Molecular Dynamics Simulation of Electroosmotic & Pressure Driven Flows in Nanochannels

The members of the Committee appointed to examine the thesis of MIAO MIAO find it satisfactory and recommend that it be accepted. ___________________________________ Chair ___________________________________ ___________________________________ iii ACKNOLEDGEMENT I would like to thank my advisor Dr. Prashanta Dutta for the research guidance, patience and understanding during the past four years. He has been making a difference of my life ever since the day I took his undergraduate heat transfer class. I am especially grateful for his great emotional and technical support during my internship period at Technip USA. To write a thesis while being a full time engineer is nothing like doing research while being the teaching assistant at school. Without him, this thesis is not possible. I would also like to thank Washington State University for providing me the financial support. Thirdly, many thanks go to my fellow lab mates for their mental support. In the end, I want to give the greatest appreciation to my parents. Chair: Prashanta Dutta In order to deepen our understanding of pressure driven flow and electroosmotic flow in nano channels, a molecular dynamics simulation program was developed. Pressure driven flow happens due to a pressure gradient in the channel, whereas ions' movement due to an external electric field induces electroosmotic flow. For pressure driven flow, Lennard-Jones potential is simply used to simulate the van der Waals interaction. In addition to that, 3D Ewald Summation was employed to simulate the electrostatic interaction in electroosmotic flow. Our system consists of 168 spherical rigid wall molecules and 2048 spherical liquid molecules. Channel length, width and height (L x , L y, L z) are 4.588 nm, 4.588nm and 3.614nm respectively. Water molecules are sandwiched between top and bottom walls with a FCC structure as the initial configuration. In electroosmotic flow, there are 32 ions out of 2048 liquid molecules and 32 wall molecules are assigned charges in order to reach an electrostatic neutral condition. A periodical boundary was added to simulate bulk flow in x and z direction. A Berendsen thermostat is also used to control the system temperature. Verlet neighbor hood list helps to reduce the computation time when calculating the pair interaction of molecules. v Six studies were conducted in this reearch: A comparison test of pressure driven flow with existing continuum theories; a parametric study of effect of external force in pressure driven flow; a limiting case study where the continuum theory completely …