I Congreso de Postgrado fcfm: ingeniería, ciencias e innovación

79 Santiago, 10 al 12 de agosto, 2022 05 F Í S I CA Y A S T ROF Í S I CA FLOW FLUCTUATION IN CONFINED BACTERIAL SUSPENSION Cristian Villalobos C, María Luisa Cordero. Rodrigo Soto Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Avenida Blanco Encalada 2008, Santiago, Chile. Email: cristian.villalobos@ug.uchile.cl ABSTRACT Microswimmersmove the f luid around their bodies, creating f lows that inf luence themovement of other swimmers and particles in the medium. Once the number of microswimmers increases, these hydrodynamic interactions result in a f luctuating f low, which we aim to characterize. In this work, we study experimentally and numerically the f low f luctuations generated by a confined suspension of E.coli bacteria. The suspension is encapsulated in a double emulsion, where an oil droplet gets trapped inside a bacteria-in-oil emulsion. By measuring the mean square displacement (MSD) and the velocity autocorrelation function of the oil droplet, we found that it performs a persistent random walk at short times with a characteristic persistence time τ. Due to the confinement, the MSD reaches a plateau at long times and the velocity correlation function shows a negative peak. We propose a Langevin-type equation with ref lective boundary conditions, where a colored noise termmodels the f low generated by the bacterial suspension and is characterized by two parameters: its amplitude and correlation time. The numerical solution of this model is in good agreement with the experiments and allows us to obtain the characteristic properties of the noise associated with the bacterial bath. ACKNOWLEDGMENTS Funding from ANID through Millennium Nucleus Physics of Active Matter and Beca de Doctorado Nacional 21201766 is gratefully acknowledge.