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Bulk rheology

Non-contact analysis of viscoelastic properties

Analyzing viscoelasticity of complex formulations in a non-destructive manner offers a better understanding of network and structure of the product. Classical methods of viscosity determination require to apply a stress to the system, this may cause a perturbation of the network and thus non-representative analysis of the actual structure.

Using a non-contact, optical method (based on MS-DWS) allows measuring bulk rheology  (viscosity & elasticity evolution) without any mechanical stress. The measurement is performed at rest, allowing structure evolution (gelation, rheology aging, or sample stability) to be monitored. A closed glass cell prevents any evaporation or drying and makes it safe to operate at all time.

Key benefits

  • Measurement at rest (no mechanical stress)
  • Viscoelastic properties vs. time
  • Easy sample handling and data treatment

How does it work?

RHEOLASER product range uses MS-DWS (Multi-Speckle Diffusing Wave Spectroscopy) to monitor particle mobility. The technique consists of sending a laser beam into the sample and detecting speckle pattern created by scattered waves. Brownian motion depends on the viscoelastic structure of the sample (it characterizes speedand distance the particle are free to explore). A thorough analysis of scattered waves provides information about the rheological properties of the structure. In a strong gel (viscoelastic systems) particle mobility will be partially limited by the network structure. While in a simple viscous media, the mean square displacement (MSD) will have more linear form.

Monitoring MSD over or and temperature allows to follow gel formation, determine sol-gel transitions and determine gel strength with extreme accuracy and without any contact with the sample.

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Data and key features

> Mean Square Displacement (MSD)

The Mean Square Displacement is the average distance travelled by the particles in the media (unit: nm2). This value grows linearly with time in a purely Newtonian sample, while there is a plateau in a visco-elastic fluid.

When the plateau is getting lower (shorter distance), the elasticity in the product is higher (tighter network), while if the curves get longer (longer times), the viscosity in the product is higher.

Rheolaser MASTER enables the acquisition of MSD curves as a function of time or temperature, allowing to monitor stability, or gelling process...

> Time cure superposition (TCS)

Acquisition of particle MSD as a function of the gel variable enables any sol-gel process to be momnitored. A rescaling process (Time Cure Superposition) can then be applied to determine gel point and gel strength with a great accuracy.

Any kind of gelling process can be studied, no matter the gel variable:

  • time
  • temperature
  • pH
  • concentration of polymer, salt or additive
  • ...

> Quantitative parameters (elasticity & viscosity)

  • Solid Liquid Balance: ratio between the solid-like and the liquid-like behaviour of the studied sample. Monitor properties such as: adhesion, spreadability, gel point, shape stability, physical stability, etc... 
  • Elasticity IndexElasticity strength in the studied sample. Monitor properties such as: mesh/pore size, hardness, recovery, gelation, etc... 
  • Macroscopic Viscosity Index: quantify and compare the macroscopic viscosity at zero-shear. Monitor properties such as: effect of a thickening agent, texture, flowability, long-term stability, etc... 

> Rheolact' European project

A new approach to characterize rheological phenomena taking place in dairy industry processes. Viscoelastic properties measured with Rheolaser MASTER will allow to

  • Optimize yoghurt process with special interest in raw material selection and harmonization
  • Study and reduce cheese ripening and curing times thanks to the non-contact and long term analysis

Poster

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