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Q & A: viscosity and packing

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Most recent answer: 05/26/2009
Q:
Are molecules in a thick liquid, like syrup or shampoo closer together than molecules in a thin liquid, like water?
- Anonymous
Nampa, Idaho, USA
A:
For these sorts of molecules at room temperature and atmospheric pressure, there's not much consistent difference in molecular packing tightness between the 'thick' (viscous) liquids and the 'thin' (less viscous) liquids. Several factors affect viscosity. Often, long-chain molecules form very viscous liquids, because the chains tangle up with each other. However, some other molecules (e.g. glycerol) which don't have long chains still form viscous liquids because the molecules happen to stick well to each other. Others which have similar size (e.g. ethanol) have low viscosity.
 It is true, however, that if you pack the molecules tighter by applying pressure the viscosity will generally go up.

Mike W.

(published on 05/26/2009)

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