Why nanoscale droplets don't coalesce and microscale droplets do

Olive oil and water do not naturally mix. Water molecules are polar, having a net electric dipole moment due to the bend angle of about 104.5° between the two oxygen-hydrogen bonds. Olive oil is nonpolar due to its long hydrocarbon chains, which makes it hydrophobic and insoluble in water. Mixtures of the two are called emulsions, and emulsifiers exist that can stabilize them into a thicker temporary or permanent mixture. Cooks use such a technique to make vinaigrette, a salad dressing consisting primarily of oil and vinegar with emulsifiers such as mustard, honey or mayonnaise.