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Viscosity and rheology modifiers

Viscosity and rheology modifiers are substances that alter the viscosity (or "thickness") of a liquid. Viscosity modifiers alter a fluid’s resistance to flow. Rheology modifiers can do the same thing, but may include additional abilities, like change the viscosity of a fluid depending on the forces that are being applied.

All of our viscosity and rheology modifiers alter the properties of liquids but the reason why a product is chosen will depend on the specific application conditions. For some applications, thickening a formulation will help with the manufacture of a product (improve the production process), where for other applications, a modifier will help to create the final product.

We provide:

  • Rheology modifiers for catalysts washcoat manufacturing
  • Viscosity modifiers for lubricants
Close up of engine components lubricated using viscous lubricants and greases

Rheology modifiers for catalysts

We offer a range of products that help to optimise the production process of catalysts and catalytic converters. If you wish to view our range of dispersants for catalyst washcoats, please click here.

To complement our dispersants, we also have a range of rheology modifiers that allow you to have control, whether you are looking for thickening, shear thinning, pseudoplastic or thixotropic behaviour.  These can be used over a wide pH range and some provide instant thickening to save you time.

Our high performance rheology modifiers are based on a range of technologies and are able to give formulators the desired rheological characteristics to both aqueous and non-aqueous formulations.

Viscosity and rheology modifiers for lubricants

Lubricant viscosity modifiers are highly viscous products that increase the viscosity (the thickness) of an oil or a grease base oil. The base oil is usually treated before the final formulation is created. Viscosity modifiers do not alter the temperature viscosity curve, but instead increase the viscosity at the same rate across all operating temperatures. (products used to increase the viscosity at elevated temperatures are called viscosity index improvers).

Why are lubricant thickeners used?

In many applications, the lubricant’s base oil is not viscous enough and must be thickened. Film strength plays a key role in the proper lubrication and protection in applications such as industrial gear oils, where extremely high pressures are exerted on the moving parts. Film strength is directly related to its viscosity and viscosity reduces as temperature increases and at higher shear rates, so a good viscosity modifier will perform at elevated temperatures and at high shear.

What viscosity modifiers do we offer?

We manufacture complex ester viscosity modifiers with a viscosity as high as 40,000 cST at 40°C. suitable for treating Group I, II and III base oils.

Brochure: Rheology and dispersion control for catalyst manufacturing

Complex road network with one car travelling at speed using viscosity modifiers
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Marketing sheet: Recommendations for Complex ester thickeners for lubricants

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How do Priolube™ complex esters compare with polyalphaolefins (PAOs)?

The table above shows a number of high viscosity complex esters which can be used in the formulation of transmission fluids. High viscosity esters are typically used as thickeners, but they have the added benefit of acting as film formers/anti-wear additives under low speed/high load conditions. PAO 100 and PAO 1000 are also shown in the chart for comparative purposes as these are traditionally used as thickening agents. 

High viscosity esters have a number of benefits compared to PAOs:

  • They are renewable
  • Priolube 1847 and Priolube 3986 are both featured on the LuSC list, making them suitable for use when formulating EU Ecolabel compliant lubricants
  • They have excellent shear stability properties
  • They are more cost effective than PAOs, especially PAO 1000.
  • Priolube 3986 especially has excellent film forming characteristics (see below).

What are the film forming properties of high viscosity esters?

By cleverly controlling polarity, a viscous surface film can be developed

Hydrodynamic – The more polar thick complex ester sticks to the surface. Bulk viscosity can still be low giving good efficiency


Elastohydrodynamic – At low speed, the bulk lubricant is squeezed out of the contacts. The thicker, more polar complex ester remains. This boosts film thickness, reducing wear and improving fatigue life

High viscosity complex esters have the ability to migrate to metal surfaces and form viscous films which prevent metal - metal contacts under high loads and slow speeds. Under low loads and high-speed conditions, even though the complex ester has migrated to the metal surfaces the lubricant film thickness, the frictional characteristics and wear properties of the lubricant are dictated by the viscosity of the bulk fluid.

However, at low speeds and/or high loads the metal surfaces are forced closer together. It is under these conditions that the benefits of the high viscosity ester can be seen. Having migrated to the metal surface the ester acts to prevent metal – metal contact through having formed a viscous protective layer. This helps to reduce wear and improve fatigue life of the system under load.

The film forming properties of complex esters can be demonstrated using an EHD Interferometer test rig.

How do we test our complex ester viscosity modifiers?

We use interferometry to determine the thickness of an oil film. Coherent light (single wavelength in-phase) is focussed through a silica coated glass disc onto the surface of a ball, which is then reflected into a spectrometer and through a camera into a computer. The shift in phase between light reflected off the silica layer and ball is used to determine the distance between the two, and consequently the film thickness can be calculated.

What are the film forming characteristics of Priolube complex esters?

The chart below demonstrates the film forming characteristics of Priolube 3986 compared to PAO 100. PAO 2 has been used a base fluid to which is added 5 % Priolube 3986 to one test fluid and 5% PAO 100 to another test fluid.

At high speeds, the high viscosity components have little effect on the film properties of the lubricant - this is determined solely by the viscosity of the bulk lubricant. However, as the relative speed of the ball and disc is decreased, the bulk lubricant is squeezed out of the contact zone and the film thickness decreases. At lower speeds, the film thickness is dependent upon the film forming properties of either the complex ester or the PAO 100.

In the case of the PAO2 / Priolube 3986 formulation, the complex ester film remains intact on the metal surfaces. This results in a significant boost in film thickness compared to the PAO2 / PAO 100 formulation and by inference, can contribute to minimising wear. Note that it is generally necessary to add an equivalent amount of Priolube 3970 to solubilise the P3986 into the formulation.

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