Self-Organized Wrinkling in Thin Polymer Films under Solvent–Nonsolvent Solutions: Patterning Strategy for Microfluidic Applications

Self-organized wrinkling instabilities in thin polymer films have instigated a field of versatile surface patterning and have spurred several research efforts in developing micro- and nanopatterned templates for a wide range of applications. Here, we report for the first time a distinct class of wrinkles in a thin polymer (polystyrene, PS) film coated on a substrate under a mixture of organic solvent and aqueous nonsolvent. The solvent (dimethyl formamide, DMF) softens and swells the polymer and paves the way for wetting of the hydrophilic substrate (≥46 mJ/m2) by the solvent–nonsolvent (S-NS) mixture, leading to wrinkle formation. It is investigated that selective delamination-induced wrinkling is a generic phenomenon and takes place in various polymers as well as different combinations of solvent–nonsolvent mixtures. The surface energy of the substrate and the composition of the solvent–nonsolvent mixture play a critical role as wrinkling is not observed on substrates with lower surface energy (