Water-attracting vs water-avoiding
Key for solubility and membranes
Hydrophilic substances interact favorably with water, usually because they are polar or charged. Hydrophobic substances interact poorly with water, usually because they are nonpolar. This contrast explains why salts and sugars dissolve in water, why oils separate from water, and why phospholipids self-assemble into membranes with hydrophilic heads and hydrophobic tails.