Rim instability in polymethylmethacrylate films on self-assembled monolayers with the hydrophilicity

The solvent-induced dewetting of polymethylmethacrylate (PMMA) films prepared on self-assembled monolayers (SAMs) supported by Si substrates was investigated with the hydrophilicity of the SAMs. Dewetting of the PMMA film was characterized as a function of the surface energy of the SAMs. At lower surface energies, the rim instability was found to be of type B. Type B instability created undulations in the rims of holes. As the holes merged, fingers and then droplets formed. At higher surface energies, the rim instability of the PMMA films was of type A. Type A instability did not form fingers. The formation of PMMA droplets was dominated by the total spreading coefficient (S) of the PMMA film on the SAMs, which can be expressed as the sum of the dispersion (S-d) and the polar components (S-p) of the spreading coefficient. Sd of the PMMA films decreased, whereas S-p increased as ultraviolet (UV) irradiation for periods of time between 0 s and 100 s, respectively. This result suggests that S-d destabilized but S-p stabilized the PMMA films. (C) 2011 Elsevier Ltd. All rights reserved.