Suspension viscometer: measuring the viscosity of complex liquids

What is a suspension?

A suspension is a heterogeneous mixture in which solid particles—either insoluble or nearly insoluble—are dispersed in a liquid phase. These systems are thermodynamically unstable and composed of two distinct phases:

• A continuous, dispersing liquid phase.
• A discontinuous, dispersed solid phase.

Suspensions may settle if stirring or flow is insufficient, which can cause issues in piping systems, such as:

• Uneven distribution of solid particles.
• Accumulation of solid phases at the bottom of the pipelines.
• Flow blockages.

What factors influence the viscosity of suspensions?

Adding suspended or dissolved substances alters the viscosity of the mixture. Several parameters affect the viscosity of suspensions, including:

• The concentration of solid particles.
• The size and shape of the particles.
• Interactions between the liquid phase and the suspended particles.

Flow curves that describe how viscosity changes with shear rate show that suspensions—especially at high concentrations—typically exhibit non-Newtonian behavior, most often shear-thinning (pseudoplastic). Although less common, some suspensions display shear-thickening behavior. Others may be thixotropic, meaning their apparent viscosity decreases over time under shear.

Application example: Zinc oxide (ZnO) mineral suspension

Zinc oxide is produced in various ways, such as from zinc hydroxides generated during sodium dithionite production. The oxide is then cooled and purified to obtain the purest possible form.

During purification, ZnO concentration plays a crucial role in ensuring that the final product meets customer specifications. Throughout production, viscosity offers an indirect measurement of concentration.

This nearly water-insoluble oxide typically appears as a powder or as white or yellow microbeads. It is infusible and exhibits complex rheological behavior.
Zinc oxide is used in various industries such as food and petrochemicals. It plays a key role in rubber manufacturing by accelerating vulcanization kinetics, and is also an essential component in powder-based pharmaceutical formulations.

Depending on particle size and formulation, these suspensions may exhibit different rheological behaviors.
In sunscreens, for instance, zinc oxide is dispersed in either an oil or water phase. The viscosity of the final product depends on the ZnO concentration and interactions between the particles. High concentrations may result in thixotropic behavior, allowing easier application while ensuring strong adherence to the skin.

Sofraser’s MIVI viscometer: the ideal solution for suspensions

The MIVI, Sofraser’s best-selling vibrating type viscometer, offers a reliable and reproducible solution for measuring the viscosity of suspensions. Its vibrating principle provides multiple advantages:

• It gently repels particles from the micro-layer in contact with the active part of the sensor, making it abrasion-resistant.
• It delivers real-time, 24/7 continuous measurements.
• It is compatible with the most demanding industrial environments.
• It offers accurate viscosity measurement, as well as correlated values like concentration and phase detection.

Integrating it into industrial processes improves final product quality, reduces waste, and ensures efficient production.

Common suspension applications:

• Rice pudding
• Drilling mud
• Inks
• Paints
• Cream cheese
• Cement slurry
• Slurries
• Ceramics, pastes, and glazes
• Yeast suspensions