LS Instruments

Rethinking Rheology for Complex Materials

For decades, mechanical rheometers have been the standard instruments used to measure the viscoelastic properties of materials. While these techniques provide essential information about the macroscopic response of a material under deformation, they can face limitations when analyzing fragile, or dynamically evolving formulations.

Many modern materials, including polymer solutions, emulsions, creams, gels, and biological formulations, possess complex microstructures that may be altered by the shear forces or large deformations applied during conventional rheological measurements.

To complement classical methods, LS Instruments developed the DWS RheoLab, a rheology platform based on Diffusing Wave Spectroscopy (DWS). By probing the microscopic motion of particles using multiple light scattering, DWS provides access to microstructural dynamics and viscoelastic behavior without mechanically perturbing the sample, offering new insights into the stability and evolution of complex materials.

Optical Rheology: Measuring Microstructure Dynamics

The DWS RheoLab performs microrheology measurements using light scattering to monitor microscopic motion of particles inside complex fluids.

From these microscopic fluctuations, the instrument derives the viscoelastic properties of the material across a wide frequency range.

Unlike classical rheometers, the measurement is:

• contact-free
• non-destructive
• extremely sensitive to microstructure changes

This enables researchers to analyze systems that are difficult or impossible to measure using traditional mechanical rheometers.

Benefits and Applications in R&D Laboratories

As a micro-rheology platform, the DWS RheoLab provides several advantages no matter your specific application:

• G′ and G″ across a very wide frequency range
• Sealed cuvette for no evaporation or contamination
• Very small sample volumes (~0.2–2 mL)
• No mechanical shear applied to the sample
• Continuous in-situ measurement over time
• Go back to your sample for shelf-life studies

The benefits are relevant for different sample types and applications:

Emulsions and Creams

Studying stability and structural evolution in food and cosmetic formulations. Read the article.

Extend the rheological characterization of emulsions. Read the application note.

Polymer Solutions

Access viscoelastic spectra over a very wide frequency range in a single measurement. The Cox–Merz rule allows derivation of 
flow-curve data normally obtained from mechanical rotational instruments. Read the application note.

Gelation Processes

Detect the gel point as G′ crosses G″ without disturbing the forming network. Resolve sol–gel transitions
as a function of temperature, concentration, or time with high resolution. Read the application note.

Microstructure Stability

Track hydrodynamic radius evolution and detect aggregation, coalescence, and Ostwald ripening in real time.
Enables accelerated stability testing at conditions that cannot be measured mechanically. Read the application note.

Optical Rheology: How it works

The DWS RheoLab performs microrheology measurements using light scattering to monitor microscopic motion of particles inside complex materials.

From these microscopic fluctuations, the instrument derives the viscoelastic properties of the material across a wide frequency range.

Based on a non-destructive, contact-free approach, it is ideally suited for soft, fragile materials undergoing microstructural changes. These are difficult to impossible to measure using traditional mechanical rheometers.

DWS and Mechanical Rheometry: complementary tools