Hydrophobe and Hydrophile

Hydrophobicity is the property that a molecule repels from the contact with water. You can always see leaves or grass with dews on them – if the leave or grass is hydrophobic, the dew would tend to look like a perfect sphere. And the dew rolls down easily when you gently shake the leave. A hydrophile, on the contrary, likes interacting with water molecules. A water drop on a hydrophilic surface has the contact angle smaller than 90 degrees.

Then why do I study about if my materials are hydrophobic or hydrophilic? What does it have to do with graphene/polyamide nanocomposites?

Firstly, to create nanocomposites, I need our two components like each other. Graphene, being hydrophobic, is hard to go along with the process of incorporation. (It’s just carbon. What can I expect?) So I turn to graphene oxide, which is more hydrophilic but at the same time carries a lot of properties of graphene. Starting from graphene oxide, I will gradually see differentiated carbon/oxygen ratios influence the interface of nanocomposites.

Besides, I have introduced the Atomic Force Microscopy (AFM) in my first blog. AFM is able to ‘draw’ the topography of a sample within the nanoscopic scale, which is why it is a great instrument to identify graphene oxide. As you can imagine, I need a super flat substrate for graphene oxide to lie on. And the substrate had better be hydrophilic because when I spin-coating it with graphene oxide, which is dispersed in water, the drop of sample must stay on the substrate instead of being whipped off at the very beginning of the spinning process. If the substrate likes water enough, the drop is able to stay at the center of the substrate. And as it is being spun, the drop carrying the graphene oxide will expand. The surface of the drop becoming bigger allows water to evaporate and leave graphene oxide on the substrate.

For some substrates, the property of being hydrophobic could be changed so that I can take the advantage of it being very flat!