Stickiness / polarity measurement

[kr_bitog]

I remember in the past olefin based additive is popular due to increasing oil stickiness to engine internals. There is one time castrol promotes oil that clings to metal due to high polarity.
Just wondering if such character of oil is really important to decrease wear and oil consumption and whether there is a common measurement used for that?
Thank you

 

[dparm]

Esters do indeed have some polarity, meaning they can help an oil "stick" to metal surfaces. I've never seen any way to measure this, but perhaps one of our resident tribologists can weigh-in here.

 

[Shannow]

GrII, III, and IV aren't very polar, which means that in the past, they had some difficulties even dissolving the additives, let lone "clinging to metals"...1 and V are typically better.

Any of you old enough to remember that Mobil 1 used too use dino "additive carrier" in their M1 back in the day, to much controversy.

Doesn't matter too much when lubrication is hydrodynamic, as the parts are separated by an oil film that's way thicker then the peaks and valleys on the parts.

When the lubrication is mixed/boundary then a polar additive (like the magnatec one) may help, and there's papers out there suggesting that's the way that the industry is going.

 

[weasley]

A formulated engine oil is a large mix of molecules, some polar, some not. As mentioned above, if the base oil is highly non-polar then they do not dissolve highly polar molecules very well. Many additives have a polar moment as this is fundamental to how they work. The use of esters in PAO-based oils can help promote additive solubility. Additives also tend to be pre-diluted in mineral base oils simply to aid handling and blending.

A way of determining the 'stickiness' is the wetability of a fluid on a surface. Essentially linked to the surface tension, this gives a clue as to how the fluid spreads on a surface. The contact angle between the meniscus and the surface is a way of quantifying this. However, this is pretty academic stuff and isn't a commonly-used measure in everyday product development.

A simple polar/electrostatic interaction is only part of the story - there's a lot going on at the surface in terms of pressure, temperature and their influence on molecular alignment and interactions.