Function-led design of multifunctional stimuli-responsive superhydrophobic surface based on hierarchical graphene-titania nanocoating

Abstract

With the advancements in both nanotechnology and micro-fabrication techniques, the development of superhydrophobic surface (SHS) enters a new era which highlights the significance of multifunctionality, tunable surface property, and smart response. Novel multifunctional SHS may accomplish multiple tasks simultaneously in real-field applications while tunable surface property can effectively induce smart responses on the SHS, which further benefit the functional optimization, life cycle, and prompt the total system efficiency of SHS. Based on the clear understanding of the application requirement and the material property, function-led design of SHS can be realized so that high performance SHS are achieved with reduced cost and optimized functions. In order to fabricate SHS with highly interactive interfacial dynamics, graphene, one of the thinnest among the existing materials, was chosen and applied to the flexible textile fabrics. Extremely strong bonding was observed between graphene and the fibers, and the thin sheets of graphene were also observed to tightly wrap according to the surface profiles of the fibers. Surprisingly, the hydrophilic cotton fabric became hydrophobic with a graphene loading of only 0.5 wt%. By further upgrading the monolayer graphene coating on the fabric, a nanofilm of titania (TiO₂) was subsequently applied onto the graphene surface which created a hierarchical surface structure showing superhydrophobicity. As a result of the photoactivity of TiO₂, UV-triggered superhydrophilic conversion can be readily achieved on this novel SHS. Enhanced control over the conversion rate and the wettability were also achieved due to the interfacial charge transfer interaction between TiO₂ and graphene. Tunable adhesion, spreading, and transport of water droplets can be realized on the as-obtained hierarchical graphene-TiO₂ (GT) SHS, which can further transform the GT-SHS into a versatile platform for micro-droplet/fluid manipulation. Multiple functions of application significance, i.e.directional water transport, micro-droplet storage and transfer, self-cleaning and gas sensing, are readily demonstrated on GT-SHS; exceptional oil/water separation performance is also shown by the membrane based on GT-SHS. Therefore, potent potential in the sweat and moisture management of quick-dry garment, micro-volume droplet storage, and oily water treatment can be anticipated for the novel stimuli-responsive GT-SHS. To speak further, being perceived as an essential bridging step between the fundamental research and practical application, the function-led design criterion can be envisaged as the new guiding code for the research and development of SHS.