Bio-inspired Materials with Special Wettability for Oil-Water Separation and Underwater Adhesion

基於特殊潤濕仿生材料的油水分離和水下粘附的研究

Student thesis: Doctoral Thesis

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Award date12 Jun 2017

Abstract

The development of interfacial materials with special wettability that mimic the innate functionalities of nature will have significant impact on the energy, environment and global healthcare. Thanks to the rapid advancement in micro/nano fabrication technology, it is possible to synthesize artificial materials with desired size, composition and wettability. Over the past decades, interfacial materials with special wettability such as superhydrophobic surfaces (SHS) have been extensively studied for practical applications including non-wetting textiles, anti-frost/icing material coatings, oil-water separation membranes and anti-biofouling medical devices. Despite extensive progress made in the study of interfacial materials with special wettability, their applications are mainly limited in dry conditions. The design and fabrication of interfacial materials with special wettability in wet environment is a challenging yet highly rewarding endeavor that contributes to the conservation of marine environment. The objectives of this dissertation are to develop novel structured materials with special wettability even in wet environment using the bio-inspired approach for oil-water separation, anti-biofouling, and underwater adhesion applications.

In the first part of this dissertation, I present the developing of a novel composite membrane with for multifunctional applications. By tailoring the surface structure, chemical composition, and harnessing the synergistic cooperation of non-adhesion nature of polyethylene glycol (PEG) and silver nanoparticles embedded in the PEG matrixes (PEG-Ag NPs membrane), the designed membrane allows for high oil-water separation efficiency (>99.9%) in a wide range of operating conditions, as well as enhanced antimicrobial and anti-marine fouling activities. It is anticipated that the facile fabrication and multifunctional performances will bring this membrane a step closer to practical applications including the clean-up of oil spills, waste water treatment, fuel purification, and the separation of commercially relevant oil-water emulsions.

In the second part of my dissertation, I investigated the separation of surfactant free and surfactant-stabilized water-in-oil emulsions containing nanometer sized oil/water droplets. Via electrospinning technique, superhydrophobic and superoleophilic PH-CNT membrane was fabricated, and carbon nanotube (CNT) was incorporated into the electrospun membrane by a nozzle. The incorporation of CNT was simple but effective to improve the hydrophobicity of the membrane. The films with thickness in micrometer scale can be utilized to separate both surfactant-free and surfactant-stabilized water-in-oil emulsions with high separation efficiency (> 99.5 wt% in terms of oil purity in the filtrate), in addition, the separation flux is up to 360 l m-2 h-1, which is several times higher than commercial filtration membranes with a similar oil-water separation performance.

Finally, switchable underwater adhesion activated by the interfacial screening effect of smart polymers was investigated. The thermoresponsive underwater adhesive which entails the reversible, tunable and fast regulation of the wet adhesion on diverse surfaces was fabricated by free radical polymerization. The adhesive synergistically takes advantage of the supramolecular host-guest interaction, catechol chemistry and thermoresponsive wettability, allowing for the on-demand rectification of wet adhesion simply by the local temperature trigger. The adhesive is versatile, switchable and fast in the aqueous surrounding. This work represents an important paradigm in the design of smart underwater adhesive, but could stimulate new thinking for the rational design of bio-inspired materials with performances far beyond nature.