Solvent-Induced Instabilities in Electrospun Polystyrene Nanofibers and 1-D Nanolens Array Fabrication

We demonstrate here that the dewetting in a solvent-non-solvent mixture can be employed to achieve a facile, rapid and lithography-free fabrication of well-aligned nano to microscale 1-D polymer droplet arrays from electro-spun polystyrene (PS) nanofibers. We observed a Rayleigh-instability-driven morphological transition when thermally annealed electrospun PS fibers on a silanized glass substrate were dewetted with a solvent-water media. Instability in PS nanofibers is affected by the interactions occurring between the polymer and the substrate beneath it. We demonstrated that the dewetting kinetics and morphology of dewetted structures depends on whether dewetting is induced by thermal annealing, exposure to solvent vapor, or immersion in a liquid media of solvent and non-solvent. Intensified dewetting in liquid media not only results in significantly faster dewetting dynamics but also results dewetting of thicker nanofibers, which remain stable under thermal annealing or solvent-vapor exposure. Moreover, the droplets produced by this method have significantly higher aspect ratio and can be used as nanolenses in super resolved microscopy. The number density of nanolenses can be increased beyond any limit by sequential dewetting of nanofibers in the liquid mixture of MEK-water to attain more closely packed lens arrays which cannot be achieved by the dewetting of thin films. This provides a promising approach for fabricating aligned and densely packed polymer structures with controllable sizes ranging from nano to micro length scales.