Nowadays, the need for nano and mesostructured materials has taken the attention of the scientific community. The creation of such systems has generated new challenges in their design process and characterization.
One of the simplest systems obtained are nanoparticles, which present unique characteristics such as ferromagnetism, in the case of magnetite, maghemite and iron carbide, or catalytic properties as observed with Pt ones. On the other hand, their size distribution, homogeneous composition and morphology remain difficult parameters to control, and in the best cases, the overall dimensions should not exceed the nanometer size.
Recently, there is been a considerably drive in the construction of microscale hierarchically structured materials based on nanoparticles.
A well developed technique for fiber generation is electrospinning. This process consists of the application of an electric field to a capillary containing a polymer solution, held on the tip by its surface tension. As the intensity of the electric field is increased, the hemispherical surface of the solution at the tip extends to form a polarized conical shape known as the Taylor cone. When the electric field reaches a critical value at which the repulsive force overcomes the surface tension force, a jet is ejected. The jet trajectory can be controlled by an electric field and, along its trajectory the solvent evaporates leaving a charged polymer fiber that distributes itself randomly on a collecting metal screen, producing a non-woven fabric. This technique produces fibers ranging from micro to few hundreds of nanometers, by modifying parameters such as solution viscosity and conductivity, electric potential applied, distance of the collecting plate, etc
Scheme 1. Usual experimental set up of electrospinning process.
By combining nanoparticle synthetic methodologies with electrospinning techniques, it is possible to synthesize mesostructured microfibers presenting the same properties as their nanoparticle analogues.
Figure 1. SEM images of electrospun fibers containing Chromium Nitride precursors.