# Why is the viscosity of water and ethanol lower than that of a water-ethanol mixture?

We found in an experiment using Ostwalds method that ethanol is more viscous than water, which is already surprising as water has stronger intermolecular bonds than ethanol as @MaxW pointed out.

The mixture of both substances furthermore is significantly more viscous than both individual substances. This is interesting. We did not come up with a satisfying explanation for this behaviour.

I know that one shouldn't expect that a mixture behaves the same way or proportional to the concentration of the components, but I would appreciate an explanation of this effect on a molecular level.

• Ethanol boils at $\pu{78 ^\circ C}$ and water boils at $\pu{100 ^\circ C}$. I'd say that water has stronger intermolecular bonds. – MaxW Apr 19 '20 at 20:25
• @MaxW You're right.. I corrected this. Thank you. – TheoreticalMinimum Apr 19 '20 at 20:39

## 1 Answer

This answer just popped up when I searched for viscosity of water-ethanol mixtures, so I just copied the abstract:

Viscosities of Binary and Ternary Mixtures of Water, Alcohol, Acetone, and Hexane

https://www.tandfonline.com/doi/abs/10.1080/01932690802313006?journalCode=ldis20

"This articles studied and determined the viscosities of the binary mixtures of water–methanol, water–ethanol, water–propanol, water–acetone, acetone–ethanol, methanol–ethanol, and acetone–hexane and the ternary mixtures of water–methanol–ethanol and water–ethanol–acetone at 20°C. It is shown that the mixing of water with the alcohols and acetone resulted in a positive deviation of viscosity, which reached the maximum value at the water mole fraction x 1 ∼ 0.7 for water–methanol, x 1 ∼ 0.72 for water–ethanol, x 1 ∼ 0.74 for water–propanol, and x 1 ∼ 0.83 for water–acetone binary mixture. This viscosity deviation can be mainly attributed to the formation of micelles of alcohol or acetone molecules in water because of the hydrophobic attraction between the hydrocarbon chains. The micelle surfaces are surrounded by hydration layers, leading to the positive viscosity deviation in the liquid mixtures because the water in hydration layers has a much higher viscosity than bulk water. Also, the contrary observation was found in the binary mixtures of acetone–ethanol and acetone–hexane, having a negative viscosity deviation."