ACTIVE MICRO-RHEOLOGY:LEARNING ABOUT COMPLEX FLUIDS BY PULLING INTRUDERS

Carlos Mejia-Monasterio (Personal webpage)

Rheology is an old and firmly established theory that studies the deformation and flow of matter. With the advent of new imaging technologies and numerical tools, rheological studies at the microscopic scales have gained increasing interest to study the dynamical properties of fluids in low-dimensional or confined geometries. The classical experiment in micro-rheology consists of tracking the motion of a colloidal particle, either due to thermal fluctuations or when it is pulled with a constant force, to infer the properties of the surrounding environment. In this lecture we will discuss the dynamical properties of such pulled intruder in arbitrary dimensions. We will introduce the micro-viscosity in the Stokes regime, when the pulling force is not too large. At larger forces nonlinear contributions cannot be neglected, and we will discover that some of these contributions actually dominate the dynamics of the intruder, leading to anomalous diffusion depending on the effective spatial dimensions.