Proposal Number: CBET-0730026 Principal Investigator: Sohail Murad Institution: University of Illinois Chicago
The objectives of the proposed research are to understand the general details of ion transport and the essential structural and dynamic characteristics for transport of charged particles through a nanochannel under passive, pressure-driven or electric field driven conditions, so as to improve controllability and selectivity. Biological ion channels are themselves nanofluidic devices; however, the level of complexity present in such channels obscures the properties that are the basic essentials of an ion-selective nanochannel. Ion permeation of nanochannels will be studied as a general phenomenon, starting with the simplest model for a nanochannel and increasing the complexity of the model in a stepwise manner by adding attributes that will permit answering some of the questions that are being asked about nanofluidic devices.. Simplified pore models permit investigation of the primary characteristics of a conduction pathway: the shape, radius, and length of the pore, the chemical (hydrophobic or hydrophilic) nature of the pore wall surface, its surface roughness and flexibility, the presence and distribution of surface charges, the presence of an external electric field. Broader Impact: Recent advances in the fabrication of confined fluidic systems such as nanoscale lab-on-a-chip devices and nanofabricated pores raise fundamental questions about ion transport in nanochannels. Solvent slip along the hydrophobic walls of the carbon nanotube is controlled by fluid-wall interactions. Investigation of such slip flow behavior and other characteristics of flow in nanotubes can be vital for generating the high throughput rates required in nanofluidic devices employing carbon nanotubes. In addition similar issues play an important role in transport processes in biological membranes, and cellular functions. This research will provide training for undergraduate and graduate students and will prepare highly skilled technical personnel with broad knowledge encompassing engineering, chemistry, biology, and nanotechnology. The PIs have been actively participating in the WISEST (Women in Science and Engineering System Transformation) program at UIC and will continue those activities through this grant.
The major goal of the project was to understand the permeation of water and ions in membranes. These processes are very important in sustaining life and a better understanding of these processes will also lead to improvement in related separation processes including water desalination, gas separations, ion exchanges etc. Our research clarified many unresolved issues related to transport of ions in membranes. For example it was not well understood why some channels would allow larger ions like potassium to enter while smaller ions like sodium could not. Our research showed that permeation was strongly influenced by how rigid a hydration shell of an ion was. For sodium the shell is very rigid while for potassium it is quite flexible. We also showed that if drugs encapsulated in nanoparticles are used as a delivery mechanism, the designer need to consider the possibility, that these nanoparticles will form temporary nano-channels in membranes, which could allow undesirable transport of water and other ions resulting in cytoxicity. In addition these nanoparticles could also irreversibly damage membranes by transporting molecules from one leaflet of the membrane to another which can sometimes be highly undesirable. Finally while this was not the original focus of our work, our research showed that the structure of membranes can have a significant impact on the interfacial heat resistance of the solid-liquid boundary. Thus we were able to show that changing the behavior of the solid-liquid interface could be profitably used to enable thermal rectification. Thermal rectification can for example result in allowing heat to enter a house during the day when the sun is shining, and prevent it from leaving the house at night when it is much colder outside. In addition this also pointed to a conceptual design for a thermal transistor that could work on waste heat. Waste heat is often available, especially in industrial environments. Waste electricity on the other hand is never an option.
