Correcting misconceptions in wettability theory and utilizing fluid surface tension to create complex hierarchical polymer structures
Nanoimprinting with anodized aluminum membranes was performed to produce nanoposts with controlled diameter and aspect ratio. The polymer nanoposts were found to remain upright and preserve the post-packing structure at low aspect ratios, but succumbed to elastocapillary coalescence at higher aspect ratios, with the morphology of the aggregates directly related to the aspect ratio of the polymer nanoposts. Replication of the replicated nanoposts at low aspect ratio was achieved to reproduce the pore packing structure of the original alumina membrane.
Teflon microparticles were found to be effective stabilizers for inverse foams, producing dry water with excellent flow properties and contact stability and consisting of non-spherical liquid marbles 90-500 microns in diameter. The chemical inertness of the PTFE particles allowed for use of not only water, but also aqueous solutions of acids and bases and organic molecules including ionic liquids and water-soluble polymers. The teflon particle shell stabilized the liquid drop such that two particles containing two solutions which would ordinarily mix and/or react would remain separate.
The wettability studies focused on demonstrating that entrapped gases are not responsible for Cassie superhydrophobic wetting behavior, that the removal of the pockets of air would not lead to Wenzel wetting behavior with an increase in contact angle hysteresis. The measurement of advancing and receding contact angles on surfaces with controlled topography consisting of square posts holes showed that the contact angles remained unchanged despite removal of over 90% of the air. It showed that water was not intruding into the hydrophobic topography because the Laplace pressure was thermodynamically preventing water from increasing its interaction with the topographically-patterned surface. Wettability studies were also aimed at extending our understanding of wettability as a one-dimensional phenomenon from the three-phase contact line perspective, by investigating the ability of hydrophilic arcs, short and long wedges, and the outlines of the wedges, to pin water drops on hydrophobic, low hysteresis surfaces. They were additionally aimed at studying the ability of hydrophilic lines to deform the three-phase contact line of a water drop and kinetically trap a water drop in a distorted shape on a hydrophobic surface.