Multiple Particle Tracking (MPT) Measurements of Heterogeneities in Acrylic Thickener Solutions

Abstract

In this study the method of Multiple Particle Tracking (MPT) is used to quantify the degree of structural and mechanical microheterogeneity of two polymeric thickener solutions finally aiming at a better understanding of the contribution of microheterogeneities, which commonly occur in solutions of many synthetic as well as bio‐polymers, on bulk rheology. We have chosen the commercial polyacrylate ester Sterocoll FD and Sterocoll D (BASF Aktiengesellshaft) as model systems. For the Sterocoll FD solution the ensemble‐averaged Mean Square Displacement (MSD) increases almost linearly with time, as expected for such a weakly elastic fluid and relatively similar to that observed for a homogeneous aqueous glycerol solution, used as a reference system. However, the MSD distribution is broader than for the glycerol solution and their statistical analysis clearly reveals a heterogeneous structure on the μm length scale. For the Sterocoll D solution, the average MSD exhibits a subdiffusive behavior, typical for highly elastic solutions. Moreover, the displacements of microspheres at different locations within the solution display a wide range of amplitudes and time dependences. The MSD‐distribution is very broad/bimodal and the statistical analysis indicates a degree of inhomogeneity slightly higher than for the Sterocoll FD solution.