Direct imaging of polymer filaments pulled from rebounding drops

TL;DR

This paper introduces a straightforward technique to create and analyze stretched polymer filaments by impacting drops on superhydrophobic surfaces, revealing new insights into filament formation and potential applications in biology and materials science.

Contribution

The study demonstrates a novel method for depositing stretched polymer fibers using drop impact dynamics on microstructured surfaces, with detailed characterization of filament formation.

Findings

Impacts on superhydrophobic surfaces produce stable polymer filaments.

Filament formation depends on impact velocity, substrate structure, and polymer concentration.

Raman spectroscopy confirms the presence of stretched DNA filaments.

Abstract

Polymer filaments form the foundation of biology from cell scaffolding to DNA. Their study and fabrication play an important role in a wide range of processes from tissue engineering to molecular machines. We present a simple method to deposit stretched polymer fibers between micro-pillars. This occurs when a polymeric drop impacts on and rebounds from an inclined superhydrophobic substrate. It wets the top of the pillars and pulls out liquid filaments which are stretched and can attach to adjacent pillars leaving minuscule threads, with the solvent evaporating to leave the exposed polymers. We use high-speed video at the microscale to characterize the most robust filament-forming configurations, by varying the impact velocity, substrate structure and inclination angle, as well as the PEO-polymer concentration. Impacts onto plant leaves or randomized nano-structured surface leads to the formation of a branched structure, through filament mergers at the free surface of the drop. SEM shows the deposition of filament bundles which are thinner than those formed by evaporation or rolling drops. Raman spectroscopy identifies mode B stretched DNA filaments from aqueous-solution droplets.