Empirical Nanotube Model: Applications to Water Channels and Nano-Oscillators

Carbon nanotubes are building blocks of the fast-developing nanotechnology that leads to revolutionary breakthroughs in material science and engineering. The extraordinary mechanical, electrical, and optical properties of nanotubes combined with novel design concepts enable a variety of applications including high-strength materials, logic circuit units, field emission devices, and hydrogen storage media. In particular, nanobiotechnology, a synergy of nanotechnology and biology, aims at characterizing, building, and utilizing nano-devices to benefit human health as well as employ life forms for technical purposes. Examples are nanotube-based biosensors and drug delivery devices. However, development of the principles in this multi-disciplinary field is still in its infancy. Joint efforts from physics, chemistry, and biology are required to achieve new insights. To this end, an empirical carbon nanotube model is developed in this thesis to describe the interaction between nanotubes and the biological environment. Special emphasis is placed on an accurate and efficient description of the electrostatics of nanotubes, which plays a key role in determining molecular transport dynamics through nanotubes. In the proposed model, atomic partial charges are calculated from a quantum chemistry approach, and the polarizability of the nanotube is modeled through a self-consistent tight-binding method. The suitability of the model is demonstrated through studies of a nanotube water channel and a K+-nanotube complex. It is found in the former case that atomic partial charges on the tube edges greatly contribute to the total interaction energy, while the polarization of the nanotube lowers the electrostatic energy once a water molecule moves inside the nanotube. In the latter case, quantum mechanics/molecular mechanics simulations reveal that a K+ ion induces a strong dielectric response in the nanotube wall, which helps to trap the ion inside the tube and force the ion to oscillate at a terahertz frequency. Such a nano-oscillator may hold potential applications as a room temperature terahertz wave detector.U of I Onlythesis/dissertatio