Understanding the physics of how fluids flow inside a capillary several times thinner than a human hair could help design nanostructures that could possibly play a role in next-generation solar cells and new biomedical applications, according to researchers at the Indian Institute of Science Education and Research (IISER), Pune.
In a recent research paper, the scientists demonstrated that the physical properties of fluids at nanometre lengths do contribute to the process of chemical synthesis through which tiny structures are fabricated. They say that the findings, reported in the May edition of journal Physical Review E, provide scope for further research and may also have implications in emerging biomedical applications of nanotechnology, including drug delivery.
The researchers set up two reagents ? which are substances or compounds that start a chemical reaction ? in separate beakers connected by a bridge that had an aluminium oxide foil with tiny pores. The reagents flowed unevenly to mix through the pores and produced nanotubes of cadmium sulfide, a compound known for its optoelectronic properties. Optoelectronic is the study and application of electronic devices that source, detect and control light.
?What we tried to see is whether size as well as the flow of chemical solutions can also affect nanofabrication. If I do the chemistry inside a confined geometry, how is it going to affect the ultimate product? Does it depend on the nature of flow of chemical solutions?? says IISER Pune assistant professor Shouvik Datta, who co-authored the paper with PhD student Arthur Varghese. ?Our point is that any nanoscale chemical reaction or nanoscale structure formation is not the playground of chemical kinetics alone. The physics of flow of such chemical solutions also play a very crucial role there.?
According to the researchers, the study of nanofluidic flow through confined channels has been widely reported in scientific literature, but the hydrodynamics of two different fluids mixing and reacting in a confined space to produce nanostructures is not well investigated. The experiment indicated certain instability in fluid flow, which, the team says, is contrary to the assumption that fluids flow in a laminar or streamlined fashion in such small lengths.
?Preliminary estimates imply that the usual description of hydrodynamic instabilities cannot account for the onset of such instabilities at the nanoscale. Therefore, all these results and analyses presented here build a strong case for continued experimental investigations as well as theoretical developments in such directions,? the paper notes. ?These are necessary to explore the physical origin of multicomponent reactive fluid flow through nanochannels and also to examine the mechanism of chemohydrodynamic instabilities at the nanoscale in more detail.?
Datta, a semiconductor physicist, embarked on this study with the aim of developing nanostructures fit for use in optoelectronics or photovoltaic devices, such as solar cells. The nanotubes from their experiment also displayed high photoluminescence, which the researchers have discussed in a subsequent paper that has been submitted for publication.
?We are trying to model the structural growth process from a chemo-hydrodynamical perspective and also model the electro-optic property of the nanotubes and then see what the connection is,? says Datta. ?There is an intimate connection between the optical and electronic properties that you see with its structural properties, which obviously depends on the particular growth mechanism.? He adds their next step would be to use these nanotubes in a device and study any improvements in their efficiency.
Nanoscale structures are seen, theoretically, to be useful in achieving higher power conversion efficiency.
?Batteries and solar cells, or photovoltaics, designed using nanostructures have received significant impetus in the last five years and have the potential of making a huge impact,? says Tata Institute of Fundamental Research, Mumbai, faculty member Mandar Deshmukh. An expert from the condensed matter physics and materials science department, Deshmukh added that nanotechnology offers the advantages of cost reduction, chemical routes for synthesis and possibly greater efficiency in converting light into electrical energy. ?However, it remains to be seen if the promise of nanotechnology in these two sub-fields is borne out.?
According to Datta, the simplicity of their method may also be helpful in growing a wide variety of nanowires on a larger scale. ?It doesn?t involve many steps or complicated treatment, it just involves separation of two chemicals with a nanoporous membrane and using that membrane as a nanosized chemical reactor,? he says.