(79i) Periodic Pattern Formation of Thin Polymer Films Guided by Electrostatic Charges On the Substrate
Self-organization of thin polymer films into periodic and functional patterns is important both scientifically and technologically. Electric field has been exploited as an efficient and powerful means to induce the destabilization and self-organization of soft materials. Previous attention, however, mainly focused on externally applied electric fields. In this presentation, we show that internal electric field induced by static charges on the substrate can be strong enough to guide the self-destabilization of thin polymer films into periodic patterns too. We first introduced patterns of electrostatic charges with micron-resolution on dielectric substrate, e.g., silicon oxide. A thin polymer film was then spin-coated onto the topographically flat substrate. Upon thermal annealing, thin polymer film destabilized due to a lateral gradient of electrostatic stress and flew away from the electro-neutral regime to charged area, resembling the patterns of charges on the substrate. Our theoretical and numerical modeling based on the electrohydrodynamic instability showed excellent agreement with experimental observations both qualitatively and quantitatively. We also demonstrated that the interplay between charge-driven instability with spinodal dewetting and Rayleigh instabilities can generate fine and hierarchical polymeric patterns that are completely different from the charge patterns pre-introduced on the substrate. Our study provides the direct evidence that internal electric field is strong enough to destabilize thin polymeric films and generate periodic patterns. This study also demonstrates new strategies for bottom-up fabrication of structured functional materials.