In Situ Visualization of Solvent Swelling Dynamics in Block Copolymer Films with Atomic Force Microscopy

Atomic force microscopy (AFM) imaging was used to study the in situ swelling of terraced poly(styrene-block-methyl methacrylate) (PS-b-PMMA) thin films under cyclohexane, a selective solvent for PS. These diblock copolymer terraces serve as a model system for the investigation of single-layer PS domains, which confine swelling to two dimensions. The observed network swelling is highly anisotropic with expansion occurring normal to the surface plane. Swollen terraces also become softer and are sensitive to interaction and damage from the AFM scanning probe. In this system, swelling of the terraces was observed to propagate from step edges via a sharp solvent front, separating swollen and unswollen polymer regions, indicative that dynamics are mediated by the chain relaxation rate, i.e., the kinetics follow a case II diffusion mechanism. Based on these observations, we demonstrate a technique for the local, spatially controlled doping of functional molecules into block copolymer templates, using fluorescent...