Fabrication And Regulation Of Superhydrophobic Wood Surfaces Via Migration Driven By Vapor Method

As one of renewable resource,wood features high strength and toughness,perfect rigidity,good workability.However,there is a fatal defect for wood that it easily absorbs water or moisture when exposed to ambient conditions,especially in alternating damp-heat environments.Because of these undesired properties,wood is susceptible to crack,mildew,decay and degrade,thus limiting its performance in real-life applications.In spired by nature,fabrication of superhydrophobic surface on wood is considered as one of promising method to enhance its water repellent property and improve its other properties e.g.,self-cleaning function,thermal stability,anti-corrosion ability.Up to now,many methods have been proposed to prepare superhydrophobic surfaces.However,there are still some challenges for their practical application e.g.,harsh processing conditions,complex procedures,poor interfacial adhesion.Therefore,a novel method of migration driven by vapor method using commercial nanosilica particles and vinyltriethoxysilan(VTES)was firstly proposed in this paper.Specifically,nanosilica particles became hydrophobic and grew into micro-level size after modified by VTES.Driven by vapor pressure,these hydrophobic particles were randomly transferred and arranged on wood surface,leaving nano/micro cracks and thus forming the hierarchical rough structure.The strong vapor pressure enables the superhydrophobic coating with enough thickness,thereby enhancing its mechanical stability.Finally,durable superhydrophobic wood was obtained via a simple method.The main results can be summarized as follows:(1)After modified by nanosilca particles and VTES,the hydrophilic wood with contact angle of 60° became superhydrophobic with contact angle of 154° and sliding angle of-0°.The surface morphology and chemical structure was studied using scanning electron microscopy and X-Ray diffraction.The results show the nanosilica particles modified by VTES grew into micro level size and randomly dispersed on the wood surface,leaving abundant of nano/micro cavities,which endow the as-prepared sample with hierarchical structure that mimics to lotus leaf.(2)The effect of different factors on creation of superhydrophobic structure was studied,and the results indicate the amount of alkali and the ratio of nanosilica and VTES were the most influential element;The optimized parameters for preparing superhydrophobic surface on wood of both the radial and cross sections was:1.5 h deposition time,100 ℃(140℃ for cross section)deposition temperature,0.5 ml/cm2 adoption of solution,12 ml alkali,SiO2 and VTES with ratio of 1:1;The two sections show almost the same regular on wettability when superhydrophobic coating was created on their surface.However,there is a significant difference between the two sections:the superhydrophobic coating in transection shows more transparency than that of radial section.(3)Based on the investigation of influential elements,the mechanism of fabricating superhydrophobic surface can be described as follows:nanosilica particles serves as skeleton material to create the roughness.Vinyltriethoxysilan serves as both the low-surface-free-energy modifier for nanosilica particles and essential hinder to prevent these particles to form serious agglomeration.Sodium hydroxide offers a suitable condition for the hydrolyzation and polymerization of vinyltriethoxysilan.Thus,the hydrolyzed vinyltriethoxysilan can react with nanosilica and grow on nanosilica particles surface.The modified nanosilica particles with micro-level size became hydrophobic.The arrangement of hydrophobic particles on wood surface left abundant micro/nano cracks.The hierarchical rough structure was created by the hydrophobic nanoparticles and micro/nano level cracks.Moreover,the introduce of sodium hydroxide endow wood surface with more active hydroxyl groups,which in consequence ensure enough hydrophobic nanosilica particles to graft on wood substrate.(4)The durability of superhydrophobic surface was tested systematically,the results show that the as-prepared sample can suffer severe abrasion including sandpaper abrasion length of 1050 mm under pressure of 3000 Pa,sandpaper abrasion length of 150 mm under pressure of 12,000 Pa,and repeatedly abrasion by a knife;the superhydrophobic surface can retain its property after immersion in acid/alkali for 25 h,in sea water for 15 h;the water droplet with temperature of 0～100℃ all can be well supported by superhydrophobic surface in spherical shape.Simultaneously,the as-prepared surface can suffer hot water boiling for 3 h.Moreover,the superhydrophobic coating can protect wood from thermal degradation;the self-cleaning ability of the obtained wood can effectively remove dirt on its surface.