Theoretical and Computational Studies of Hydrodynamics-based Separation of Particles and Polymers in Microfluidic Channels

Abstract

The advent of microfluidic technology presents many difficulties but also many opportunities for separation science. Leveraging the potential of micro- and nanofluidic geometries is not only a matter of shrinking systems. Miniaturization can shift the relative importance of physical phenomena leading to separation. Theoretical and computational studies into the consequences of miniaturization are vital. Mesoscopic, multi-particle collision dynamics simulations are performed on polyelectrolytes and hard, colloidal solutes. Multiple variations of this simulation algorithm are implemented to achieve versatility for simulating non-equilibrium flows and dispersed solutes. The algorithm is extended to simulate the effects of finite Debye layers on the electro-hydrodynamics of electrophoresing macromolecules and used to study the electrophoresis of charged oligomers, polyelectrolytes and polyampholytes in both free-solution and confined geometries. Multi-particle collision dynamics simulations of hydrodynamic chromatography and field-flow fractionation are also performed to test the predictions of the derived unified, ideal retention theory. This unified, ideal retention predicts the transitions between multiple operational modes, including Faxén-mode FFF. Simulations and the theory show that increases in drag due to hydrodynamic interactions with microfluidic channel walls perturb the retention curves from the ideal predictions at large particle sizes. Further complications to field-flow fractionation including undesirable forces perpendicular to the flow direction, slip at channel walls and rectangular channel geometries are investigated. These theoretical studies lead to the proposal of several novel fractionation techniques, namely adverse-mode FFF, slip-mode FFF and polymer/depletant HC.