In recent years, particle hydrodynamic focusing and ordering in a confined microchannel has been developed as a promising technique in lab-on-a-chip systems such as microparticle/cell separation, on-chip flow cytometry and detection. During the focusing, the uniformly distributed finite-sized particles from the channel inlet migrate across streamlines to several equilibrium positions according to the balance between series of hydrodynamic lift forces. While most studies in literature focus on single particle’s motion in the hydrodynamic focusing process by considering particle-liquid interactions, very few of them investigate particle-particle interactions, which is important in particle ordering and manipulation at high throughput. In this study, we use an immersed boundary (IB) - lattice Boltzmann (LB) coupled model to investigate the dynamic behaviors of a particle pair traveling through a square microchannel. The utilized numerical model retains the advantages of both LBM and IBM, which can accurately model the momentum exchange between liquid and particles, and conveniently treat complex geometry and movement of liquid-particle surfaces. By conducting numerical simulations, the time-dependent dynamic behaviors of particle pairs, including trajectories and interactions from initial rest condition to final quasi-equilibrium condition are obtained. Influences of important factors, such as Reynolds number and particle sizes on particles’ motions are discussed and the underlying physical mechanisms of particle-particle interactions are revealed in-depth.

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