Adam O'Connell, Ricardo Armenta, Andrea Vaccaro, Peter Schuetz, and Johan Mattsson
University of Leeds, UK
The viscoelastic behaviour of polymer solutions is complex and holds rich insight into the solution dynamics and structure. However, full rheological characterisation typically requires measurements at frequencies far beyond the inertia limit of conventional shear rheometers (~100 Hz). Passive microrheological techniques, for which viscoelastic properties are determined from the thermal motion of dispersed tracer particles, form a powerful toolkit to overcome this limitation. The small size of these particles (~1 micron) means that inertial effects are only significant at extremely high frequencies; thus, the experimentally accessible frequency window can be significantly enhanced. For instance, light scattering techniques, which can measure tracer motion down to very short timescales (~1 nanosecond), allow for rheological characterisation up to ~104 Hz using Dynamic Light Scattering (DLS), and ~106 Hz using Diffusing Wave Spectroscopy (DWS).
In this presentation, the advantage of using microrheological characterisation on polysaccharide solutions will be illustrated for aqueous solutions of locust bean gum (LBG), a high molecular weight polysaccharide of great industrial interest due to its natural origins and strong thickening ability. The frequency-dependent rheological response is obtained over a broad frequency range (1-106 Hz) using a combination of bulk rheology, video particle tracking, DLS, and DWS. Measurements are performed on both aqueous LBG solutions and LBG dissolved in high concentration sucrose solutions, to explore the effects of added sugar.