The search for new antimicrobial substances has increased in recent years. Antimicrobial nanostructures are one of the most promising alternatives. In this work, titanium dioxide nanotubes were obtained by an atomic layer deposition (ALD) process over electrospun polyvinyl alcohol nanofibers (PVN) at different temperatures with the purpose of obtaining antimicrobial nanostructures with a high specific area. Electrospinning and ALD parameters were studied in order to obtain PVN with smallest diameter and highest deposition rate, respectively. Chamber temperature was a key factor during ALD process and an appropriate titanium dioxide deposition performance was achieved at 200 °C. Subsequently, thermal and morphological analysis by SEM and TEM microscopies revealed hollow nanotubes were obtained after calcination process at 600 °C. This temperature allowed complete polymer removal and influenced the resulting anatase crystallographic structure of titanium dioxide that positively affected their antimicrobial activities. X-ray analysis confirmed the change of titanium dioxide crystallographic structure from amorphous phase of deposited PVN to anatase crystalline structure of nanotubes. These new nanostructures with very large surface areas resulted in interesting antimicrobial properties against Gram-positive and Gram-negative bacteria. Titanium dioxide nanotubes presented the highest activity against Escherichia coli with 5 log cycles reduction at 200 μg/mL concentration.

Electrospun nanofibers of poly (vinyl alcohol) (PV) were obtained to improve dispersion of cellulose nanocrystals (CNC) within hydrophobic biopolymeric matrices, such as poly(lactic acid) (PLA). Electrospun nanofibers (PV/CNC)_n were successfully obtained with a final concentration of 23% (w/w) of CNC. Morphological, structural and thermal properties of developed CNC and electrospun nanofibers were characterized. X-ray diffraction and thermal analysis revealed that the crystallinity of PV was reduced by the electrospinning process, and the incorporation of CNC increased the thermal stability of biodegradable nanofibers. Interactions between CNC and PV polymer also enhanced the thermal stability of CNC and improved the dispersion of CNC within the PLA matrix. PLA materials with CNC lyophilized were also casted in order to compare the properties with materials based on CNC containing nanofibers. Nanofibers and CNC were incorporated into PLA at three concentrations: 0.5%, 1% and 3% (CNC respect to polymer weight) and nanocomposites were fully characterized. Overall, nanofibers containing CNC positively modified the physical properties of PLA materials, such as the crystallinity degree of PLA which was greatly enhanced. Specifically, materials with 1% nanofiber 1PLA(PV/CNC)_n presented highest improvements related to mechanical and barrier properties; elongation at break was enhanced almost four times and the permeation of oxygen was reduced by approximately 30%.

The high frequency dynamic behaviors of magnetic nanorings with variable anisotropy along their radius have been studied using micromagnetic simulations. The dynamic susceptibility spectrum and spatial localization of the ferromagnetic resonance modes are investigated by varying anisotropy gradients in nanorings of 200 nm of external radius, with different internal radii. Both the resonant frequencies and the number of peaks depend on the lower energy magnetization configuration which in turn is a function of anisotropy gradients. Besides, it is shown that the effects of the anisotropy gradient are relevant even for the narrowest ring of 10 nm wide. The idea of controlling frequencies by modifying the anisotropy gradients of the system suggests the possibility of using these nanostructures in potential magnetic controllable frequency devices.

Magnetic films of magnetite (Fe₃O₄) with controlled defects, so-called antidot arrays, were synthesized by a new technique called AFIR. AFIR consists of the deposition of a thin film by atomic layer deposition, the generation of square and hexagonal arrays of holes using focused ion beam milling, and the subsequent thermal reduction of the antidot arrays. Magnetic characterizations were carried out by magneto-optic Kerr effect measurements, showing the enhancement of the coercivity for the antidot arrays. AFIR opens a new route to manufacture ordered antidot arrays of magnetic oxides with variable lattice parameters.

We have investigated the magnetostatic interactions between wire-tube nanostructures. We have observed that the coercivity of the array decreases when the distance between the nanostructures decreases. Besides, when the external magnetic field is applied along the axis of the nanostructures, the two Barkhausen jumps observed for an isolated wire-tube nanostructure give rise to several minor jumps for a weakly interacting array, which eventually become a single jump for the most interacting case. Additionally, the angle θ at which maximum coercivity is obtained varies as a function of the center-to-center distance between the nanostructures, while those remanences obtained for arrays with different distances between the nanostructures coincide. In this way, the study of magnetostatic interactions between wire-tube nanostructures is an interesting topic of research in connection with potential applications where it is usually desirable to avoid such interactions or at least control them.