Investigations on soft materials at nano meter length scales by optical methods

Abstract

The aim of this thesis is to construct a dual optical tweezer setup and use it to investigate the small length scale properties of various soft materials. A dual optical tweezer has been built and then calibrated for measurements of microrheological properties of soft newlinematerials. This setup has been used to investigate the rheology of regenerated silk fibroin solution of Tasar silk. The techniques of microrheology are extended to investigate active suspensions of live bacteria and are developed further, to quantify the antimicrobial action of silver nanoparticles. The emphasis of the studies is then shifted to addressing certain physical aspects of laser tweezers: Asymmetric shaped microscopic newlineobjects show rotations on being optically trapped. These rotations have been newlinecharacterized and experimental results have been modeled by considering effects of hydrodynamics on the rotor. The setup is modified for simultaneous forward and back scattering detection to look at the situation wherein multiple particles are trapped in a single beam tweezer. The modified setup enables one to investigate the bead pair coupling with the optical field.