Fabrication Of Superhydrophobic Wood Surfaces Via Sol-gel Process And The Structure And Properties

Fabrication of superhydrophobic surfaces on wood substrate can inhibit the invasion of liquid water and thereby avoid dimensional instability and fungal degradation related to water absorption. Based on the lotus effect, superhydrophobic wood surfaces were fabricated with silica nanoparticles and low-surface-energy materials through the sol-gel process. The main contents and results are as follows:1. Highly hydrophobic wood surfaces were produced based on a two-step process consisting of growing nanofilms on the wood substrate(Chinese fir) with silica sol followed by hydrophobization with hydrolyzed hexadecyltrimethoxysilane(HDTMS) based on the St?ber method. The microstructure and chemical composition of the coatings were examined by fieldemission scanning electron microscopy(FE-SEM), energy dispersive X-ray analysis(EDXA) and FTIR spectroscopy. Hydrophobicity of the treated wood was evaluated by water contact angle(CA) measurements. The results show that spherical nanoparticles with diameter of about 50 nm were deposited uniformly on the wood surface, and the long-chain hydrophobic HDMTS was covalently linked to the surface of silica particles. The elevated hydrophobicity of wood was manifested by the water CA of about 150° on the transverse surface, but only 141° on the longitudinal surface with the formed nanoparticles distributed uniformly without aggregation to larger roughness.2. Superhydrophobic nanocoatings were fabricated on the intrinsically heterogeneous surfaces of wood using silica-polymer hybrid materials, which were prepared through sol-gel chemistry using tetraethoxysilane(TEOS) as an inorganic precursor and HDTMS as an organic modifier. The microstructure and chemical composition of the siliica nanoparticles were examined by transmission electron microscope(TEM) and FTIR spectroscopy. The microstructure and morphology of the coatings on wood sufraces were examined by FE-SEM. Hydrophobicity of the treated wood was evaluated by CA measurements. The long-chain HDTMS acts not only as a hydrophobic agent to lower the surface free energy of the silica particles but also as a bonding agent to aggregate the nanoparticles by polymerization. The degree of aggregation of the silica nanoparticles in the coating can be controlled by adjusting the initial concentration of HDTMS, and hence the surface morphology and roughness of the coated wood are tuned. When the concentration of HDTMS reaches a critical level, the formed aggregates of silica particles in combination with the inherent microscale roughness of wood appear to create hierarchical micro/nanostructures on the wood substrate, allowing for generation of superhydrophobicity. The silica-polymer hybrid coatings on wood surfaces are robust enough to withstand high humidity as well as strong acid and alkali whilst retaining its superhydrophobicity.3. Superhydrophobic coatings with robust mechanical stability were successfully fabricated on the intrinsically heterogeneous wood substrates by simply dip-coating the suspensions of hydrophobic silica(SiO2) nanoparticles dispersed in polydimethylsiloxane(PDMS) solution. The microstructure and chemical composition of the siliica nanoparticles were examined by TEM and FTIR spectroscopy. The microstructure and morphology of the coatings on wood sufraces were examined by FE-SEM and atomic force microscope(AFM). Hydrophobicity of the treated wood was evaluated by CA measurements. The surface microstructure, roughness and wetting behavior of the PDMS/silica hybrid coatings on wood surfaces were investigated in relation to the loadings of the silica particles in the PDMS matrix. When the silica particle loading reaches a critical level, desirable hierarchical micro/nanostructures are formed on the wood substrate, allowing for the generation of superhydrophobicity with a contact angle of 152° and a sliding angle less than 10°. The fabricated PDMS/silica hybrid coating exhibits remarkable durability against mechanical abrasion and high-frequency ultrasonic washing in water whilst retaining its microstructure and superhydrophobicity.