what makes something hydrophobic?
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Water’s main property is that the side with the Hydrogens is slightly positively charged, while the side that is mostly Oxygen is slightly negatively charged. This let’s water stick to itself, the way a magnet sticks to other magnets.
Hydrophobic materials are just ones that *don’t* have any preferred charge at any side. This is usually long chain molecules, because short molecules are very often at least a little charged. You could imagine it as a piece of lead in a sea of magnets.
It’s not that water is specifically repelled from them, just that water attracts more to everything else, including other water.
Adding to this, some hydrophobic surface have structure that reduces the surface contact with the water droplet. A bit like a Fakir bed of nail for instance (but microscopic), because of the surface tension when water droplet doesn’t go between the nails. So it just glides away because it’s actually barely touching anything.
However, if I’m not mistaken, the most important point is the “non polar surface” as described before.
No matter what you do, if your surface actually attracts water it will simply stick to it.
First you kinda have to know what polar/non-polar is. Water is polar, meaning that there is an imbalance of charge. Electrons gather in certain areas of molecules and this is the place where the negative charge is. For water this is at the oxygen. The other side of water is positive by default.
The opposite is a non-polar molcule which has equally spread out electrons/charge. So there is no negative or positive side.
Anyways, polar molecules and non-polar molecules don’t like each other. They don’t mix. well. But polar and polar molecules do, and so do non-polar and non-polar molecules.
So since water is polar, its not going to mix well with non-polar molecules, like oils and gasoline. So what makes something hydrophobic is that it is non-polar.
Its polarity.
Liquids can be polar or non-polar. Water is a polar liquid because of the difference in “charge” between hydrogen and oxygen. Hydrophobic liquids are non-polar and include oils/hydrocarbons (long chains of carbons singe-bonded to hydrogen)
Plastics/ polymers are hydrophobic because they are largely made up of long hydrocarbon chains which is why rain coats are made of nylon and such.
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