Probing rheological properties using Dynamic Light Scattering
Rheology is the study of flow and deformation of materials. Rheological properties, such as viscosity and viscoelasticity, can be measured from bulk sample deformation using a mechanical rheometer, or on a micro-scale using an optical technique such as Microrheology.
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.
Applications: characterization of nanoparticles, colloids and proteins, protein mobility measurements and microrheology of macromolecules.
Measurement types: particle/molecular size, absolute molecular weight, zeta potential, protein mobility and microrheology.See the Zetasizer Nano ZSP
Applications: characterization of nanoparticles, colloids and proteins.
Measurement types: particle/molecular size, absolute molecular weight, zeta potential and (optional) microrheology.See the Zetasizer Nano ZS
Malvern solutions for Microrheology
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