Density of Oils

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Sep 19, 2008
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I have not seen this discussed on here but if it has , I apologize for the repeat. Looking at the densities of various polyethylenes, one can arrive at some knowledge of the structure of those polymers, with significant branching causing, generally, a reduction in density. I am curious if anyone has tried to correlate overall density of a lubricating oil to the percentage of PAO, Type III, etc. Some of the syn oils have a very low density, it seems. Any thoughts on this??
 

JHZR2

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all organics have densities of roughly 0.66 to 0.9 g/cc. Some polymers go up to 1-1.2. Obviously there are other that do not vary on this trend, but there are, IMO, too many variables to do this reasonably well. In the end all, the add pack is as important as basestock for the most part, and the "value proposition" of having loads of PAO in the oil is not the best evaluation. In reality, the best oil is that which makes the best UOA reports for your engine and driving profile. You can see some trends in the VOA sections, so give that some consideration...
 

Boomer

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Thanks, Pablo. I had seen some of those M-1 numbers and that was what drove the question. I know PE sdensities are made more complicated by the percent crystallinity of the polymer. Looking at whether PAOs are different in density from Type III oils, for example, is not to indicate "goodness" of the oil but just composition. My curiousity was piqued just seeing some of the numbers. Along a similar line, I wonder if in a hydrodynamic wedge of lubricant if different fluids respond differently. Will one show a small density change under about 6000 psi while another may show almost noe? This is caused by molecular reorganization under pressure, similar to ice melting under the pressure of a skate to form a water film. I know this is speculation on my part but it is the kind of thing that kind of gets me thinking about how different fluids might differ in lubricity.
 
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