Stability of polystyrene thin films containing copolymers and fe3o4 nanoparticles as additives

Abstract

This research investigates efficiency of poly(styrene-stat-chloromethylstyrene (ClMS)) (P(S-ClX)) copolymers and Fe3O4 nanoparticles as dewetting inhibitors for polystyrene (PS) thin films of thickness less than 50 nm. Chloromethylstyrene (ClMS) ratios in the P(S-ClX) copolymers are 5, 20 and 45 mol% and the copolymer concentrations are controlled to provide 0.5, 1.0, 1.5 and 2.0% of ClMS group in thin films. Concentration of Fe3O4 nanoparticles are 0.05, 0.01, 0.02 and 0.03 wt%. The atomic force microscopy and optical microscopy are utilized to follow the morphological change of the blended and filled films upon annealing above their glass transition temperature. We have found that thermal stability of the PS films is greatly improved when small amount of the copolymers is added into the system, estimates 1 mol% of ClMS group. The polar ClMS groups provide anchoring sites with polar SiOx/Si substrate while the styrene segments favorably interact with PS matrix. The effectiveness of the copolymers as dewetting inhibitors is also found to vary with molar ratio of ClMS group in the copolymers and film thickness. For polystyrene (PS) thin film filled with magnetic Fe3O4 nanoparticles, the results indicate that the addition of Fe3O4 nanoparticles suppresses dewetting dynamics of the thin film coated on Si/SiOx solid substrate. The efficiency of Fe3O4 nanoparticles depend on film thickness and Fe3O4 concentration. We expect that Fe3O4 nanoparticles provide a pinning effect followed by a decrease in hydrodynamic fluid flow process during film rupture, which in turn leads to the increase of film stability.