hydrophilic group
Chemistry term for a functional group that has an affinity for water. Often contrasted with 疎水基 (hydrophobic group).
Surfactants have both a hydrophilic group and a hydrophobic group.
親水性 is the property of being hydrophilic, while 親水基 refers to the specific chemical group.
Compound of 親水 (hydrophilic) + 基 (chemical group). The term is a direct translation of the English 'hydrophilic group'.