Relationship between Surface Properties and Water Repellency of Fluorochemical Finishes.

Abstract

Water repellency of perfluoroalkylethyl acrylate (FA)/n-alkyl acrylate (AA) copolymers was dependent on the side chain length of the AAs. The surface properties were studied by dynamic contact angle, static contact angle and freeze-dried XPS, and the bulk ones by wide-angle X-ray diffraction and DSC. Water repellency was discussed from a standpoint of the molecular mobility of perfluoroalkyl (Rf) groups on the surface. The advancing contact angles for water were 120° and independent of the side chain length of AAs. The phenomenon was attributed to the orientation of Rf groups in air regardless of side chain length of AAs. On the contrary, the receding contact angles showed small values of about 45° for the carbon number of alkyls of AAs (n) below 8 and increased suddenly with increasing n above 12. From these results, the mechanism of water repellency was explained as follows. Low water repellency at n below 8 results from the regression of Rf groups from the water-solid interface to minimize the interface free energy. High water repellency at n above 12 shows that the motion of Rf groups was restricted due to crystallization of side chains. This mechanism was supported by other measurements.