Mikrorheology MS-DWS

Microrheology enables the measurement of the evolution of viscosity and elasticity, in bulk samples, without any mechanical stress. The measurement is performed at rest, allowing to monitor sample evolution, such as gelation, rheology ageing, or samples stability. The measurement is performed in a closed glass cell, preventing any evaporation or drying, and making it safe to operate at all time.

Instrument

Measurement principle

The microrheology analysers of the RHEOLASER-range use MS- DWS (Multi-Speckle Diffusing Wave Spectroscopy) principle of measurement. It corresponds to Dynamic Light Scattering extended to concentrated dispersions. It measures the particles Brownian motion, which depends on the viscoelastic structure of the sample. This technique consists in sending a coherent laser beam into the sample, leading to interfering waves which create a speckle pattern captured with a video camera detector. The variations of this speckle image are directly linked to the particles Brownian motion, their speed and the distance they explore.

How it works – MS-DWS (Multi-Speckle Diffusing Wave Spectroscopy)

Benefits and key features

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 to measure MSD curves as a function of time or temperature, allowing to monitor stability, or gelling process…

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

This enables to monitor any kind of gelling process, no matter the gel variable:

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

Solid-Liquid-Balance (SLB):

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 Index:

Elasticity 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…

Main Advantages

• Measurement at rest, non-invasive and non-destructive
• One-click experiment setup and results
• Kinetic or aging analysis on the very same sample
• Hazardous samples can be analysed in a closed glass cell

References and norms

/1/ Partikelwelt 16, S. 3-6 “Mikrorheologische Untersuchungen von Gelierungsprozessen nach dem Time-Cure-Superposition-Verfahren”