Hydrophilic

Hydrophilic molecules interact with water. In order to interact with water, molecules must be charged or have a charged group. This is because water is a polar molecule, which means there is an uneven spread of charge over the molecule. The opposite of hydrophilic molecules are hydrophobic molecules, which do not interact with water. Phospholipids form lipid bilayers (membranes) in water because they have phosphate heads which are hydrophilic and fatty acid tails which are hydrophobic. They form the lipid bilayer so that the phosphate groups are exposed to water molecules but the fatty acid chains are not.