Manufacturing organic nanoparticles using a self-assembly technique relies on the natural tendency of molecules to aggregate and form larger structures. Due to uniform crystal growth, the shape of these particles is always spherical. While the fabrication of non-spherical particles has been reported previously, the average diameter of these cup structures was in the micron scale.
Scanning electron microscope images of SiO2 cups with PVP (blended silica and polyvinylpyrrolidine solution) concentration. (Source: Texas A&M University)
"We have been working on a new fabrication technique for creating hemi- spherical nanocomposite cups using electrospraying" Jun Kameoka, Assistant Professor in the Electrical Engineering Department at Texas A&M University told Nanowerk. "Cups with diameters as small as 50 nm were fabricated using the above technique. In addition, we have found that the ion concentration of polymer solution would be critical process parameters that can determine the morphology of these cups."
Kameoka's t technique involves
using an electrospray, which evolved from the well known
electrospinning technique, as well as calcination. This
process can provide a very straight forward, highly efficient
and very economical way to fabricate nanoscale composite
structures. An electrostatic field forces the polymer jet from
the electrospray source, and the continuous polymer jet splits
into small individual droplets due to the surface tension of the
solution and the electrostatic force. Then, the individual cups
are formed in transit to the counter electrode. The morphology of the nanocups changed by varying the
ionic concentration of the polymer solution.
This technique is very
simple and highly efficient compared to other nanomaterial
fabrication techniques such as self assembly of nanoparticles.
The researchers also found that the diameter of the silica nanocups
could be controlled by the PVP concentration. The lower
the concentration of the polymer solution, the smaller the
fabricated particles were. In addition, the morphology of the
nanocups changed by adding ions into the polymer–sol–gel
solution. A higher concentration of ions in the PVP solution
resulted in the pore size becoming smaller and the shape
becoming more spherical. These nanostructures may find uses
in medical applications such as drug delivery, cancer treatment
and other products such as cosmetics and dyes.