Why does oil stick to steel better than water?

In summary: N/m (at 25°C)Having asked this question in another, less specialised forum, I understand that it is caused by surface tension, But I still don't understand HOW it is caused by surface tension.Essentially because oil have a less surface tension than water: paraffin oil 48 mN/m, water 72 mN/m (at 25°C)http://www.kayelaby.npl.co.uk/general_physics/2_2/2_2_5.htmlI understand surface tension. I don't understand how it makes the oil stick to the steel.That's the
  • #1
jimRH9
14
0
Hullo,
I'm new here, so I'm not really sure where to post, but i supposed my question would come under physical chemistry. I am writing an essay on separation techniques in the oil industry, and I came across this machine:

http://www.oliveoilsource.com/scripts/dictionary.asp?p_do=item&p_id=45 [Broken]

I was wondering if anyone could tell me why oil sticks to steel better than water?

Having asked this question in another, less specialised forum, I understand that it is caused by surface tension, But I still don't understand HOW it is caused by surface tension.
 
Last edited by a moderator:
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  • #2
jimRH9 said:
Hullo,
I'm new here, so I'm not really sure where to post, but i supposed my question would come under physical chemistry. I am writing an essay on separation techniques in the oil industry, and I came across this machine:

http://www.oliveoilsource.com/scripts/dictionary.asp?p_do=item&p_id=45 [Broken]

I was wondering if anyone could tell me why oil sticks to steel better than water?

Having asked this question in another, less specialised forum, I understand that it is caused by surface tension, But I still don't understand HOW it is caused by surface tension.

Essentially because oil have a less surface tension than water: paraffin oil 48 mN/m, water 72 mN/m (at 25°C)
http://www.kayelaby.npl.co.uk/general_physics/2_2/2_2_5.html
 
Last edited by a moderator:
  • #3
I understand surface tension. I don't understand how it makes the oil stick to the steel.
 
  • #4
That's the reason- the interfacial energy between oil and steel is less than water and steel, so oil will displace water- the energy required to create a unit area of contact between oil and steel is less than the energy required to create a unit area of water and steel.

If you are asking for a molecular-level description of wetting, well... there isn't one yet.
 
  • #5
jimRH9 said:
I understand surface tension. I don't understand how it makes the oil stick to the steel.
Oil stick to the steel for the same reason water do: Adhesion.

http://en.wikipedia.org/wiki/Adhesion

The balancing between the two different forces adhesion and surface tension determines how much the fluid will stick to the surface.
P.S. In your first post I assumed you know what is adhesion.
 
  • #6
Andy Resnick said:
That's the reason- the interfacial energy between oil and steel is less than water and steel, so oil will displace water- the energy required to create a unit area of contact between oil and steel is less than the energy required to create a unit area of water and steel.

If you are asking for a molecular-level description of wetting, well... there isn't one yet.

OK, so My description of the machine's mechanism will probably be something along the lines of: Oil adheres better to the metal, due to it's lower surface tension. A lower surface tension means it requires less energy to adhere to the surface of the metal, compared to water. the lower energy situation is favoured, therefore only oil wets the surface of the metal.

thoughts?
 
  • #7
jimRH9 said:
OK, so My description of the machine's mechanism will probably be something along the lines of: Oil adheres better to the metal, due to it's lower surface tension. A lower surface tension means it requires less energy to adhere to the surface of the metal, compared to water. the lower energy situation is favoured, therefore only oil wets the surface of the metal.

thoughts?
Got it!
 
  • #8
I agree, with one small quibble. The term "surface tension" is taken to mean the interfacial energy between a fluid and a vacuum (or at least the liquid and vapor phase of the same liquid). The term "interfacial energy" is a better term to use, since it encompasses fluid-fluid, fluid-solid, and 'surface' interfaces.

Likewise, it's "wets" rather and "adheres".

Either way, you understand the concept.
 
  • #9
Thanks folks!
 

1. Why does oil stick to steel better than water?

Oil and water have different chemical properties that affect how they interact with steel. Oil is nonpolar, meaning it does not have a positive or negative charge, while water is polar, with a positive end and a negative end. Steel is also polar, so it is more attracted to the nonpolar oil than the polar water.

2. What is the role of surface tension in oil sticking to steel?

Surface tension is the property of a liquid that allows it to resist external forces, such as gravity. Oil has a lower surface tension than water, meaning it is more "spread out" on a surface and can cover a larger area. This allows oil to form a stronger bond with steel surfaces compared to water, which has a higher surface tension and tends to bead up on steel surfaces.

3. Does the type of oil affect how well it sticks to steel?

Yes, the type of oil can have a significant impact on its ability to stick to steel. Lighter oils, such as mineral oil, have a lower viscosity and can spread more easily on steel surfaces, resulting in a stronger bond. Heavier oils, like motor oil, have a higher viscosity and may not be able to spread as well, resulting in a weaker bond.

4. Can the temperature affect the adhesion of oil to steel?

Yes, temperature can also play a role in how well oil sticks to steel. As the temperature increases, the viscosity of the oil decreases, allowing it to spread more easily on the steel surface. This results in a stronger bond between the oil and steel. However, at extremely high temperatures, the oil can break down and lose its ability to stick to steel.

5. Are there any other factors that can influence why oil sticks to steel better than water?

Yes, there are other factors that can affect the adhesion of oil to steel. The roughness of the steel surface, the presence of impurities or contaminants, and the chemical composition of the oil can all play a role in the strength of the bond. Additionally, the length of time the oil and water are in contact with the steel surface can also affect their ability to stick.

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