Rinse-Resistant Superhydrophobic Block Copolymer Fabrics by Electrospinning, Electrospraying and Thermally-Induced Self-Assembly
An inherent problem that restricts the practical application of superhydrophobic materials is that the superhydrophobic property is not sustainable; it can be diminished, or even lost, when the surface is physically damaged. In this work, we present an efficient approach for the fabrication of superhydrophobic fibrous fabrics with great rinse-resistance where a block copolymer has been electrospun into a nanofibrous mesh while micro-sized beads have been subsequently electrosprayed to give a morphologically composite material. The intricate nano- and microstructure of the composite was then fixed by thermally annealing the block copolymer to induce self-assembly and interdigitation of the microphase separated domains. To demonstrate this approach, a polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) nanofibrous scaffold was produced by electrospinning before SEBS beads were electrosprayed into this mesh to form a hierarchical micro/nanostructure of beads and fibers. The effects of type and density of SEBS beads on the surface morphology and wetting properties of composite membranes were studied extensively. Compared with a neat SEBS fibrous mesh, the composite membrane had enhanced hydrophobic properties. The static water contact angle (CA) increased from 139° (±3°) to 156° (±1°), while the sliding angle decreased to 8° (±1°) from nearly 90°. In order to increase the rinse-resistance of the composite membrane, a thermal annealing step was applied to physically bind the fibers and beads. Importantly, after 200 h of water flushing, the hierarchical surface structure and superhydrophobicity of the composite membrane were well retained. This work provides a new route for the creation of superhydrophobic fabrics with potential in self-cleaning applications (Fig. 1).
Fig.1 A schematic illustration of the fabrication process of rinse-resistant superhydrophobic fabrics.
Based on previous study（Macromol Rapid Comm, 2015, 36,1437.）, SEBS/THF solution could be electrospun to from fibers and beads with 8-20wt%. The surface morphology can be affected by air humidity (Fig. 2). Bead density has a great effect on the overall surface roughness of composite membranes. The SEM micrographs reveal that beads were stacked on the fibers, and the SEBS composite membranes possessed a hierarchical micro/nanostructure.
Fig 2. SEM images and contact angles of SEBS composite membrane with different bead density
It appears that the increase in surface roughness arising from incorporation of beads is the main reason for the observed improvements in superhydrophobicity (as shown in Fig. 3). SEM revealed that the beads that stacked on the untreated composite membranes were removed after water flushing for 200 h, and only a few beads were retained on the fibrous surface. This vast reduction in bead density explains the observed transformation in the membrane’s wettability and superhydrophobicity.
Fig. 3. SEM images and contact angles of the untreated and thermally annealed SEBS composite.
In Conclusion, commercially available Kraton triblock copolymer (SEBS) composite membranes, which consist of fibers and beads, were successfully fabricated by electrospinning and electrospraying. The introduction of beads successfully increased the static water contact angle of the composite membrane, whilst decreasing the sliding angle dramatically, characteristic of a superhydrophobic material. After thermal annealing, the composite membrane maintained its superhydrophobicity with physical cross-links between the fibers and beads providing structural integrity, and displayed excellent flush resistance due to the stabilized composite structure.
The study has been published at Applied Surface Science, 2017, 422, 769-777. The first author is Master Student Jie WU (South China University of Technology). The Corresponding authors are Prof. Linge WANG (AISMST, South China University of Technology) and Prof. Paul D. TOPHAM (Aston University).
Source from South China Advanced Institute for Soft Matter Science and Technology