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  • 1.
    Ahniyaz, Anwar
    et al.
    Stockholm University, Sweden.
    Seisenbaeva, Gulaim A.
    SLU Swedish University of Agricultural Sciences, Sweden.
    Häggström, Lennart
    Uppsala University, Sweden.
    Kamali, Saeed
    Uppsala University, Sweden.
    Kessler, Vadim G.
    SLU Swedish University of Agricultural Sciences, Sweden.
    Nordblad, Per
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Bergström, Lennart
    Stockholm University, Sweden.
    Preparation of iron oxide nanocrystals by surfactant-free or oleic acid-assisted thermal decomposition of a Fe(III) alkoxide2008In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, p. 781-787Article in journal (Refereed)
    Abstract [en]

    A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mössbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope.

  • 2.
    Ahrentorp, Fredrik
    et al.
    RISE, Swedish ICT, Acreo.
    Astalan, Andrea
    RISE, Swedish ICT, Acreo.
    Blomgren, Jakob
    RISE, Swedish ICT, Acreo.
    Jonasson, Christian
    RISE, Swedish ICT, Acreo.
    Wetterskog, Erik
    Uppsala University, Sweden.
    Svedlindh, Peter
    Uppsala University, Sweden.
    Lak, Aidin
    Technical University of Braunschweig, Germany.
    Ludwig, Frank
    Technical University of Braunschweig, Germany.
    van Ijzendoorn, Leo J.
    Eindhoven University of Technology, The Netherlands.
    Westphal, Fritz
    Micromod Partikeltechnologie GmbH, Germany.
    Gruttner, Cordula
    Micromod Partikeltechnologie GmbH, Germany.
    Gehrke, Nicole
    nanoPET Pharma GmbH, Germany.
    Gustafsson, Stefan
    Chalmers University of Technology, Sweden.
    Olsson, Eva
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Effective particle magnetic moment of multi-core particles2015In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 380, p. 221-226Article in journal (Refereed)
    Abstract [en]

    In this study we investigate the magnetic behavior of magnetic multi-core particles and the differences in the magnetic properties of multi-core and single-core nanoparticles and correlate the results with the nanostructure of the different particles as determined from transmission electron microscopy(TEM). We also investigate how the effective particle magnetic moment is coupled to the individual moments of the single-domain nanocrystals by using different measurement techniques: DC magnetometry, AC susceptometry, dynamic light scattering and TEM. We have studied two magnetic multi-core particle systems – BNF Starch from Micromod with a median particle diameter of 100 nm and FeraSpin R from nanoPET with a median particle diameter of 70 nm – and one single-core particle system – SHP25 from Ocean NanoTech with a median particle core diameter of 25 nm.

  • 3.
    Ahrentorp, Fredrik
    et al.
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Blomgren, Jakob
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Jonasson, Christian
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Sarwe, Anna
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Sepehri, Sobhan
    Chalmers University of Technology, Sweden.
    Eriksson, Emil
    Chalmers University of Technology, Sweden.
    Kalaboukhov, Alexei
    Chalmers University of Technology, Sweden.
    Jesorka, Aldo
    Chalmers University of Technology, Sweden.
    Winkler, Dag
    Chalmers University of Technology, Sweden.
    Schneiderman, Justin F.
    University of Gothenburg, Sweden.
    Nilsson, Mats
    Stockholm University, Sweden.
    Albert, Jan
    Karolinska University Hospital, Sweden; Karolinska Institute, Sweden.
    de la Torre, Theresa Z. G.
    Uppsala University, Sweden.
    Strømme, Maria
    Uppsala University, Sweden.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Sensitive magnetic biodetection using magnetic multi-core nanoparticles and RCA coils2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 427, p. 14-18Article in journal (Refereed)
    Abstract [en]

    We use functionalized iron oxide magnetic multi-core particles of 100 nm in size (hydrodynamic particle diameter) and AC susceptometry (ACS) methods to measure the binding reactions between the magnetic nanoparticles (MNPs) and bio-analyte products produced from DNA segments using the rolling circle amplification (RCA) method. We use sensitive induction detection techniques in order to measure the ACS response. The DNA is amplified via RCA to generate RCA coils with a specific size that is dependent on the amplification time. After about 75 min of amplification we obtain an average RCA coil diameter of about 1 µm. We determine a theoretical limit of detection (LOD) in the range of 11 attomole (corresponding to an analyte concentration of 55 fM for a sample volume of 200 µL) from the ACS dynamic response after the MNPs have bound to the RCA coils and the measured ACS readout noise. We also discuss further possible improvements of the LOD.

  • 4.
    Chakkarapani, Prabu
    et al.
    Anna University, India.
    Subbiah, Latha
    Anna University, India.
    Palanisamy, Selvamani
    Anna University, India.
    Bibiana, Arputha
    Anna University, India.
    Ahrentorp, Fredrik
    RISE, Swedish ICT, Acreo.
    Jonasson, Christian
    RISE, Swedish ICT, Acreo.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Encapsulation of methotrexate loaded magnetic microcapsules for magnetic drug targeting and controlled drug release2015In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 380, p. 285-294Article in journal (Refereed)
    Abstract [en]

    We report on the development and evaluation of methotrexate magnetic microcapsules (MMC) for targeted rheumatoid arthritis therapy. Methotrexate was loaded into CaCO3-PSS (poly (sodium 4-styrenesulfonate)) doped microparticles that were coated successively with poly (allylamine hydrochloride) and poly (sodium 4-styrenesulfonate) by layer-by-layer technique. Ferrofluid was incorporated between the polyelectrolyte layers. CaCO3-PSS core was etched by incubation with EDTA yielding spherical MMC. The MMC were evaluated for various physicochemical, pharmaceutical parameters and magnetic properties. Surface morphology, crystallinity, particle size, zeta potential, encapsulation efficiency, loading capacity, drug release pattern, release kinetics and AC susceptibility studies revealed spherical particles of ~3 µm size were obtained with a net zeta potential of +24.5 mV, 56% encapsulation and 18.6% drug loading capacity, 96% of cumulative drug release obeyed Hixson-Crowell model release kinetics. Drug excipient interaction, surface area, thermal and storage stability studies for the prepared MMC was also evaluated. The developed MMC offer a promising mode of targeted and sustained release drug delivery for rheumatoid arthritis therapy.

  • 5.
    Fonnum, Geir
    et al.
    Dynal Biotech ASA, Norway.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Molteberg, Astrid
    Dynal Biotech ASA, Norway.
    Aksnes, Elin
    Dynal Biotech ASA, Norway.
    Mörup, Steen
    DTU Technical University of Denmark, Denmark.
    Characterization of Dynabeads® by magnetization measurements Mössbauer spectroscopy2005In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 293, p. 41-47Article in journal (Refereed)
    Abstract [en]

    X-ray diffraction, SEM analysis, Mössbauer spectroscopy and magnetic measurements were used to characterize three different magnetic beads (Dynabeads®). Maghemite (γ-Fe2O3) is the predominant crystalline phase. The nanoparticles were evenly spread in the beads, and the crystal sizes were in the range of 8 nm. The nanoparticles showed superparamagnetic behaviour. The particle's intrinsic magnetization of about 340 kA/m is typical for nanoparticles of maghemite.

  • 6.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Ivanov, Zdravko G.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Kislinski, Yu V.
    Chalmers University of Technology, Sweden; Russian Academy of Sciences, Russia.
    Larsson, Peter O.
    Chalmers University of Technology, Sweden.
    A magnetic phase transition studied with high TC SQUIDs1998In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 177, p. 519-520Article in journal (Refereed)
    Abstract [en]

    We have used high-Tc SQUIDs to study the phase transition in a film of Mn3O4. The film was positioned on top of the SQUID, and the temperature of the film and the SQUID was varied in the range 30-60 K. By monitoring the voltage at the SQUID output we were able to observe a reproducable shift in the SQUID response in the range 30-50 K. This shift is related to the transition from the paramagnetic to the ferrimagnetic state of the Mn3O4 film.

  • 7.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Interaction effects in the dynamic response of magnetic liquids1991In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 101, p. 45-46Article in journal (Refereed)
    Abstract [en]

    The magnetic susceptibility of magnetic liquids has been measured for frequencies up to 70 MHz. The imaginary part of the susceptibility exhibits a maximum around 10 MHz. This feature is interpreted as due to single-particle Néel relaxation, where particle interactions cause a slight concentration dependence in the position of the maximum.

  • 8.
    Hanson, Maj
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Nilsson, Bengt A.
    Chalmers University of Technology, Sweden.
    Svedberg, Erik Björn
    Seagate Research, USA.
    Magnetic properties of epitaxial Ni (001) films sub-micron particles2001In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 236, p. 139-50Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of Ni particles with well-defined geometry, prepared by electron lithography from epitaxial Ni (001) films of thickness 50 and 60nm were studied. The particles were circles with diameters 0.6μm and rectangles with sides 0.9μm and 0.3μm, that were positioned in square and rectangular lattices, having lattice constants about twice the particle dimensions. Reference samples and particles with the lattices oriented along the [1 0 0] and [1 1 0] directions were prepared. Hysteresis curves were obtained for particles and reference samples, in the field range ±2T at temperatures between 50 and 300K. The particles were further imaged by magnetic force microscopy. The coercivities of the particles are about the same as that of the reference samples, being of the order of 10mT at room temperature and increasing with decreasing temperature. This may be explained by the temperature dependence of the magnetic anisotropy of the Ni film, estimated to K1=-12.5, -12.8 and -87.6kJm-3 at 295, 250 and 50K, respectively. Whereas the hysteresis curves of the particles are governed by the intrinsic properties of the starting film in low fields, the decreased lateral size influences the behaviour in higher fields as demagnetization effects and features characteristic for annihilation and nucleation of domain walls. One of the samples, rectangles with the long axis along the [1 1 0] direction, has a significantly higher remanence and coercivity than the others. The magnetic images show that the demagnetized state of this sample comprises both single-domain and multidomain particles. Corresponding images showed only multidomain particles in all other samples. Thus it was concluded that the actual size (0.9μm×0.3μm×50nm) is close to the critical size for single domains in Ni.

  • 9.
    Johansson, Christer
    et al.
    RISE, Swedish ICT, Acreo. Chalmers University of Technology, Sweden; University of Gothenburg, Sweden.
    Hanson, Maj
    Chalmers University of Technology, Sweden.
    Hendriksen, Peter Vang
    DTU Technical University of Denmark, Denmark.
    Mörup, Steen
    DTU Technical University of Denmark, Denmark.
    The magnetization of magnetic liquids containing amorphous Fe1-xCx particles1993In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 122, p. 125-128Article in journal (Refereed)
    Abstract [en]

    The magnetization of amorphous Fe1-xCx particles in decalin was measured in magnetic fields up to 12 T at temperatures between 10 and 250 K. For particles with a diameter of 3.2 nm, the zero field cooled magnetization has a maximum at 20 K. This is interpreted as a blocking of the superparamagnetic relaxation of single particles.

  • 10.
    Jonasson, Christian
    et al.
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Schaller, Vincent
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Zeng, Lunjie
    Chalmers University of Technology, Sweden.
    Olsson, Eva
    Chalmers University of Technology, Sweden.
    Frandsen, Cathrine
    DTU Technical University of Denmark, Denmark.
    Castro, Alejandra
    Solve AB, Sweden.
    Nilsson, Lars
    Solve AB, Sweden.
    Bogart, Lara
    University College London, UK.
    Southern, Paul
    University College London, UK.
    Pankhurst, Quentin
    University College London, UK.
    Morales, Puerto
    Institute of Material Science of Madrid, Spain.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Modelling the effect of different core sizes and magnetic interactions inside magnetic nanoparticles on hyperthermia performance2019In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 477, p. 198-202Article in journal (Refereed)
    Abstract [en]

    We present experimental intrinsic loss power (ILP) values, measured at an excitation frequency of 1 MHz and at relatively low field amplitudes of 3.4 to 9.9 kA/m, as a function of the mean core diameter, for selected magnetic nanoparticle (MNP). The mean core sizes ranged from ca. 8 nm to 31 nm. Transmission electron microscopy indicated that those with smaller core sizes (less than ca. 22 nm) were single-core MNPs, while those with larger core sizes (ca. 29 nm to 31 nm) were multi-core MNPs. The ILP data showed a peak at ca. 20 nm. We show here that this behaviour correlates well with the predicted ILP values obtained using either a non-interacting Debye model, or via dynamic Monte-Carlo simulations, the latter including core-core magnetic interactions for the multi-core particles. This alignment of the models is a consequence of the low field amplitudes used. We also present interesting results showing that the core-core interactions affect the ILP value differently depending on the mean core size.

  • 11.
    Ludwig, Frank
    et al.
    Technische Universität Braunschweig, Germany.
    Balceris, Christoph
    Technische Universität Braunschweig, Germany.
    Viereck, Thilo
    Technische Universität Braunschweig, Germany.
    Posth, Oliver
    Physikalisch-Technische Bundesanstalt, Germany.
    Steinhoff, Uwe
    Physikalisch-Technische Bundesanstalt, Germany.
    Gavilan, Helena
    CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Costo, Rocio
    CSIC Instituto de Ciencia de Materiales de Madrid, Spain.
    Zeng, Lunjie
    Chalmers University of Technology, Sweden.
    Olsson, Eva
    Chalmers University of Technology, Sweden.
    Jonasson, Christian
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Size analysis of single-core magnetic nanoparticles2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 427, p. 19-24Article in journal (Refereed)
    Abstract [en]

    Single-core iron-oxide nanoparticles with nominal core diameters of 14 nm and 19 nm were analyzed with a variety of non-magnetic and magnetic analysis techniques, including transmission electron microscopy (TEM), dynamic light scattering (DLS), static magnetization vs. magnetic field (M-H) measurements, ac susceptibility (ACS) and magnetorelaxometry (MRX). From the experimental data, distributions of core and hydrodynamic sizes are derived. Except for TEM where a number-weighted distribution is directly obtained, models have to be applied in order to determine size distributions from the measurand. It was found that the mean core diameters determined from TEM, M-H, ACS and MRX measurements agree well although they are based on different models (Langevin function, Brownian and Néel relaxation times). Especially for the sample with large cores, particle interaction effects come into play, causing agglomerates which were detected in DLS, ACS and MRX measurements. We observed that the number and size of agglomerates can be minimized by sufficiently strong diluting the suspension.

  • 12.
    Prabu, Chakkarapani
    et al.
    Anna University, India.
    Latha, Subbiah
    Anna University, India.
    Selvamani, Palanisamy
    Anna University, India.
    Ahrentorp, Fredrik
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Takeda, Ryoji
    Yokohama National University, Japan.
    Takemura, Yasushi
    Yokohama National University, Japan.
    Ota, Satoshi
    Shizuoka University, Japan.
    Layer-by-layer assembled magnetic prednisolone microcapsules (MPC) for controlled and targeted drug release at rheumatoid arthritic joints2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 427, p. 258-267Article in journal (Refereed)
    Abstract [en]

    We report here in about the formulation and evaluation of Magnetic Prednisolone Microcapsules (MPC) developed in order to improve the therapeutic efficacy relatively at a low dose than the conventional dosage formulations by means of magnetic drug targeting and thus enhancing bioavailability at the arthritic joints. Prednisolone was loaded to poly (sodium 4-styrenesulfonate) (PSS) doped calcium carbonate microspheres confirmed by the decrease in surface area from 97.48 m2/g to 12.05 of m2/g by BET analysis. Adsorption with oppositely charged polyelectrolytes incorporated with iron oxide nanoparticles was confirmed through zeta analysis. Removal of calcium carbonate core yielded MPC with particle size of ~3.48 µm, zeta potential of +29.7 mV was evaluated for its magnetic properties. Functional integrity of MPC was confirmed through FT-IR spectrum. Stability studies were performed at 25 °C±65% relative humidity for 60 days showed no considerable changes. Further the encapsulation efficiency of 63%, loading capacity of 18.2% and drug release of 88.3% for 36 h and its kinetics were also reported. The observed results justify the suitability of MPC for possible applications in the magnetic drug targeting for efficient therapy of rheumatoid arthritis.

  • 13.
    Prieto Astalan, A.
    et al.
    RISE, Swedish ICT, Acreo.
    Jonasson, Christian
    RISE, Swedish ICT, Acreo.
    Petersson, K.
    RISE, Swedish ICT, Acreo.
    Blomgren, J
    RISE, Swedish ICT, Acreo.
    Ilver, Dag
    RISE, Swedish ICT, Acreo.
    Krozer, A.
    RISE, Swedish ICT, Acreo.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Magnetic response of thermally blocked magnetic nanoparticles in a pulsed magnetic field2007In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 311, no 1, p. 166-70Article in journal (Refereed)
    Abstract [en]

    In order to detect fast changes of the Brownian relaxation time due to reaction kinetics on the surface of magnetic particles or particle-clustering processes, we have developed a method that uses pulsed magnetic fields and detects the relaxation of the magnetic response on the time scale of milliseconds. We compared measurements in the frequency domain with the time domain measurement using particle suspensions with three different median sizes. The results obtained with the two methods agreed well. Time domain determination of Brownian relaxation was then used to study the reaction kinetics of the clustering process when sodium chloride solution was added to a magnetic nanoparticle suspension.

  • 14. Schaller, V
    et al.
    Wahnström, G
    Sanz-Velasco, A
    Enoksson, P
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Monte Carlo Simulation of Magnetic Multi-Core Nanoparticles2009In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 321, p. 1400-3Article in journal (Refereed)
  • 15.
    Sriviriyakul, Thana
    et al.
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Bogren, Sara
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Schaller, Vincent
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Jonasson, Christian
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Blomgren, Jakob
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Ahrentorp, Fredrik
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Lopez-Sanchez, Patricia
    RISE - Research Institutes of Sweden, Bioscience and Materials, Agrifood and Bioscience.
    Berta, Marco
    RISE - Research Institutes of Sweden, Bioscience and Materials, Agrifood and Bioscience.
    Grüttner, Cordula
    micromod Partikeltechnologie GmbH, Germany.
    Zeng, Lunjie
    Chalmers University of Technology, Sweden.
    Stading, Mats
    RISE - Research Institutes of Sweden, Bioscience and Materials, Agrifood and Bioscience.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Nanorheological studies of xanthan/water solutions using magnetic nanoparticles2019In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 473, p. 268-271Article in journal (Refereed)
    Abstract [en]

    We show results of nanorheological studies of different concentrations of xanthan (non-Newtonian fluid) in water using magnetic nanoparticles (MNPs) together with the AC susceptibility (ACS) vs frequency method. For comparison we also show the ACS response for different concentrations of glycerol in water (Newtonian fluid). The ACS response is measured, and the data is modelled using dynamic magnetic models and different viscoelastic models. We study the ACS response (in-phase and out-of-phase ACS components) at different concentrations of xanthan in water (up to 1 wt% xanthan) and with a constant concentration of MNPs. We use MNP systems that show Brownian relaxation (sensitive to changes in the environmental properties around the MNPs). ACS measurements are performed using the DynoMag system. The Brownian relaxation of the MNP system peak is shifting down in frequency and the ACS response is broadening and decreases due to changes in the viscoelastic properties around the MNPs in the xanthan solution. The viscosity and the storage moduli are determined at each excitation frequency and compared with traditional macroscopic small amplitude oscillatory shear rheological measurements. The results from the traditional rheological and nanorheological measurements correlate well at higher xanthan concentration.

  • 16.
    Tarras-Wahlberg, N.
    et al.
    University of Gothenburg, Sweden; Chalmers University of Technology, Sweden.
    Kamali, S.
    University of California, USA.
    Andersson, M.
    University of Gothenburg, Sweden; Chalmers University of Technology, Sweden.
    Johansson, Christer
    RISE, Swedish ICT, Acreo.
    Rosen, A.
    University of Gothenburg, Sweden; Chalmers University of Technology, Sweden.
    Magnetization Mössbauer study of partially oxidized iron cluster films deposited on HOPG2014In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 367, p. p40-6Article in journal (Refereed)
    Abstract [en]

    Iron clusters produced in a laser vaporization source were deposited to form cluster-assembled thin films with different thicknesses on highly oriented pyrolytic graphite substrates. The development of oxidation of the clusters with time, up to three years, was investigated by magnetic measurements using an alternating gradient magnetometer. Furthermore, to receive information about the oxidation states, clusters of 57Fe were studied using Mössbauer spectroscopy. The magnetic analysis shows a time evolution of the saturation magnetization, remanence, and coercivity, determined from the hysteresis curves characteristic of a progressing oxidation. The different thicknesses of the iron cluster films as well as a protective layer of vanadium influence the magnetic properties when the samples are subjected to oxidation with time. While the saturation magnetization and remanence decrease and reach half the initial values for almost all the samples after three years, the coercivity increases for all samples and is more substantial for the thickest sample with a vanadium protective layer. This value is three folded after three years. Furthermore, based on a core-shell model and using the saturation magnetization values we have been able to quantitatively calculate the amount of the increase of Fe-oxide as a function of time. The Mössbauer spectroscopy shows peaks corresponding to iron metal and maghemite.

  • 17.
    Witte, Kerstin
    et al.
    University of Rostock, Germany; Micromod Partikeltechnologie GmbH, Germany.
    Müller, Knut
    Micromod Partikeltechnologie GmbH, Germany.
    Grüttner, Cordula
    Micromod Partikeltechnologie GmbH, Germany.
    Westphal, Fritz
    Micromod Partikeltechnologie GmbH, Germany.
    Johansson, Christer
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Particle size- and concentration-dependent separation of magnetic nanoparticles2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 427, p. 320-324Article in journal (Refereed)
    Abstract [en]

    Small magnetic nanoparticles with a narrow size distribution are of great interest for several biomedical applications. When the size of the particles decreases, the magnetic moment of the particles decreases. This leads to a significant increase in the separation time by several orders of magnitude. Therefore, in the present study the separation processes of bionized nanoferrites (BNF) with different sizes and concentrations were investigated with the commercial Sepmag Q system. It was found that an increasing initial particle concentration leads to a reduction of the separation time for large nanoparticles due to the higher probability of building chains. Small nanoparticles showed exactly the opposite behavior with rising particle concentration up to 0.1 mg(Fe)/ml. For higher iron concentrations the separation time remains constant and the measured Z-average decreases in the supernatant at same time intervals. At half separation time a high yield with decreasing hydrodynamic diameter of particles can be obtained using higher initial particle concentrations.

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