surfactancy/dispercancy vs. shear forces

Not open for further replies.


Staff member
Dec 14, 2002
New Jersey
Molakule, etc.:

I have a question regarding the design of the dispersant packages used in motor oils.

It seems to me that optimally, we would design an oil that would allow particles suspended in the oil to loosely aggregate/agglomerate, due to weak van der waals or DLVO type forces.
Under a slight amount of shear, such as occurs in an engine (many instances in an engine that are extremely smilar to any commonplace rheometer), these weakly aggregated particles would break apart, and cleanly flow through any narrow passages. However, in a large fluid body, such as the oil sump, the particles would be able to aggregate and thus plug themselves in the oil filter.

I have done numerous studies of interparticle interactions in situations such as stirred media mills, etc. Varying the surface chemistry to keep the particles permanently separated seems to me to almost be kind of dumb in an engine. It would be preferable to me to get the particles weakly aggregated, and then lodged in a full-flow/bypass filter system, where they won't get out.

Having dispersed fine particles permanently in the system seems to have the potential of being a problem. Of course, engine life and UOA show otherwise, but has thought ever been put into removing the particles rather than dispersing them? Seems oils could last a lot longer this way in situations like diesels, where soot is the limiting factor.

Now I kinda know what a "surfactant" is ...and how it acts in aggitated solutions.....


Would you mind "dumbing" that high powered rhetoric down a little for the "technical writings" challenged?? (visions of grabbing the Honeywell engineer who wrote the PLC manual by the tie and forcing him to meet a hard place while asking him to be more sensitive
Gary Allen,

Loved the picture. My physics class would love it!


Please clarify what particles you are discussing; solubles, insolubles?

The micelles in an oil soluble soap (dispersant) essentially surround or trap hydrocarbon sludge particles, while the detergents hold insoluble materials in suspension. Not sure what is so dumb about that.

You have combustion products (often polymerized) by hyperoxides that need to swept away so they do not agglomerate into larger sludge particles. In a mill, you do not have combustion byproducts, so were talking apples and oranges.

Your interparticle studies involved what, polar attractions, brownian motion, ?

[ March 06, 2004, 01:17 PM: Message edited by: MolaKule ]
My basis was more insoluble particles, like soot that gets loaded up in the oil.

I understand the fact that there is combustion here. But my thinking was essentially, why not allow the particles to aggregate, so they can be picked up in a good filtration system, rather than loading the oil up with these small particulates (soot, for example), and then draining it when loading was maxed out.

My studies mainly involved harnessing the DLVO forces to attempt to study why after some point (500nanometers, typically), milled particulate solutions tended to get into a shear-thickening regime and aproach nearly an asymptote when we plot power input vs particle size. It hasd taken foot and is an IFPRI project now.

I dont know if its that relevant, probably because I don't quite understand what makes up oil sludge. But soot is the big factor to me, as I drive diesel cars. And those small particles are typically what decides the OCI.

eseentially what I was trying to ask was:

-there are particulates such as soot in the oil. These particles tend to get dispersed by the oil's additive package, so they dont make big, abrasive aprticles.

Sometimes, when large particles are aggregates of smaller ones, a shearing force will break them back down into their smaller component particles. My thinking was, if we allowed the particles to aggregate into bigger ones, we can catch them in a good filtration system, and they dont have to be loaded int he oil. If they do wget inbetween the bearings, etc., they could shear down into very small particles that would effectively flow right through in the film of oil.

But maybe Im thinking completely wrong?!?


You're on the right track, except I think you're missing a minor point.

Here is the problem. The oxidation of the oil by hyperoxides, along with sheared VII and oil molecules (and other hydrocarbons), create sludge particles. These sludge particles are further polymerized by heat and moisture to form these larger sludge globules. If these globules weren't broken up by the DD package and solved, the size and viscosity of these globules would increase. Soot particles solved by the DD package are both hard and soft, varying in size, with some as soft as pencil lead dust, and some almost as hard and abrasive as diamond. All of this will happen before before we get the opportunity to aggregate the smaller particles into larger ones.

In other words, it is much better to solve the particle(s) while they are small and put them into solution. Keeping the particles small and unaggregated before they can form into larger particles that get between bearing surfaces and cause wear, is the key. In addition, some of the additives in the oil and the base oil itself will soften carbon particles. Once such aftermarket product that does this well is LC.

If you're interested in what particle sizes cause the most wear, PM me and I can send you technical paper references.

Good luck on your study. Sounds interesting.

Shearing these large abrasive partiles into smaller ones, for example, by letting the rings shear them, would accelerate wear.
Since you've tread into the realm of surfactants........ is there any use of chelates in motor oil? Some results suggest that AutoRx, in its ability to dislodge and harmlessly transport particles, in fact "encapsulates" them so that they can be filtered out ...yet pass between bearing surfaces without any abrasive effects.

In industrial water treatment I've used both anionic and cationic polymers for particle precipitation/coagulation (flockulation) and have used chelates to snag copper out of the waste stream.
Not open for further replies.