Microrheology involves tracking the motion of dispersed tracer particles of known size by Dynamic Light Scattering (DLS) and determining the rheological properties of the sample using the Generalized Stokes-Einstein Relation. DLS Microrheology is a passive microrheology technique, whereby the colloidal probe particles only undergo thermal fluctuations in a system at thermodynamic equilibrium.
DLS Microrheology is applicable for the rheological characterization of low viscosity and weakly-structured complex fluids, such as dilute solutions of polymers and surfactants through to concentrated protein formulations. For these types of materials, Microrheology offers significant advantages:
- Probes very high frequencies necessary for characterizing inherent short timescale, viscoelastic responses (whereas mechanical techniques are fundamentally limited by inertia).
- Only requires microliter-scale volumes for rheological characterization of materials where sample volume is limited e.g. protein-based formulations.
Applications of DLS Microrheology include:
- Rheological characterization of therapeutic proteins and biopolymer solutions.
- Viscoelastic measurements of protein solutions to assess onset of protein-protein interactions and insoluble aggregate formation
- Formulation development and screening.
- High frequency rheology of dilute systems on process-relevant timescales.
- Monitoring structure development in complex fluids with time or temperature, or structure breakdown on dilution.