Dual Conical Fibers for Controllable Liquid Transfer

Solution processes, especially those using open systems, have shown advantages of mild conditions, cost-effectiveness, and broad substrate compatibility in making micro-patterned functional films of optoelectronic devices. Owing to the extreme dynamics of liquids, finely controlling liquid transfer remains largely unsolved, particularly across dimensions from μm- to cm-scale. Here, we propose a model structure of dual conical fibers (dual-CFs) that enables liquid transfer to proceed in a well-controllable manner for micro-patterning. The critical structural parameters for fully holding liquid within dual-CFs are clarified, and quantitative correlations between fiber topology and steady liquid transfer are established. The dual-parallel-fibrous structure, representing the minimum number of CFs for the structure model, helps suppress Plateau–Rayleigh instability by virtue of the confined noncircular cross-sectional liquid film; while the conical structure enables effectively holding liquid, without any leakage during the transfer process, due to the as-generated Laplace pressure difference. The dual-CFs benefit from minimizing the rupture energy of the liquid film by the minimal cross-sectional area confined at the tips, which leads to finely anchoring the three-phase contact line. As a synergistic consequence, liquid can be transferred onto substrates in a controllable manner, resulting in micro-patterns with well-defined profiles. More importantly, the model structure of dual-CFs can be programmably arranged into multi-conical fiber arrays, by which direct-writing micro-patterns from μm-scale microlines to cm-scale uniform films can be realized. The direct-writing strategy is applicable for making functional micro-patterns, offering inspiration for micro-patterning liquid materials using fibrous open systems.