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Topic: Liquid Viscosity Temperature Dependence  (Read 1869 times)

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Offline chrslmx

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Liquid Viscosity Temperature Dependence
« on: December 15, 2022, 12:47:46 PM »
Hi I'm looking for some help.  I'd like to look into a viscosity effect I've noticed with various polymeric samples dissolved in organic solvents.  If I run a broad multiple temperature viscosity profile on a single sample aliquot using a scanning viscometer, say 40C, 20C, 0C, and -20C, I notice that the order of analysis has a significant impact on subsequent results.

Specifically, on a single sample injection into the scanning viscometer, running viscosities at above-ambient temperatures before running sub-ambient temperatures will decrease the dynamic viscosity results of the sub-ambient measurements (density is unchanged).

I'm speculating that this is related to macroscopic conformational changes in the polymers, and that the time it takes to run the full viscosity profile does not allow for true equilibration of these states between temperatures. 

I would like to do more research on this effect but I'm not sure what this behavior is called?  Does this fall under non-Newtonian behavior?  Or is it a different phenomenon?  Searching online for 'viscosity temperature dependence' is not helping much.  Any guidance is appreciated.


Offline Enthalpy

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Re: Liquid Viscosity Temperature Dependence
« Reply #1 on: December 15, 2022, 03:34:18 PM »
Wow, that's an interesting observation!

Personally, I'd first check with a more spherical molecule if the effect appears too. A sugar maybe, or adamantane etc, depending on the solvents used for the polymers. And also with the solvents alone if their viscosity is measurable.

Then, check at constant temperatures if the viscosity evolves over a longer time.

Conformation, yes... Or maybe the polymer isn't fully dissolved during the first measurements. If it's dissolved as pairs of parallel strands, it will deform less easily than single strands. Or the macromolecule stays packed by intramolecular van der Waals' forces for some time, and the solvent takes times and heat to unfold it.

The flow itself may stretch and orient the macromolecules.

In most technical polymers, the molecules are already stretched and oriented, purposely in fibers and films, unwantedly at injected parts.

Polyglycols serve to improve the viscosity index of lubricating oils as heat unfolds them. Similar effects should happen with POM-C and others. Does this take time? Or is there hysteresis in the temperature effect?

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