Improvement of ultrathin polystyrene film stability by addition of poly(styrene-stat-chloromethylstyrene) copolymer: An atomic force microscopy study

A method to improve the stability of ultrathin polystyrene (PS) films on SiO_x/Si substrate is introduced. In this method, interfacial interactions between PS film and substrate are enhanced by addition of poly(styrene-stat-chloromethylstyrene(ClMS)) copolymer containing 5 mol% of ClMS group. The resulting slight structural modification of the copolymer does not cause phase separation in the polymer blend. On the other hand, the existence of polar ClMS groups provides anchoring sites on the polar SiO_x surface via dipolar interactions. In this study, ratios of the copolymers are varied from 0 to 40 wt.% in the thin films resulting in a systematic increase of the interfacial interactions. The dewetting behaviors of all films subjected to the same annealing conditions are explored via atomic force microscopy. The analyses of root mean square roughness and dewetting area as a function of annealing time and copolymer ratio provide information about the film stability. Our results indicate that blending small quantity of the copolymer with PS significantly increases the stability of ultrathin films.