Executive Summary : | The constrained motion of particles is ubiquitous in ion channels, nanopores, and sub-cellular level processes. The uneven shape of these structures regulates the transport of particles exhibiting peculiar properties. Many biological microorganisms and artificially active particles, while moving in a constrained or free environment, use their environment's free energy to convert it into sustained motion. The processes behind such active motion and the dynamical features of these systems are varied and have been widely investigated. A new field has been emerging in the last few years known as" active matter," which focuses on the physical features of propulsion, processes, and motility-induced emergent collective behavior of a more significant number of identical entities. Various industrial, biomedical, and clinical applications rely on separating and sorting small particles, e.g., waste-water purification, blood sample preparation, and disease diagnosis. Separation techniques in research often hinge on the response of particles to external stimuli such as gradients or fields. The behavior of these particles, whether they drift or diffuse, is influenced by various factors, including mass, size, shape, and charge. It is in high demand for laboratory research and industrial applications to separate mesoscopic particles from mixtures according to their physical properties. We study the diffusive behavior of active particles in confined geometries. This problem is difficult to solve analytically. Thus, we study the problem using numerical modeling and by doing experiments. In the numerical modeling, consider the dynamics of an active Brownian particle suspended in a fluid medium and constrained by a two-dimensional asymmetric channel (varying shapes). An oscillatory force is applied to the particle along the length of the channel. A coupled Langevin equation will be solved to learn the dynamics of the particles in the over-damped regime. Experimentally, the channel shall be placed under the PDMS to attach the inlet and outlets. The setup shall be tested firstly with different-sized (2-20 ?m in diameter) polystyrene particles under different flow rates (10-500 ?l/min using Hamilton's syringe). The polydispersed sample shall flow through Hamilton's syringe in the middle of the channel. Then, the oscillatory force will be employed with closed outlets. The outlets will collect the sample volume that will be further analyzed under the microscope. The process shall repeat for the polydispersed sample to achieve high accuracy in separating particles based on sizes. Secondly, we shall use active particles of a similar size range and flow into the channel to sort the particles. A comparative study between normal Brownian and active Brownian particles will be laid out through this experimental setup. Later, a groove-based asymmetric channel shall be employed to study the effect of obstacles on sorting the mixer of active Brownian particles. |