temperatures. Three MWCNT/Fe 3 O 4 concentrations diluted in the transformer oil are used for the measurements and their influences on the structural changes with various developments of the magnetic field are discussed.
The paper reports results of hyperthermia experiments performed with a magnetic fluid containing ... more The paper reports results of hyperthermia experiments performed with a magnetic fluid containing CoFe_2O_4 particles subjected to a magnetic field of a few intensities (0 < H_AC <=2350 Am^{-1}) and at the frequency f = 736 kHz. To determine the structure of the fluid and its magnetic properties, the magnetic measurements were made by a vibrating sample magnetometer (VSM) in a field, whose intensity was changed in a wide range (H = ± 800 kAm^{-1}). An additional study by the AFM method permitted estimation of the mean hydrodynamic volume of nanoparticles and the mean Brownian relaxation time of magnetisation. In the experimental conditions, the majority of the magnetic particles underwent demagnetization of the Brownian type te{Payet}. In order to determine the percent contribution of the hysteresis loss P_h to the total energy loss P_total, a few hysteresis loops (VSM) have been determined for the magnetic field amplitudes typical of medical applications H_AC < 30 kAm^{-1}. Tables 2, Figs 8, Refs 13.
Cerium dioxide nanoparticles (CeO 2) were synthesized by precipitation in the reversal microemuls... more Cerium dioxide nanoparticles (CeO 2) were synthesized by precipitation in the reversal microemulsions based on different surfactants. Crystallographic properties and morphology of CeO 2 nanoparticles were studied by X-ray diffraction method and transmission electron microscopy. It was established that CeO 2 nanoparticles synthesized in the reversal microemulsions had sizes in the range of 6-10 nm. Zeta-potential values of nanoparticles were measured by dynamic light scattering method and stability of CeO 2 in the aqueous suspension was estimated. It was shown that CeO 2 nanoparticles formed high-stable aqueous suspensions. It was studied that CeO 2 nanoparticles displayed catalase-like activity and they could be promising for development of the antioxidant nanomaterials for treatment of the sequences of oxidative stress.
Magnetic properties Magnetic properties D 9000 Magnetic Characteristics of LnNi 4 B Compounds (Ln... more Magnetic properties Magnetic properties D 9000 Magnetic Characteristics of LnNi 4 B Compounds (Ln: Y, Pr, Sm, Tb, Ho and Er).-The compounds LnNi 4 B (Ln: Y, Pr, Sm, Tb, Ho, Er) crystallize in the hexagonal space group P6/mmm. Magnetic measurements reveal superconducting behavior for YNi 4 B below approximately 12 K. The Pr containing compound is paramagnetic but contains a contribution of a ferromagnetic impurity phase. For compounds with Ln: Sm, Tb, Ho, and Er transitions to magnetically ordered states are observed at 38, 21, 6, and 12 K, respectively. SmNi 4 B exhibits a large magnetic hysteresis at 4.2 K with a coercive field above 7 T, which is one of the largest observed in Sm-transition metal compounds.
The efficiency of ultrasound hyperthermia for anti-cancer treatments such as radiotherapy or chem... more The efficiency of ultrasound hyperthermia for anti-cancer treatments such as radiotherapy or chemotherapy can be improved by using sonosensitizers, which are materials that enhance the attenuation and dissipation of acoustic energy. We propose the use of magnetic nanoparticles as sonosensitizers because of their biocompatibility, nontoxicity, and common use in several medical applications. A magnetic material was synthetized and then incorporated in the form of a magnetic fluid in agar tissue-mimicking phantoms. Ultrasound hyperthermia studies were conducted at various ultrasound frequencies and concentrations of magnetic nanoparticles in the phantoms. The theoretical modeling based on a heat transfer equation and the experimental results show good agreement and confirm that the temperature rise during ultrasound heating in tissue-mimicking phantoms doped with sonosensitizers is greater than that in a pure agar phantom. Furthermore, on the basis of Pennes' bio-heat equation, whi...
In this report, we show preparation of colloidally stable poly(N,N-dimethylacrylamide-co-acrylic ... more In this report, we show preparation of colloidally stable poly(N,N-dimethylacrylamide-co-acrylic acid) (DMA)- and D-mannose (MAN)-coated maghemite nanoparticles and their ability to generate heat in an alternating magnetic field, which could make the particles applicable for hyperthermic therapy of cancer. The particles are obtained by coprecipitation reaction and characterized by transmission electron microscopy, dynamic light scattering, and AC calorimetric measurement of heat generated by the particles. While the dry particles were ca. 10 nm in diameter, their hydrodynamic size in water was within the range of 100 nm. Heating characteristics were measured in an LC circuit with a maximum field intensity of 6.8 kA m−1 and frequency 190 kHz. The specific absorption rates of γ-Fe2O3, PDM@γ-Fe2O3, and MAN@γ-Fe2O3 nanoparticles were extrapolated to 10 kA m−1, reaching about 15 W g−1.
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
In the present paper, we provide low-frequency dielectric spectra for a thin layer of a nanofluid... more In the present paper, we provide low-frequency dielectric spectra for a thin layer of a nanofluid based on transformer oil and iron oxide nanoparticles stabilized by oleic acid. The complex dielectric permittivity measured in the frequency range from 1 mHz to 200 kHz shows an obvious electrode polarization effect and a Debye-like dielectric relaxation process. Both effects stem from the presence of space charge in the oil due to impurity ions, and in the nanofluid represented predominantly by a residual surfactant and uncompensated particle surface charge. It is shown that the spectra, which were measured in the temperature range from 298 K to 358 K, can be well represented by a fitting function consisted of one Havriliak-Negami term and the Jonscher’s power law. In the investigated magnetic nanofluid layer, we found that the onset of the electrode polarization is suppressed to lower frequencies by the application of an external magnetic field (300 mT). This phenomenon is explained ...
Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fiel... more Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation pro...
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 30 nm results from TEM, XRD and magnetic analysis. Specific loss power is determined from hysteresis loops, susceptibility spectra and calorimetry with a maximum value of 960 W/g at 410 kHz and field amplitude 10 kA/m. Results may be understood by relaxation effects on hysteresis.
Recently, semitransparent luminescent solar concentrators (LSCs) have attracted a considerable at... more Recently, semitransparent luminescent solar concentrators (LSCs) have attracted a considerable attention 18 because they offer an easy and cost-effective route to harvest incident light. Various fluorophores including 19 semiconducting quantum dots and organic dyes have been prepared and utilized for LSC fabrication. 20 However, the narrow light absorption range, reabsorption losses, and limited photostability of the 21 fluorophores still hinder the widespread use of LSCs under outdoor and indoor light conditions. Here, we 22 rationally designed an LSC utilizing aggregation-induced emissive fluorophores (AIEgens) and an energy 23 transfer strategy. We employ diketopyrrolopyrrole with triphenylamine moiety as a highly stable AIEgen 24 that functions as an emissive energy-transfer acceptor in LSC; for a donor, we use tetraphenylethene 25 containing triphenylamine moiety that shows good aggregation-induced emission features and excellent 26 spectral overlap with the acceptor to yield an efficient energy transfer process. A thin-film LSC device with 27 an optimized donor : acceptor ratio (1 : 0.5) was fabricated. Under AM 1.5G solar spectrum, an LSC coupled 28 with three side reflectors and a backside diffuser exhibits 18% optical conversion efficiency and a 29 concentration factor of 1.18. Under indoor white LED illumination, the values were 27% and 1.68, 30 respectively. After exposed to intense UV radiations for 5 hours, the LSCs preserved 98% fluorescence 31 which suggests their superior long-term photostability. Our results suggest that the combination of AIEgens 32 and energy transfer holds the potential for enhancing the efficiency of the device and extended stability of 33 the fluorophores, two of the major requirements to allow industrial production and large-scale use of 34 outdoor/indoor light harvesting LSCs.
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...
Acoustic spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNT... more Acoustic spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNTs) functionalized by Fe 3 O 4 magnetic nanoparticles dissolved in transformer oil under the influence of a magnetic field at various temperatures. Three methods for the application of the magnetic field are used: a jump change, a linear increase or decrease and a constant magnetic field with a change of its orientation to the acoustic wave. The rearrangements of MWCNTs/Fe 3 O 4 to new structures (chains) by the influence of a magnetic field is confirmed by changes in the acoustic attenuation. From the measurement results, the lifetime of the chains after the switchoff of the magnetic field is less than 30 s. Such a rapid change is due to the fact that the nanotube chains are held by magnetic forces, resulting from the same direction of the magnetic moments of bound magnetic nanoparticles. A temperature-dependent hysteresis effect is observed with a linear change of the magnetic field. From our experiments, it follows that the reorientation of MWCNTs by magnetic nanoparticles with the magnetic field was gradual. The effect of the anisotropy of the acoustic attenuation is observed at a magnetic flux density of 200 mT and at various temperatures. Three MWCNT/Fe 3 O 4 concentrations diluted in the transformer oil are used for the measurements and their influences on the structural changes with various developments of the magnetic field are discussed.
The paper reports results of hyperthermia experiments performed with a magnetic fluid containing ... more The paper reports results of hyperthermia experiments performed with a magnetic fluid containing CoFe_2O_4 particles subjected to a magnetic field of a few intensities (0 < H_AC <=2350 Am^{-1}) and at the frequency f = 736 kHz. To determine the structure of the fluid and its magnetic properties, the magnetic measurements were made by a vibrating sample magnetometer (VSM) in a field, whose intensity was changed in a wide range (H = ± 800 kAm^{-1}). An additional study by the AFM method permitted estimation of the mean hydrodynamic volume of nanoparticles and the mean Brownian relaxation time of magnetisation. In the experimental conditions, the majority of the magnetic particles underwent demagnetization of the Brownian type te{Payet}. In order to determine the percent contribution of the hysteresis loss P_h to the total energy loss P_total, a few hysteresis loops (VSM) have been determined for the magnetic field amplitudes typical of medical applications H_AC < 30 kAm^{-1}. Tables 2, Figs 8, Refs 13.
Cerium dioxide nanoparticles (CeO 2) were synthesized by precipitation in the reversal microemuls... more Cerium dioxide nanoparticles (CeO 2) were synthesized by precipitation in the reversal microemulsions based on different surfactants. Crystallographic properties and morphology of CeO 2 nanoparticles were studied by X-ray diffraction method and transmission electron microscopy. It was established that CeO 2 nanoparticles synthesized in the reversal microemulsions had sizes in the range of 6-10 nm. Zeta-potential values of nanoparticles were measured by dynamic light scattering method and stability of CeO 2 in the aqueous suspension was estimated. It was shown that CeO 2 nanoparticles formed high-stable aqueous suspensions. It was studied that CeO 2 nanoparticles displayed catalase-like activity and they could be promising for development of the antioxidant nanomaterials for treatment of the sequences of oxidative stress.
Magnetic properties Magnetic properties D 9000 Magnetic Characteristics of LnNi 4 B Compounds (Ln... more Magnetic properties Magnetic properties D 9000 Magnetic Characteristics of LnNi 4 B Compounds (Ln: Y, Pr, Sm, Tb, Ho and Er).-The compounds LnNi 4 B (Ln: Y, Pr, Sm, Tb, Ho, Er) crystallize in the hexagonal space group P6/mmm. Magnetic measurements reveal superconducting behavior for YNi 4 B below approximately 12 K. The Pr containing compound is paramagnetic but contains a contribution of a ferromagnetic impurity phase. For compounds with Ln: Sm, Tb, Ho, and Er transitions to magnetically ordered states are observed at 38, 21, 6, and 12 K, respectively. SmNi 4 B exhibits a large magnetic hysteresis at 4.2 K with a coercive field above 7 T, which is one of the largest observed in Sm-transition metal compounds.
The efficiency of ultrasound hyperthermia for anti-cancer treatments such as radiotherapy or chem... more The efficiency of ultrasound hyperthermia for anti-cancer treatments such as radiotherapy or chemotherapy can be improved by using sonosensitizers, which are materials that enhance the attenuation and dissipation of acoustic energy. We propose the use of magnetic nanoparticles as sonosensitizers because of their biocompatibility, nontoxicity, and common use in several medical applications. A magnetic material was synthetized and then incorporated in the form of a magnetic fluid in agar tissue-mimicking phantoms. Ultrasound hyperthermia studies were conducted at various ultrasound frequencies and concentrations of magnetic nanoparticles in the phantoms. The theoretical modeling based on a heat transfer equation and the experimental results show good agreement and confirm that the temperature rise during ultrasound heating in tissue-mimicking phantoms doped with sonosensitizers is greater than that in a pure agar phantom. Furthermore, on the basis of Pennes' bio-heat equation, whi...
In this report, we show preparation of colloidally stable poly(N,N-dimethylacrylamide-co-acrylic ... more In this report, we show preparation of colloidally stable poly(N,N-dimethylacrylamide-co-acrylic acid) (DMA)- and D-mannose (MAN)-coated maghemite nanoparticles and their ability to generate heat in an alternating magnetic field, which could make the particles applicable for hyperthermic therapy of cancer. The particles are obtained by coprecipitation reaction and characterized by transmission electron microscopy, dynamic light scattering, and AC calorimetric measurement of heat generated by the particles. While the dry particles were ca. 10 nm in diameter, their hydrodynamic size in water was within the range of 100 nm. Heating characteristics were measured in an LC circuit with a maximum field intensity of 6.8 kA m−1 and frequency 190 kHz. The specific absorption rates of γ-Fe2O3, PDM@γ-Fe2O3, and MAN@γ-Fe2O3 nanoparticles were extrapolated to 10 kA m−1, reaching about 15 W g−1.
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
In the present paper, we provide low-frequency dielectric spectra for a thin layer of a nanofluid... more In the present paper, we provide low-frequency dielectric spectra for a thin layer of a nanofluid based on transformer oil and iron oxide nanoparticles stabilized by oleic acid. The complex dielectric permittivity measured in the frequency range from 1 mHz to 200 kHz shows an obvious electrode polarization effect and a Debye-like dielectric relaxation process. Both effects stem from the presence of space charge in the oil due to impurity ions, and in the nanofluid represented predominantly by a residual surfactant and uncompensated particle surface charge. It is shown that the spectra, which were measured in the temperature range from 298 K to 358 K, can be well represented by a fitting function consisted of one Havriliak-Negami term and the Jonscher’s power law. In the investigated magnetic nanofluid layer, we found that the onset of the electrode polarization is suppressed to lower frequencies by the application of an external magnetic field (300 mT). This phenomenon is explained ...
Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fiel... more Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation pro...
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