Oil Polarity

[Tempest]

After reading the thread on long standing engines and start up, it got me thinking about polarity. Bruce said:

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IMHO PAO and GPIII oils are lousy at "wetting" a mineral or high ester oil like RL will IMHO "wet" and thus stay on longer than a PAO/GPIII.

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So what makes the difference, or an oil polar? The Chevron Base Oil site for GrpII shows about double the quantity for Naphthenics vs. GrpIII. The GprIII's all show ~0% for Aromatics, vs. ~1% for GrpII. Are these the elements that affect polarity?

I assume the higher Nap/Aromatic % is what gives the GrpII better solvency but poorer volatility and oxidation? (On a side note) And that Grp I would have even higher amounts of both and be even more polar?

There is a Macromedia demo of an ester product that can be seen Here. And a Power Point demo Here (7.5 MB). These are for marketing, but they do seem to have some useful info.

It shows esters as "sticks" that polar bond to the metal. Would these "sticks" help less polar oil to cling to the metal?...or would it actually repel it? I welcome those in the know to comment.

 

[Vilan]

Chemistry lesson ahead! I'm no teacher but I do have a degree in chem. Let's see what I can remember.

For a molecular to be polar, there must be some part of it that is electron-rich/poor. Most oil compounds are just made of carbon and hydrogen, which share electrons pretty equally. But esters do have an electron-rich oxygen site in them, like that video shows.

If the polar part is attracted to metal, and I'm not sure that it's really as strong as that video shows but let's assume it is, the non-polar "stick" part of it will be facing out. Non-polar stuff prefers to stay together with other non-polar stuff (aka oil and water don't mix), and most oil compounds are non-polar, so other oil would stay in those "sticks" and thus be repelled from the surface.

Kind of the same idea as how soap works... water is polar so it can't dissolve dirt much. But with soap, the non-polar bit of the soap sticks itself in the dirt, the polar part sticks into the water, and the dirt gets carried off.

I hope you are now confused on a higher plane than before.

http://en.wikipedia.org/wiki/Chemical_polarity

http://en.wikipedia.org/wiki/Ester

 

[Tempest]

Thanks for the info Vilan...good stuff there. Especially for esters. But it still doesn't explain why a Grp I or II would be more polar than a Grp III/IV since these are all the non/low polar hydrocarbons you mentioned.

Any other ideas?

 

[bruce381]

Polar as far as I use the term in lubes is when a oil or additive will enhance the "film strenght" of a lube.

Esters and fats aswell as some other additives will improve metal "wetting" and sticking aswell as raise the film strenght of the oil and reduce friction.

Forgot exactly how something about the ester/fat haveing a oil soluble end or head which sticks out into the oil the other end or head has an attraction to metal and will stick the that.

Baisc stuff I forgot but that is idea I think.
bruce
Teflon will not wet out on metal just floats around will not burnish into metal as a moly will.
teflon is just chunks of plastic nad has limited lube value.

 

[boxcartommie22]

are there ester additives?

 

[boxcartommie22]

lubegard is one

 

[Blue99]

I think the concepts of soluability & the polar characteristics of an ester are getting mixed up here.

Naphthenic base oils have higher naphthenic molecular content than Grp II paraffinic stocks and are rated good for soluability performance.

But the naphthene structure, in itself, is not polar.

A characteristic of esters is the polar nature. Esters will “creep or migrate” across a metallic surface and this characteristic makes it a good component for penetrating oils.

I know I’m repeating myself, but the best example I have of ester “creep” is the opened, 1/2 bottle of Mobil MX2T 2 cycle oil I have on my workbench shelf. The outside of the bottle & the shelf surface are “slimey” due to a film of esters creeping out thru the cap & down the exterior surface of the bottle.

 

[Tempest]

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I think the concepts of soluability & the polar characteristics of an ester are getting mixed up here.

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The only reason I brought up Naphthenics and Aromatics was that I was trying to look into the differences between Grp I/II and Grp III/IV. Bruce said the former tend to cling better than the latter, just trying to find out why.

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the best example I have of ester “creep” is the opened, 1/2 bottle of Mobil MX2T 2 cycle oil I have on my workbench shelf.

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Is the bottle metal? Or do esters exhibit this tendency with all materials?

 

[Tempest]

Ok, in a PM from Bruce (thanks!), he stated that in his experiance oils with a higher aniline point (less aromatics/naphthelens) tend to wet/cling worse than those with lower aniline points (more aromatic/naphthelens). From Wiki :

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Solvents and solutes can be broadly classified into polar (hydrophilic) and non-polar (lipophilic). The polarity can be measured as the dielectric constant or the dipole moment of a compound. The polarity of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible. As a rule of thumb, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best: "like dissolves like". Strongly polar compounds like inorganic salts (e.g. table salt) or sugars (e.g. sucrose) dissolve only in very polar solvents like water, while strongly non-polar compounds like oils or waxes dissolve only in very non-polar organic solvents like hexane. Similarly, water and hexane (or vinegar and salad oil) are not miscible with each other and will quickly separate into two layers even after being shaken well.

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So one could conjecture that any polar aromatics are helping to wet the metal...