| Polyurethane (PU) with excellent properties and tailorable molecular structure has been paid much significance as one of the most versatile materials. The comprehensive applications of PU ranged from coatings, adhesives, foams and elastomers to some functional materials including biomaterials, separation membranes and shape memory materials etc. With regard to a variety of PU materials, the wettability on surface is always of critical importance for adapting themselves to the varying circumstances and improving their functions. The surface wettability is closely associated with some specific properties like antifouling behaviors of coatings, surface biocompatibility of biomaterials, water permeability of membranes, etc.Fluorine-containing compounds with low surface tension and friction coefficient play an important role in fabricating superhydrophobic surface (water contact angle, WCA>150°). The introduction of fluoro-units into PU materials is always regarded as one of the most effective ways to prepare superhydrophobic PU. However, for the surface-fluorination of PU materials, the post-treatment on the surface of as-prepared materials was cumbersome and sometimes costly especially for massive production. On the other hand, the bulk-fluorination of PU, which was realized mainly through the incorporation of fluoro-units into PU’s soft segments, hard segments, chain extenders and end-capping structures, often encountered low content or even depletion of fluorine on surface, which hindered the participation of fluoro-units in improving surface wettability. Accordingly, it is necessary to design and fabricate specific molecular structure of PU to facilitate the fluorine-enrichment on surface in favor of superhydrophobicity.In addition to the hydrophlicity/hydrophobicity, the adhesion of water droplet on surface is also an unavoidable aspect of surface wettability. Two distinct superhydrophobic phenomena in nature, namely "lotus effect" with low adhesion to water and "petal effect" with high adhesion to water, have been well-known. Evidently, compared with the comprehensive and intensive studies of the artificial self-cleaning surfaces, the investigation of the artificial superhydrophobic surface with high adhesion was initiated just several years ago. Actually, the biomimetic surface bioinspired by rose petal has been verified to possess the capacity of manipulating the water droplet transfer without mass loss promising for its applications in fluidic devices. At present, the reported fabricating methods for this sort of surface mainly included replication of natural and artificial templates, surface-etching, surface deposition and self-assembly, plasma-processing, etc, some of which were inappropriate for massive production. Therefore, it is necessary to further explore more convenient approaches to fabricate the superhydrophobic surface with high adhesion.In this study, a fluorinated hyperbranched pory(urea-urea-urethane)(HBPU) nanofibrous membrane was prepared. HBPU was first modified at its hydroxyl end groups with2-bromoisobutyryl bromide to obtain a macroinitiator, which further initiated the atom transfer radical grafting polymerization (ATRgP) of a fluorine-containing monomer. The nanofibrous membrane of fluorinated HBPU was prepared by electrospinning. The structure of polymers was characterized by fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectrum (NMR). The surface of nanofibrous membrane was investigated with scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) analysis, respectively. The results suggested that compared with the reported linear fluorine-containing polyurethane materials, a rather high fluorine-content up to29.14%on the surface of fluorinated HBPU nanofibrous membrane was achieved. Moreover, a superhydrophobic surface (WCA159.7°) with high adhesion to water was successfully fabricated via a convenient electrospinning method. |
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