Hydrophilicity and HydrophobicityMembranes in an aqueous environment have an attractive or repulsive response to water. The material composition of the membrane and its corresponding surface chemistry determine the interaction with water, thus affecting its wettability.The wettability of a material is a surface property characteristic which yields a unique value for each material. The surface tension value of a material can be utilized to determine wettability of a material by specific liquids. Through the measurement of the contact angle between a solid surface and a droplet of liquid on the surface, the surface tension for the solid material can be calculated.The surface tension is an internal force, due to an unbalance in molecular forces that occurs when two different materials (e.g. a liquid droplet on a solid surface) are brought into contact with each other forming an interface or boundary. The force is due to the tendency for all materials to reduce their surface area in response to the unbalance in molecular forces that occurs at their points of contact. Surface tension values will vary for different systems of liquids and solids. Examples of surface tensions of various polymeric materials are shown in the Table.