Uniform molecule size and viscosity modifiers

[Mad_Hatter]

Originally Posted by Rav4H2019
So are vm''s providing the padding at room temp and not the base oil ?

I'm pretty sure (plz correct me if I'm wrong on this) at room temp (40c) and below, the VM's contribute little to none of the lubes viscosity. It's only as temps increase within the engine that they become activated, uncoil and resist the base oils natural tendency to thin. At 100c and above the VM's contribution to the lubes viscosity is more significant.

 

[Rav4H2019]

Sorry I meant operating temperature. What I meant to ask:
So are vm''s providing the padding at operating temp and not the base oil ?

 

[Mad_Hatter]

Originally Posted by Rav4H2019
Sorry I meant operating temperature. What I meant to ask:
So are vm''s providing the padding at operating temp and not the base oil ?

It would serve you well to read up on VM'S. Part 2 of this 3 part "lesson" from Lubrizol addresses your question better than I can.

Lubrizol - VM's

 

[Rav4H2019]

Originally Posted by Mad_Hatter
Originally Posted by Rav4H2019
Sorry I meant operating temperature. What I meant to ask:
So are vm''s providing the padding at operating temp and not the base oil ?

It would serve you well to read up on VM'S. Part 2 of this 3 part "lesson" from Lubrizol addresses your question better than I can.

Lubrizol - VM's


Thanks. I read it. It appears at operating temperature vm''s provide the padding and not base oil ?

 

[ka9mnx]

VII's don't provide "padding". They are there to help thicken the oil at high temps so the oil can do the "padding".

 

[Mad_Hatter]

Originally Posted by Rav4H2019
Originally Posted by Mad_Hatter
Originally Posted by Rav4H2019
Sorry I meant operating temperature. What I meant to ask:
So are vm''s providing the padding at operating temp and not the base oil ?

It would serve you well to read up on VM'S. Part 2 of this 3 part "lesson" from Lubrizol addresses your question better than I can.

Lubrizol - VM's


Thanks. I read it. It appears at operating temperature vm''s provide the padding and not base oil ?

This is way out of my pay grade but I'm not sure that's a true statement, broadly speaking. I think it depends on stuff like size, shape and molecular weight. And, for example a VM polymer under certain conditions can flatten out and align itself with the flow of the base oil molecules.

I believe this phenomenon (if it's called that?) would more evenly distribute the load across [more] of the base oil molecules, which are far more resilient. This effect is referred to as temp viscosity loss or thinning. The polymer itself hasn't been cut into two pieces and returns to it's normal shape and size once the extreme forces are removed. This is one of the key differences between a high and low quality VM and is noted in the shear stability index (SSI) of the VM. Lower quality VM's will break under those forces and in doing so permanently reduces the finished lubes viscosity closer to that of the base oil. There is a finite amount of viscosity loss a lube can experience and I believe this is why lubes with a lower spread are preferred.

So anyhow... that's my best, layman's stab at that question....

 

[OilUzer]

Originally Posted by Mad_Hatter

It would serve you well to read up on VM'S. Part 2 of this 3 part "lesson" from Lubrizol addresses your question better than I can.

Lubrizol - VM's


Good link!

 

[Rav4H2019]

Originally Posted by ka9mnx
VII's don't provide "padding". They are there to help thicken the oil at high temps so the oil can do the "padding".

Then why do they shear under stress ?

 

[ka9mnx]

Because they can reach a limit just like oil.

 

[Rav4H2019]

Originally Posted by ka9mnx
Because they can reach a limit just like oil.

Let's say you had two vm''s added to base oil. One larger than base oil molecules and one smaller than base oil molecules at operating temperatures and above. Which ones would shear first. Would the vm having smaller molecules than base oil have any significant shearing ?
This is hypothetical of course.

 

[JAG]

Their molecular sizes are very large compared to oil molecules. For a given type of VM, the larger the molecule, the more tendency for them to suffer breakage (cleavage) and thus viscosity loss. On the other hand, the larger the molecular size, the more they increase viscosity, so less of them are needed. Different types of VM have a different tendency to break. Here are some basics about them. https://www.machinerylubrication.com/Read/1327/viscosity-index-improvers

 

[Rav4H2019]

Originally Posted by JAG
Their molecular sizes are very large compared to oil molecules. For a given type of VM, the larger the molecule, the more tendency for them to suffer breakage (cleavage) and thus viscosity loss. On the other hand, the larger the molecular size, the more they increase viscosity, so less of them are needed. Different types of VM have a different tendency to break. Here are some basics about them. https://www.machinerylubrication.com/Read/1327/viscosity-index-improvers


That is why I stated that it appears at operating temperature vm''s provide the padding and not base oil.

 

[ka9mnx]

I don't know how to make this more clear. Oil provides the cushion (hydrodynamic lubrication). When oil looses it film strength, anti wear (AW) and friction modifiers (FM) take over (mixed and boundary lubrication). VII's don't lubricate or cushion.

Notice in the article the author is talking about the oils ability to lubricate and protect. Not VI.

Motor Oils and Engine Lubrication
Dave Mann

Boundary lubrication exists whenever the oil film thickness becomes too small to
provide a film separation of the surfaces. The oil film has become so thin that there is no
hydrodynamic lubrication. This is where the properties of a motor oil, other than the
viscosity are very important.

An internal combustion engine imparts high shear forces on a motor oil, which is sandwiched between two
rotating or sliding forces under load and heat. The molecular structure is essentially torn
apart by these mechanical shear forces. The component of the oil that is affected most by
these shear forces is the viscosity improvers.

Another way to explain this phenomenon is as follows: If you look at the molecular
structure of a motor oil under a microscope you will see chains of molecules grouped
together and linked together. The smaller molecular particles are attached to the larger
ones. As an oil shears these smaller molecules break away and align in the chain. As
engine heat and shear forces continue and increase these molecules break away from the
base structure and in the process provide less and less resistance to wear. If this shearing
and excessive continues over an extended period of time engine damage can occur. If
shearing is only mild, then when the oil cools down the structure will revert back to its
original structure and still be capable of providing proper engine protection.

A motor oil must not be too viscous (thick) at low temperatures in order to promote easy
cold weather starting but at the same time it must not be too fluid (thin) at higher
operating temperatures in order to prevent excessive wear and prevent excessive oil
consumption. Viscosity Index Improvers (VI's) are blended in a motor oil in order to
impart specific performance characteristics to the oil under these operating extremes.

The problem that can occur in petroleum based motor oils with VI's is that under heat,
load and shear forces the molecules of the VI tend to change shape from a round shaped
molecular structure to a straightened, or aligned, molecular structure. When this occurs
the VI's are subject to degradation due to shear forces created inside the engine, which
can cause a temporary loss of the oils specified viscosity. Under shear loads the
molecules in the VI's align themselves in the direction of the shear stresses so there is
less resistance to flow. As the oil cools and the shear forces are no longer present the VI's
return to their original molecular configuration and the original viscosity is returned to
the oil. Where serious problems can occur are under extreme heat and shear loads
where the molecular structure of the VI's are permanently destroyed and will not
return to their original configuration when the oil cools and shear stresses are no
longer present.

Anti-wear additives are mainly used in order to reduce the effects of engine operating
conditions when a full hydrodynamic oil film cannot be maintained which, as discussed
previously, are known as boundary lubrication conditions of slow speed and low load.
These anti-wear additives primarily act as friction reducers that prevent metal-to-metal
contact. Zinc and phosphorus are common anti-wear additives.

 

[JAG]

Padding isn't a word I've ever heard used in tribology but I get what you mean. What matters is viscosity which varies with temperature, pressure, and shear rate (especially-so if the oil contains polymeric viscosity index improvers). The base oil's viscosity contribution to the mixture's viscosity is significant at every temperature. Likewise for the VII's viscosity contribution. The devil is in the details about how much each contributes as a function of temperature, pressure, and shear rate, VII type, and base oil characteristics. This thread helps shed some light on that: https://www.bobistheoilguy.com/foru...36188/viscosity-modifiers-ii#Post5136188

 

[Rav4H2019]

Originally Posted by ka9mnx
I don't know how to make this more clear. Oil provides the cushion (hydrodynamic lubrication). When oil looses it film strength, anti wear (AW) and friction modifiers (FM) take over (mixed and boundary lubrication). VII's don't lubricate or cushion.

Notice in the article the author is talking about the oils ability to lubricate and protect. Not VI.

Motor Oils and Engine Lubrication
Dave Mann

Boundary lubrication exists whenever the oil film thickness becomes too small to
provide a film separation of the surfaces. The oil film has become so thin that there is no
hydrodynamic lubrication. This is where the properties of a motor oil, other than the
viscosity are very important.

An internal combustion engine imparts high shear forces on a motor oil, which is sandwiched between two
rotating or sliding forces under load and heat. The molecular structure is essentially torn
apart by these mechanical shear forces. The component of the oil that is affected most by
these shear forces is the viscosity improvers.

Another way to explain this phenomenon is as follows: If you look at the molecular
structure of a motor oil under a microscope you will see chains of molecules grouped
together and linked together. The smaller molecular particles are attached to the larger
ones. As an oil shears these smaller molecules break away and align in the chain. As
engine heat and shear forces continue and increase these molecules break away from the
base structure and in the process provide less and less resistance to wear. If this shearing
and excessive continues over an extended period of time engine damage can occur. If
shearing is only mild, then when the oil cools down the structure will revert back to its
original structure and still be capable of providing proper engine protection.

A motor oil must not be too viscous (thick) at low temperatures in order to promote easy
cold weather starting but at the same time it must not be too fluid (thin) at higher
operating temperatures in order to prevent excessive wear and prevent excessive oil
consumption. Viscosity Index Improvers (VI's) are blended in a motor oil in order to
impart specific performance characteristics to the oil under these operating extremes.

The problem that can occur in petroleum based motor oils with VI's is that under heat,
load and shear forces the molecules of the VI tend to change shape from a round shaped
molecular structure to a straightened, or aligned, molecular structure. When this occurs
the VI's are subject to degradation due to shear forces created inside the engine, which
can cause a temporary loss of the oils specified viscosity. Under shear loads the
molecules in the VI's align themselves in the direction of the shear stresses so there is
less resistance to flow. As the oil cools and the shear forces are no longer present the VI's
return to their original molecular configuration and the original viscosity is returned to
the oil. Where serious problems can occur are under extreme heat and shear loads
where the molecular structure of the VI's are permanently destroyed and will not
return to their original configuration when the oil cools and shear stresses are no
longer present.

Anti-wear additives are mainly used in order to reduce the effects of engine operating
conditions when a full hydrodynamic oil film cannot be maintained which, as discussed
previously, are known as boundary lubrication conditions of slow speed and low load.
These anti-wear additives primarily act as friction reducers that prevent metal-to-metal
contact. Zinc and phosphorus are common anti-wear additives.


When a full oil film cannot be maintained the antiwear additives do their job. I get that.
But how about those scenarios where the vm molecule is going from large round molecule to a straightened one. Is that not because it is taking the initial blunt of the load. If the vm molecule was smaller than base oil molecule would it not stay a small round molecule until the oil molecules shears.

 

[ka9mnx]

"But how about those scenarios where the vm molecule is going from large round molecule to a straightened one.
Is that not because it is taking the initial blunt of the load."

Maybe I'm not understanding what you mean by load. All the load is carried by the oil. VM's are there to ensure the oil is thick enough to carry the load. VM's don't carry the load but, yes, are put under load causing them to shear (same with oil).

"If the vm molecule was smaller than base oil molecule would it not stay a small round molecule until the oil molecules shears."

Depending on it's molecular structure but generally yes. Same goes for the larger molecule. Depends on molecular structure not size.

Some synthetic oils require very little VII's, or none at all, because of their molecular structure.

 

[Rav4H2019]

Originally Posted by JAG
Padding isn't a word I've ever heard used in tribology but I get what you mean. What matters is viscosity which varies with temperature, pressure, and shear rate (especially-so if the oil contains polymeric viscosity index improvers). The base oil's viscosity contribution to the mixture's viscosity is significant at every temperature. Likewise for the VII's viscosity contribution. The devil is in the details about how much each contributes as a function of temperature, pressure, and shear rate, VII type, and base oil characteristics. This thread helps shed some light on that: https://www.bobistheoilguy.com/foru...36188/viscosity-modifiers-ii#Post5136188


Padding might not be a good word. I was thinking that at operating temperature, separation of two surfaces initially would be mostly from the largest molecules, i.e. vm molecules. Once the vm molecules reduce in size due to excessive pressure, the oil molecules would have the majority of role in separation of two surfaces. Antiwar additives separating two surfaces would be the worst case scenario. It is difficult to visualize this stuff and I thank for all the input from the various members. Anyway I am not going to fall for this "uniform molecule" touting in synthetic oil advertisements.

 

[Mad_Hatter]

Originally Posted by Rav4H2019
It is difficult to visualize this stuff and I thank for all the input from the various members. Anyway I am not going to fall for this "uniform molecule" touting in synthetic oil advertisements.

You should, because it's real and it's likely happening right now in your engine (if you're using a synthetic).

It's the engineered, uniform structure of synthetics that give it the advantages over a grp2 mineral. (higher natural VI, better oxidative and thermal stability and better performance at extreme temps)

Read this 👇 from Amsoil...
Mineral v. Synthetics - the differences

 

[Rav4H2019]

Originally Posted by Mad_Hatter
Originally Posted by Rav4H2019
It is difficult to visualize this stuff and I thank for all the input from the various members. Anyway I am not going to fall for this "uniform molecule" touting in synthetic oil advertisements.

You should, because it's real and it's likely happening right now in your engine (if you're using a synthetic).

It's the engineered, uniform structure of synthetics that give it the advantages over a grp2 mineral. (higher natural VI, better oxidative and thermal stability and better performance at extreme temps)

Read this 👇 from Amsoil...
Mineral v. Synthetics - the differences


Yes I agree to that but some synthetics have for example a blend of pao 6 and pao 8 and vm's. So this oil does not have uniformly sized molecules. I got thinking about all this is because I was thinking of taking m1 0w16 a largely pao based oil and adding a small quantity of pyb 20w50 to thicken it a tad bit for summer type temperatures. I think it will be a better viscosity modifier in warmer climates.

 

[Mad_Hatter]

Originally Posted by Rav4H2019

Yes I agree to that but some synthetics have for example a blend of pao 6 and pao 8 and vm's. So this oil does not have uniformly sized molecules. I got thinking about all this is because I was thinking of taking m1 0w16 a largely pao based oil and adding a small quantity of pyb 20w50 to thicken it a tad bit for summer type temperatures. I think it will be a better viscosity modifier in warmer climates.

Or you could just run a thicker oil in the summer months instead of playing oil formulator? Be mindful that PAO doesn't play well with [all] additives. PAO has more compatibility issues for a formulator to contemplate than say a Grp2 or 3 mineral. The mineral base stock of PYB should be fine but aside from thickening the M1, the pyb may have additives that aren't PAO friendly. (ppd's, VII's, sca's etc)

And here I thought the specd 0/16 was good year round..