| This thesis is focused on the boundary effects (including the size and shape of particles and channel, zeta potentials, applied electric potentials, transient effects and etc.) on the electrophoretic motion of particles in relatively small microchannels filled with electrolyte solutions. Thin electrical double layers are assumed. Theoretical models are developed to describe the steady state and transient electrokinetic particle-liquid flow in microchannels. To solve the theoretical models, three numerical simulation methods are developed and implemented in computer programs. After performing a series of numerical benchmark tests, computer programs are used to study the electrophoretic motion of particles in five different particle-channel systems.; Numerical results show that the electrophoretic velocity of a particle is proportional to its zeta potential. When a sphere or circular cylinder moves along the axis of a circular channel, its electrophoretic velocity decreases with the decrease of channel size. However, when a sphere moves eccentrically in a circular channel with a very small separation distance, its electrophoretic velocity increases with the decrease of channel size. The moving trajectory of a particle in a T-shaped microchannel can be controlled by adjusting the electrical potentials applied at three ends of the channel. The presence of one particle nearby the other one affects the motion of two particles, and this effect weakens with the increment of the separation distance. Numerical simulations show a scenario of a fast-moving particle climbing and surpassing a slow-moving particle.; To validate the numerical simulations, physical experiments are designed and conducted to measure the near-contact electrophoretic motion of spheres in circular capillaries. It is found that numerical results roughly agree with experimental ones. |
