Porous Spindle-Knot\nFiber by Fiber-Microfluidic Phase\nSeparation for Water Collection and Nanopatterning

Porous spindle-knot structures have been found in many\ncreatures,\nsuch as spider silk and the root of the soybean plant, which show\ninteresting functions such as droplet collection or biotransformation.\nHowever, continuous fabrication of precisely controlled porous spindle-knots\npresents a big challenge, particularly in striking a balance among\ngood structural controllability, low-cost, and functions. Here, we\npropose a concept of a fiber-microfluidics phase separation (FMF-PS)\nstrategy to address the above challenge. This FMF-PS combines the\nadvantages of a microchannel regulated Rayleigh instability of polymer\nsolution coated onto a fiber with the nonsolvent-induced phase separation\nof the polymer solution, which enables continuous and cost-effective\nproduction of porous spindle-knot fiber (PSKF) with well-controlled\nsize and porous structures. The critical factors controlling the geometry\nand the porous structures of the spindle-knot by FMF-PS have been\nsystematically investigated. For applications, the PSKF exhibited\nfaster water droplet nucleation, growth, and maximum water collection\ncapability, compared to the control samples, as revealed by in situ\nwater collection growth curves. Furthermore, high-level fabrics of\nthe PSKFs, including a two-dimensional network and three-dimensional\narchitecture, have been demonstrated for both large-scale water collection\nand art performance. Finally, the PSKF is demonstrated as a programmable\nbuilding block for surface nanopatterning.