Effect of the Hydrophilicity of the Sublayer on the Dewetting of Thin Polymer Films

Abstract

The thin polymer film plays an important role in industrial and technological applications, including in bio-membranes, patterned technology, micro-devices, and lithography. The dewetting of the polymer film has been studied extensively over the past several decades. In this thesis, the dewetting of polymer films prepared on the self-assembled monolayers (SAMs) supported by Si substrates was investigated by using the various condition of dewetting under solvent-induced and thermal annealing.In Chapter I, a motivation and theoretical backgrounds of this study is briefly introduced for the dewetting of polymer films on the SAMs.In Chapter II, rim instability in polymethylmethacrylate (PMMA) films on the SAMs with the hydrophilicity was investigated by using the ultraviolet (UV) irradiation onto the surface of octadecyltrichlorosilane (ODTS). 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 (Sd) and the polar components (Sp) of the spreading coefficient. Sd of the PMMA films decreased, whereas Sp increased as UV irradiation for periods of time between 0 s and 100 s, respectively. This result suggests that Sd destabilized but Sp stabilized the PMMA films.In Chapter III, the slip transition of polymer films on a hydrophilic homogeneous self-assembled monolayers was investigated as a function of the hydrophilicity of the SAMs surfaces. To this end, the dewetting kinetics of thermally annealed PMMA films was measured as a function of the SAMs surface energy for SAMs prepared using ODTS. At lower surface energies, the dewetting behavior of PMMA films desplayed two or three stages. Radius of holes (R), R  t0.72-0.78, where t is the dewetting time, the width (W) of the rim simultaneously increased, whereas slip did not found with t increased, R  t0.34-0.39. The slip of PMMA films was dominated by the viscous friction between the PMMA films and the SAMs. At a higher surface energy, the PMMA films did not display slip. R grew as t0.45, not W of the rim increases, but R of holes increase only. The spreading coefficient (S) of the PMMA films approached zero for UV exposure times between 0 s and 180 s. The affinity of the PMMA chains toward the SAMs increased, and the stability of the PMMA films increased. We concluded that UV irradiation of the ODTS layer provides a method for stabilizing the PMMA films by improving the wettability of the SAMs.