Rheo-NMR Spectroscopy

Abstract

Rheology, the science of deformation and flow, is of practical importance for the preparation, processing or application of different materials such as plastics, paints, detergents, oil or food [1]. Besides this practical importance, there is a fundamental interest in understanding rheological phenomena, in particular, those of complex fluids [2]. Different types of complex fluids, for instance, polymer melts and solutions, micellar systems, and solutions of colloidal particles share the common feature of having a mesoscopic length, given by the size of macromolecules, aggregates, particles or superstructures, which is intermediate between the molecular and macroscopic scale [3]. Connected with this mesoscopic length scale is a characteristic relaxation time that is long enough to be important on the time scale of rheological experiments, defined, for example, by the shear rate. For a simple liquid of small molecules, which tumble on the time scale of 10−12 s, the application of shear at a rate of several hundreds or even thousands of s−1 is a slow disturbance not affecting the molecules, the fluid is made of. In this case Newtonian flow is observed. In complex fluids, however, the longest relaxation times can be several seconds and longer so that a shear rate of lower than 10 s−1 brings the experimental time scale and the intrinsic time scale of the system to match. In this case the rheology often becomes nonlinear [4].