Out-of-equilibrium microrheology using optical tweezers to probe directional viscoelastic properties under shear
Department of Physics, Indian Institute of Science - Bangalore, 560012, India
Accepted: 28 October 2010
Many wormlike micellar systems exhibit appreciable shear thinning due to shear-induced alignment. As the micelles get aligned introducing directionality in the system, the viscoelastic properties are no longer expected to be isotropic. An optical-tweezers–based active microrheology technique enables us to probe the out-of-equilibrium rheological properties of a wormlike micellar system simultaneously along two orthogonal directions —parallel to the applied shear, as well as perpendicular to it. While the displacements of a trapped bead in response to active drag force carry signature of conventional shear thinning, its spontaneous position fluctuations along the perpendicular direction manifest an orthogonal shear thickening, an effect hitherto unobserved.
PACS: 87.80.Cc – Optical trapping / 83.60.Fg – Shear rate dependent viscosity / 87.15.N- – Properties of solutions of macromolecules
© EPLA, 2010