[CrimpJiggler]

In college we measured the viscosity of microcrystalline cellulose and used the result to determine its degree of polymerisation. Is the viscosity of a polymer directly proportional to its degree of polymerisation or something? In other words the bigger the polymer, the more viscous it is? Does this apply to non polymers too? For example is isopropanol more viscous than ethanol simply because it has a greater molecular weight?

[marquis]

Can't tell you about molecules in general. 

Viscosity is a common test used as a quick way to identify the relative molecular weight of polymers.  There are a number of viscosity measurements, though.  You will see viscosity measurements in size exclusion chromatography as well as more direct (but not necessarily more accurate) viscosity measurements, such as inherent viscosity, zahn cup, brookfield viscosity, and melt index.

The question is what kind of molecular weight does it correspond to?  There are so many kinds of polymer molecular weight that it gets kind of crazy.  For example, there is number average molecular weight, weight average molecular weight, etc.

A good discussion of this was done by Waters Corp.  They had a paper they put out called " A question of Molecular Weight" that discribed much of this.  Don't know if it is still on their web site, or not.

Good luck.

[TheUnfocusedOne]

The viscosity of a polymer can vary depending a lot of things. Polymer size does a good deal to do with it, but so does the degree of entanglement of the polymers, the type of polymer and the conditions you're running.

I'm guessing you used dilute solutions of the polymer dissolved in some solvent and then used one of those glass thingies to give you viscosity. If I'm not mistaken, and honestly I could be, you're looking into the intrinsic viscosity. More or less you can determine the concentration of solution, then compare it to the weight you used to figure out the average chain length. In my opinion, kinda cool but certain not as interesting as it gets.

When you're processing polymers, you have to take into account the viscoelastic properties of the polymer. A polymer exists somewhere in the spectrum between a solid and a liquid. Where it falls on the spectrum depends on the polymer itself, the temperature and the forces being applied to it at the time of measurement. The study of these relationships falls under the topic of Rheology.

Rheological properties govern the viscosity of polymer at a given temp and shear rate(look it up). There's too much to write about to keep going, I suggest going to wiki if you want more.


As far as viscosity of non polymers, it depends. Viscosity if all about the resistance of a material to flowing. Strong interactions between molecules could increase viscosity. Increasing size will also increase viscosity.