Study On Electroosmotic Flow In Micro-and Nano-fluidics By Numerical Simulation

In the past twenty years, micro-/nano-fludic systems have gained great progress be-cause of development of micromachining and micro-fabrication technologies. With ad-vantages of smallvolume, mass production, high degree of automation and good portabil-ity, micro-/nano-fluidic systems have attracted eye of many researchers, and show goodfuture in field of biology, analytical chemistry, clinic and environment monitoring.Many elements are integrated into micro-/nano-fluidic systems, which usually in-clude micro-pumps, micro-valves, mixing and kinds of devices for connecting and con-trol, resulting in high complexity. Reliability and coordination of the devices are im-portant for the systems to operating. Micro devices for mass transport and fluid control,based on electroosmotic flow (EOF), which dont't have moving parts like mechanicalpumps and valves, eliminate the drawback of traditional mechanical-based micro devicesand show great potential for appplications in micro-/nano-fludic systems.Currently, manufacturing of micro-/nano-fludic system is not a problem, but becausemicro-scale flow is very different from macro-scale flow, the lacking of understanding ofcomplex electrokinetic phenomena makes it difficult to do systematic design and preciseoperation control of micro-/nano-fludic system. So, it is very import to get fundamentalunderstanding of electroosmotic flow for design and operation of micro devices based onelectroosmotic flowMolecular dynamics (MD) simulation is an important tool for studying fluid flowfrom view of particles. For above reasons, MD simulations are performed to study char-acteristics of EOF in direct plate nano-scale channel.Method based on MD simulation for EOF in nano-scale channel are construct withconsidering interactions between solvent molecule (water), charged ions, ions of channelwalls including many-body potentials and Coulomb interactions. A corrected Particle- Mesh Ewald (PME) summation method is used to compute the Coulomb interactions.Moleculemodels,includingchannelwallatoms(diamondlattice),solventmoleculemodel(simple point charge extented model, SPC/ E) and ions models modeled by chargedLennard-Jones atoms, are used. The simulation program are modified from an MDsimualtion package Gromacs.Firstly an MD simulation for EOF in 3.5nm wide channel with only Cl? ions in thesolution is performed. Ion distribution, water distribution and velocity of water across thechannel are studied and reasons are given for phenomena of gathering of ions near thechannel wall, layering of water and ion distribution near the wall.ManyfactorsmayhaveeffectsoncharacteristicsofEOF,forexample, surfacechargedensity, width of channel, external electric field, surrounding temperature etc. A seriesof MD simulation are performed to study effects of ion concentraiton, width of channeland species of ions on nano-scale EOF. For instance, MD simulations of Cl? solutionwith ion mole concentration of 1.304 mol/L, Na+ of 0.625 mol/L, Mg2+ of 0.625 mol/Lrespectively are performed to study effects of species on EOF. Also systems with channelwidth of 1.0 nm and 2.0nm respectively are simulated for studying how channel widtheffects EOF. Results from simulation have coincidence with continuum theory in effectsof ion species and mole concentration but contradictions with prediction of continuumtheory in system with channel with of 1.0 nm.Results of the thesis about EOF may guide the design and manufacturing of microdevices based on EOF for mass transpot and flow control.