Spreading of perfluoropolyalkylether films on amorphous carbon surfaces

Spreading of perfluoropolyalkylether thin films on amorphous carbon surface s has been studied by scanning microellipsometry. Two types of perfluoropol yalkylethers with the same main-chain structure and various molecular weigh ts (between 1000 and 6000 g/mol) were used: Zdol, with OH functional end gr oups, and Z, with nonfunctional CF3 groups. For Zdol, the thickness of the molecular layers in the spreading profile increase as Mn-n(0.6), where M-n is the mean molecular weight,with the second layer being nearly twice as th ick as the first layer. This layered structure was not observed for Z in th e molecular weight range under study. As expected, the thickness-dependent diffusion coefficient D(h) was found to decrease with increased molecular w eight. Possible molecular conformations near the solid surface are discusse d. The spreading of binary blends of Zdol-Zdol, Z-Z, and Zdol-Z were also s tudied. The results show that the spreading of the binary blend of the same kind of polymer with different molecular weight behaved like that of a lub ricant with an intermediate molecular weight. The diffusion coefficient of a blend was found to obey the additivity of viscosity. For Zdol-Z blends, h owever, the faster moving Z molecules migrate through the network of the sl ower moving Zdol molecules, and form a monolayer ahead of Zdol. (C) 1999 Am erican Institute of Physics. [S0021-9606(99)70506-4].