| 1. |
- Martchenko, Ilya, et al.
(författare)
-
Anisotropic magnetic particles in a magnetic field
- 2016
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 12:42, s. 8755-8767
-
Tidskriftsartikel (refereegranskat)abstract
- We characterize the structural properties of magnetic ellipsoidal hematite colloids with an aspect ratio ρ ≈ 2.3 using a combination of small-angle X-ray scattering and computer simulations. The evolution of the phase diagram with packing fraction φ and the strength of an applied magnetic field B is described, and the coupling between orientational order of magnetic ellipsoids and the bulk magnetic behavior of their suspension addressed. We establish quantitative structural criteria for the different phase and arrest transitions and map distinct isotropic, polarized non-nematic, and nematic phases over an extended range in the φ-B coordinates. We show that upon a rotational arrest of the ellipsoids around φ = 0.59, the bulk magnetic behavior of their suspension switches from superparamagnetic to ordered weakly ferromagnetic. If densely packed and arrested, these magnetic particles thus provide persisting remanent magnetization of the suspension. By exploring structural and magnetic properties together, we extend the often used colloid-atom analogy to the case of magnetic spins.
|
|
| 2. |
- Balashova, Anna, et al.
(författare)
-
New tephrostratigraphic data from Lake Emakat (northern Tanzania) : Implications for the eruptive history of the Oldoinyo Lengai volcano
- 2018
-
Ingår i: Journal of African Earth Sciences. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1464-343X .- 1879-1956. ; 147, s. 374-382
-
Tidskriftsartikel (refereegranskat)abstract
- The northern Tanzanian sector of the Gregory Rift is an area of an active continental rifting, in which sedimentation processes are strongly affected by volcanism. Due to limited stratigraphic exposure, the volcanic record of the region is rather sparse, and assigning volcanic centres for the individual eruptions is difficult. This study presents new data on the tephrostratigraphy of the sedimentary sequence of Lake Emakat, Empakaai Crater, northern Tanzania. Seven volcanic ash layers are identified and described from a 1.1-m core of lake sediments. Geochemical, mineralogical, petrographic and magnetic analyses show that: (1) all ash layers are products of highly explosive eruptions of melilite-bearing magmas; (2) most of the eruptions originate from a complex magmatic system; (3) all ash horizons are very well preserved in the lake environment; and (4) there are significant fluctuations of the bulk magnetic susceptibility of the lacustrine sediments which is related to microtephra from additional eruptions, the result of detritus, washed from the shore during periods of strong lake level fluctuations or periods of high erosion rates, or simply by the contamination by the material from the ash layers. Based on geochemistry and mineralogy of the seven identified ash layers in Lake Emakat, combined with the eruption ages from C-14 datings, we can pinpoint Oldoinyo Lengai volcano as the source of these specific layers. The combination of this new data with existing chronological data from Ryner et al. (2007), retrieved from the same core, provides precise ages of the voluminous highly explosive eruptions in this region of East Africa during the Pleistocene-Holocene transition.
|
|
| 3. |
- Crassous, Jerome, et al.
(författare)
-
Advanced multiresponsive comploids: from design to possible applications.
- 2014
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 6:15, s. 8726-8735
-
Tidskriftsartikel (refereegranskat)abstract
- We extend the commonly used synthesis strategies for responsive microgels to the design of novel multiresponsive and multifunctional nanoparticles that combine inorganic magnetic, metallic/catalytic and thermoresponsive organic moieties. Magnetic responsiveness is implemented through the integration of silica-coated maghemite nanoparticles into fluorescently labeled crosslinked poly(N-isopropylmethacrylamide) microgels. These particles are then employed as templates for the in situ reduction of catalytically active gold nanoparticles. In order to tune the reactivity of the catalyst through a thermally controlled barrier, an additional layer of crosslinked poly(N-isopropylacrylamide) is added in the final step. We subsequently demonstrate that these particles can be employed as smart catalysts. We show that the thermoresponsive nature of the outer particle shell not only provides control over the catalytic activity, but when combined with a magnetic core allows for very efficient removal of the catalytic system through temperature-controlled reversible coagulation and subsequent magnetophoresis in an applied magnetic field gradient. We finally discuss the use of this design principle for the synthesis of complex hybrid particles for various applications that would all profit from their multiresponsive and multifunctional nature.
|
|
| 4. |
- Hirt, Ann M., et al.
(författare)
-
Effect of size, composition, and morphology on magnetic performance : First-order reversal curves evaluation of iron oxide nanoparticles
- 2014
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:4
-
Tidskriftsartikel (refereegranskat)abstract
- Superparamagnetic nanoparticles are employed in a broad range of applications that demand detailed magnetic characterization for superior performance, e. g., in drug delivery or cancer treatment. Magnetic hysteresis measurements provide information on saturation magnetization and coercive force for bulk material but can be equivocal for particles having a broad size distribution. Here, first-order reversal curves (FORCs) are used to evaluate the effective magnetic particle size and interaction between equally sized magnetic iron oxide (Fe2O3) nanoparticles with three different morphologies: (i) pure Fe2O3, (ii) Janus-like, and (iii) core/shell Fe2O3/SiO2 synthesized using flame technology. By characterizing the distribution in coercive force and interaction field from the FORC diagrams, we find that the presence of SiO2 in the core/shell structures significantly reduces the average coercive force in comparison to the Janus-like Fe2O3/SiO2 and pure Fe2O3 particles. This is attributed to the reduction in the dipolar interaction between particles, which in turn reduces the effective magnetic particle size. Hence, FORC analysis allows for a finer distinction between equally sized Fe2O3 particles with similar magnetic hysteresis curves that can significantly influence the final nanoparticle performance. (C) 2014 AIP Publishing LLC.
|
|
| 5. |
- Malik, Vikash, et al.
(författare)
-
Hybrid magnetic iron oxide nanoparticles with tunable field-directed self-assembly
- 2017
-
Ingår i: Nanoscale. - 2040-3364. ; 9:38, s. 14405-14413
-
Tidskriftsartikel (refereegranskat)abstract
- We describe the synthesis of hybrid magnetic ellipsoidal nanoparticles that consist of a mixture of two different iron oxide phases, hematite (α-Fe2O3) and maghemite (γ-Fe2O3), and characterize their magnetic field-driven self-assembly. We demonstrate that the relative amount of the two phases can be adjusted in a continuous way by varying the reaction time during the synthesis, leading to strongly varying magnetic properties of the particles. Not only does the saturation magnetization increase dramatically as the composition of the spindles changes from hematite to maghemite, but also the direction of the induced magnetic moment changes from being parallel to the short axis of the spindle to being perpendicular to it. The magnetic dipolar interaction between the particles can be further tuned by adding a screening silica shell. Small-angle X-ray scattering (SAXS) experiments reveal that at high magnetic field, magnetic dipole–dipole interaction forces the silica coated particles to self-assemble into a distorted hexagonal crystal structure at high maghemite content. However, in the case of uncoated maghemite particles, the crystal structure is not very prominent. We interpret this as a consequence of the strong dipolar interaction between uncoated spindles that then become arrested during field-induced self-assembly into a structure riddled with defects.
|
|
| 6. |
- Sotiriou, Georgios A., et al.
(författare)
-
Hybrid, Silica-Coated, Janus-Like Plasmonic-Magnetic Nanoparticles
- 2011
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 23:7, s. 1985-1992
-
Tidskriftsartikel (refereegranskat)abstract
- Hybrid plasmonic-magnetic nanoparticles possess properties that are attractive in bioimaging, targeted drug delivery, in vivo diagnosis, and therapy. The stability and toxicity, however, of such nanoparticles challenge their safe use today. Here, biocompatible, SiO(2)-coated, Janus-like Ag/Fe(2)O(3) nanoparticles are prepared by one-step, scalable flame aerosol technology. A nanothin SiO(2) shell around these multifunctional nanoparticles leaves intact their morphology and magnetic and plasmonic properties but minimizes the release of toxic Ag(+) ions from the nanosilver surface and its direct contact with live cells. Furthermore, this silica shell hinders flocculation and allows for easy dispersion of such nanoparticles in aqueous and biological buffer (PBS) solutions without any extra fiinctionalization step. As a result, these hybrid particles exhibited no cytotoxicity during bioimaging and remained stable in suspension with no signs of agglomeration and sedimentation or settling. Their performance as biomarkers was explored by selectively binding them with live tagged Raji and HeLa cells enabling their detection under dark-field illumination. Therefore, these SiO(2)-coated Ag/Fe(2)O(3) nanoparticles do not exhibit the limiting physical properties of each individual component but retain their desired functionalities facilitating thus, the safe use of such hybrid nanoparticles in bioapplications.
|
|
| 7. |
- Sotiriou, Georgios A., et al.
(författare)
-
Thermal Energy Dissipation by SiO2-Coated Plasmonic-Superpararnagnetic Nanoparticles in Alternating Magnetic Fields
- 2013
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 25:22, s. 4603-4612
-
Tidskriftsartikel (refereegranskat)abstract
- Multifunctional nanoparticles show great potential in the biomedical field and may help the diagnosis and therapy of diseases. Superparamagnetic nanoparticles are especially attractive because of their ability to dissipate thermal energy in an alternating magnetic field. Furthermore, plasmonic nanoparticles can be effectively used in non- or minimally invasive therapy of tumors exploiting their plasmonic photothermal effect. Here, hybrid plasmonicmagnetic Ag/Fe2O3 nanoparticles are made by flame aerosol technology. These nanoparticles can be in situ encapsulated with an amorphous nanothin SiO2 film to facilitate their dispersion and block any toxicity from Ag/Fe2O3. Detailed physicochemical characterization, including electron microscopy, electron dispersive X-ray spectroscopy, and X-ray diffraction, is performed. Furthermore, their magnetic properties are characterized in detail by monitoring their hysteresis, first-order-reversal-curves, and isothermal remanent magnetization. Finally, the effect of SiO2 and Agcontent on the specific absorption rate (SAR) of the hybrid Ag/Fe2O3 nanoparticles is investigated. The obtained understanding will help the rational design and engineering of multifunctional hybrid nanoprobes targeting specific biomedical applications.
|
|
| 8. |
- Teleki, Alexandra, et al.
(författare)
-
Highly scalable production of uniformly-coated superparamagnetic nanoparticles for triggered drug release from alginate hydrogels
- 2016
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:26, s. 21503-21510
-
Tidskriftsartikel (refereegranskat)abstract
- Intelligent, on-demand drug administration systems with controlled release kinetics may revolutionize the way diseases are treated. Typically, the release of the therapeutic payload from these systems is activated by stimuli-responsive nanofillers. However, limitations regarding large-scale nanomaterial production and poor reproducibility keep such systems in the labs and away from clinics. Here, we demonstrate the highly scalable and reproducible synthesis of uniform superparamagnetic Fe2O3 nanoparticles coated with a nanothin layer of amorphous SiO2, and evaluate their suitability as stimuli-responsive nanofillers in a drug-loaded biopolymer alginate matrix. The superior colloidal stability of the SiO2-coated Fe2O3 nanoparticles over their uncoated counterparts and their dispersibility in aqueous suspensions facilitates their incorporation in alginate hydrogel microbeads. We examine the hyperthermia performance of such multiscale particle structures in the presence of alternating magnetic fields and compare the release of dextran (a model biomolecule) in the presence and absence of external stimuli. The enhanced triggered release of dextran in the presence of magnetic fields further highlights the potential of such superparamagnetic SiO2-coated Fe2O3 nanoparticles as a functional transducer in such systems.
|
|
