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Hydrogen in it's liquid form has zero viscosity but water is the smallest molecule, and so despite its ability to readily hydrogen bond, it is the least viscous. The main constituent of rubbing alcohol is isopropanol, which retains and ability to hydrogen bond, and is also larger than water. Vegetable oil is made up of lipids, which have long, hydrocarbon chains, and so is more viscous due to this effect. Ethylene glycol, while not as long a molecule as the lipids in vegetable oil, is polar, and has a greater ability to hydrogen bond, due to having two hydroxyl groups. This makes it the most viscous of the liquids tested.
The viscosity of a liquid always decreases as temperature increases. As the molecules acquire more energy, they can escape from their mutual traction more readily. Long-chain molecules can also wriggle around more freely at a higher temperature and hence disentangle more quickly.

11 years ago. Rating: 8
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