Investigating Non Equilibrium Steady State Hydrodynamics Using Optical Tweezers

Paul, Shuvojit (2014) Investigating Non Equilibrium Steady State Hydrodynamics Using Optical Tweezers. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Shuvojit Paul) Shuvojit_Paul-12IP006.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

Hydrodynamics in the micro-scale has fascinating manifestations and is the basis of life itself.Predictions and manipulations of the motion of living or non living mesoscopic particles in uids is thus a challenging area of re- search.Optical tweezers o�er the possibility of probing hydrodynamics in the micro-scale by studying the motion of micron-sized probes that can be con- trollably con�ned in the tweezers (or trap).There is considerable interesting and important work on hydrodynamic interactions that is being performed by researchers all over the world which made me interested in research in this area. Hydrodynamic interactions held understand the prop- erties of colloidal particles, the motion of bacteria in viscous mediums, or even the environment of a cell.Predictions over bacterial or viral motion can lead medical science positively.We are trying to see the true response of a trapped bead and to understand all of the characteristics of that re- sponse.The movement of the trapped particle makes exciting ow �elds sur- rounding it depending on the shape, size, and the manner of movement of the bead.This ow also depends on the surrounding environment and boundaries of the moving particle.Another particle of arbitrary shape responses seeing this ow depending on the di�erent parameters of it. If an optically trapped micro bead is driven by a periodic force, then it experiences a phase lag in its response, which depends on the frequency of the driving signal, the viscosity of the medium, the trap sti�ness and on the size and shape of the trapped particle. My theoretical calculation and experimental results show that the phase di�erence at maximum can be ninety degree.The amplitude of the sig- nal also varies with the signal frequency .The viscosity of the viscous medium in which the particle is trapped increases near a wall.We were trying to see how it e�ects the movement of our trapped beads and we saw its e�ect on the di�usion coe�cient.We are also attempting to extend the understanding to a two-bead system, where one bead is driven and the response of the other is measured. The coupling between the beads is purely hydrodynamic, and would lead to a thorough characterization of the hydrodynamic interaction between the beads.

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