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/m(2)) 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 (<46 mJ/m(2)). An isotropically distributed yet disordered self-organized wrinkle network of hollow buried channels is formed, and it is illustrated that these can be exploited to generate a mesh of microwires and harnessed to form highly directional patterns using electron beam lithography, which can turn the new leaf for nano- and microfluidic device fabrication platforms.

Automated summary

Self-organized wrinkling instabilities in thin polymer films have led to the development of versatile surface patterning techniques, with the potential to create highly directional patterns using electron beam lithography for nano- and microfluidic device fabrication. The composition of the solvent-nonsolvent mixture and the surface energy of the substrate play crucial roles in the formation of wrinkles, which can be exploited to generate a mesh of microwires.