The dynamical motion of a pair of microparticles exposed to acoustic standing waves and located at the pressure nodal plane is studied using numerical simulations and experiments. The insight into their dynamical behavior along the pressure nodal plane due to the competition between the axial primary radiation and interparticle forces is elucidated. An expression for axial primary radiation force acting on a particle is derived, and the particle dynamics is simulated using fluid-structure interaction model based on the arbitrary Lagrangian-Eulerian method. Considering the total radiation force acting on a particle is the sum of the axial primary radiation force and the interparticle force, three distinct dynamical regimes are observed depending upon the relative magnitudes of the acoustic forces which in turn depend on the gradient of the acoustic energy density. Acceleration, deceleration, and constant velocity motion of the pair of approaching particles are observed, which are explained by the interplay of the acoustic and non-acoustic forces. The dynamical motion of the pair of particles predicted using the model is in very good agreement with the experimental observations.
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