ABSTRACT
Amorphous Fe77Cu1Si13B9 ribbons were treated with pulsed laser interference heating (PLIH). The research results will significantly contribute to a better understanding of the impact of PLIH on crystallisation and magnetic properties in precisely defined micro-areas of Fe77Cu1Si13B9 (FeCuSiB) ribbons, which has not yet been described in the literature. It was confirmed here that the use of the laser heating process allowed for the achievement of two-dimensional crystallised micro-areas, periodically distributed (at a distance of 17 µm) on the surface of the amorphous ribbons. The correlation between structural changes (SEM, TEM, HRTEM) and the distribution of magnetic field lines of heated amorphous Fe77Cu1Si13B9 ribbons is presented. Particular attention is paid to structural changes in micro-areas where, by controlling the laser interference heating process, the partial crystallisation of amorphous alloys and the formation of clusters or single nanocrystallites (α-Fe(Si)) embedded in an amorphous matrix occur. The addition of copper to the FeSiB alloy promoted the inhibition of grain growth. Electron holography of micro-areas confirmed shifts in the magnetic field lines in the areas of nanocrystallites, the presence of which in the structure caused the magnetisation of the surrounding amorphous matrix.
ABSTRACT
This paper reports the characterization of iron oxide magnetic nanoparticles obtained via the thermal decomposition of an organometallic precursor, which were then loaded into nanocapsules prepared via the emulsification process in the presence of an amphiphilic derivative of chitosan. The applied synthetic method led to the formation of a hydrophobic layer on the surface of nanoparticles that enabled their loading in the hydrophobic liquid inside of the polymer-based capsules. The average diameter of nanoparticles was determined to be equal to 15 nm, and they were thoroughly characterized using X-ray diffraction (XRD), magnetometry, and Mössbauer spectroscopy. A core-shell structure consisting of a wüstite core and maghemite-like shell was revealed, resulting in an exchange bias effect and a considerable magnetocrystalline anisotropy at low temperatures and a superparamagnetic behavior at room temperature. Importantly, superparamagnetic behavior was observed for the aqueous dispersion of the nanocapsules loaded with the superparamagnetic nanoparticles, and the dispersion was shown to be very stable (at least 48 weeks). The results were analyzed and discussed with respect to the potential future applications of these nanoparticles and nanocapsules based on biopolymers as platforms designed for the magnetically navigated transport of encapsulated hydrophobic substances.
ABSTRACT
Polymer core-shell nanocapsules with magnetic nanoparticles embedded in their oil cores were fabricated and applied as nano(photo)reactors. Superparamagnetic iron oxide nanoparticles (SPIONs) coated with oleic acid were first synthesized and characterized structurally, and their magnetic properties were determined. The capsules with chitosan-based shells were then formed in a one-step process by sonication-assisted mixing of (1) an aqueous solution of the hydrophobically derived chitosan and (2) oleic acid containing the dispersed SPIONs. In this way, magnetic capsules with a diameter of approximately 500-600 nm containing encapsulated SPIONs with an average diameter of approximately 20-30 nm were formed as revealed by dynamic light scattering and scanning transmission electron microscopy measurements. The composition and magnetic properties of the formed capsules were also followed using dynamic light scattering, electron microscopies, and magnetic force microscopy. The water-dispersible capsules, thanks to their magnetic properties, were then navigated in a static magnetic field gradient and transferred between the water and oil phases, as evidenced by fluorescence microscopy. In this way, the capsules could be loaded in a controlled way with a hydrophobic reactant, perylene, which was later photooxidized upon transferring the capsules to the aqueous phase. The capsules were shown to serve as robust reloadable nanoreactors/nanocontainers that via magnetic navigation can be transferred between immiscible phases without disruption. These features make them promising reusable systems not only for loading and carrying lipophilic actives, conducting useful reactions in the confined environment of the capsules, but also for magnetically separating and guiding the encapsulated active molecules to the site of action.
ABSTRACT
Polyetheretherketone (PEEK) coatings of 70-90µm thick were electrophoretically deposited from a suspension of PEEK powder in ethanol on near-ß Ti-13Nb-13Zr titanium alloy. In order to produce good quality coatings, the composition of the suspension (pH) and optimized deposition parameters (applied voltage and time) were experimentally selected. The as-deposited coatings exhibited the uniform distribution of PEEK powders on the substrate. The subsequent annealing at a temperature above the PEEK melting point enabled homogeneous, semi-crystalline coatings with spherulitic morphology to be produced. A micro-scratch test showed that the coatings exhibited very good adhesion to the titanium alloy substrate. Coating delamination was not observed even up to a maximal load of 30N. The PEEK coatings significantly improved the tribological properties of the Ti-13Nb-13Zr alloy. The coefficient of friction was reduced from 0.55 for an uncoated alloy to 0.40 and 0.12 for a coated alloy in a dry sliding and sliding in Ringer's solution, respectively. The PEEK coatings exhibited excellent wear resistance in both contact conditions. Their wear rate was more than 200 times smaller compared with the wear rate of the uncoated Ti-13Nb-13Zr alloy. The obtained results indicate that electrophoretically deposited PEEK coatings on the near-ß titanium alloy exhibit very useful properties for their prospective tribological applications in medicine.
