Non-Close-Packed Breath Figures via Ion-Partitioning-Mediated Self-Assembly

We report a one-step method of forming non-close-packed (NCP) pore arrays of micro- and sub-micropores using chloroform-based solutions of polystyrene acidified with hydrogen bromide for breath figure (BF) patterning. As BF patterning takes place, water vapor condenses onto the polystyrene solution, forming water droplets on the solution surface. Concurrently, preferential ion partitioning of hydrogen bromide leads to positively charged water droplets, which experience interdroplet electrostatic repulsion. Self-organization of charged water droplets because of surface flow and subsequent evaporation of the droplet templates result in ordered BF arrays with pore separation/diameter (L/D) ratios of up to 16.5. Evidence from surface potential scans show proof for preferential ion partitioning of HBr. Radial distribution functions and Voronoi polygon analysis of pore arrays show that they possess a high degree of conformational order. Past fabrication methods of NCP structures typically require multi-step processes. In contrast, we have established a new route for facile self-assembly of previously inaccessible patterns, which comprises of only a single operational step.