"A STUDY OF QUANTUM ISOTOPIC SIEVING THORUGH CARBON NANOTUBES"

The theory of molecular sieving has long been a subject of importance because of its widespread technological applications .Classical molecular sieving mainly de- pends on the size and shape of the guest molecules and the size of the host solid. However,isotope seperation is usually very difficult to achieve through classical sieving, as the isotopes generally have the same shape and size and differ only in mass.One way to resolve such an issue is through the applications of quantum effects which are prominent inside nanotubes and nanopores of diameters that are comparable with the De-broglie wavelength λ of the molecules. In the recent past, various authors have calculated the selectivity of isotopes (mainly hydrogen-deuterium) diffusing through nanotubes where they predict the preferable selectivity of the heavier species over the lighter species based on the difference in their zero point energies. The effects are more pronounced at low temperature regimes where quantum effects are dominant. However, this kind of sieving, though showing appreciable preference to the heavier isotope, is far from being ”perfect” and also technologically expensive as very low temperature range is required. In our work, we try to search for a technologically inexpensive method for realising isotope sieving by introducing two nanotubes of different radii that are coupled together. Through a mathemetical model that best describes the situation, we try to search for a ”perfect” sieving of the hydrogen-deuterium isotopes over a wide temeperature range, not restricting ourselves to very low temperatures. As we have found out and will be described in the following work,the two nanotube sys- tem does indeed go a long way towards a technologically efficient way of realising ”perfect” sieving. We also employ MD simulations to investigate kinetic sieving of isotopes through nanotubes. The quantum effects are introduced into the system via a modified FH potential, and ring polymer MD simulation is used to model the system. Though the selectivity values we found in our results are lower in comparison to those already predicted using equilibrium sieving, our results show similar qualitative behaviour to the same approach adopted by others previously using different sieving material