Design And Preparation Of Multifunctional Superhydrophobic/superamphiphobic Coatings And Their Applications

Wettability is considered as one of the most important surface properties of solid materials,which generally depends on two essential features,surface roughness and chemical compositions.Because of the low adhesion,superwetting surfaces,such as superhydrophobic and superamphiphobic surfaces,have wide applications in chemical engineering and ordinary life.Various approaches have been exploited to create micro-/nano-structures,preparing a series of superwetting surfaces.However,requirement of sophisticated instruments,complicated procedures,dependent substrates as well as poor mechanical and chemical robustness severely hinder development of the superwetting surfaces.Moreover,besides low adhesion ability,how to endow materials with more functionality is still a challenge.In this dissertation,by elaborate design and creation of hierarchically micro-/nano-scale surface structures using micro-/nano-particles and low surface energy materials,a new strategy to construct multifunctional superwetting surfaces with good durability and mechanical robustness is proposed;the as-prepared coatings can be applied to various substrates including plastic film,rubber and textiles,realizing their superhydrophobicity/superamphiphobicity and multifunctional practical applications.The main contents and results are as follows:1.A fluorine-free superhydrophobic coating with high durability is prepared based on dimethyloctadecyl [3-（trimethoxysilyl）propyl] ammonium chloride（QAS）functionalized silica nanoparticles and thermoplastic elastomer polystyrene-bpoly（ethylene-co-butylene）-b-polystyrene（SEBS）.The effects of solvent etching on the surface micro-nano structure and the wettability are investigated.The weatherability,mechanical properties and multiple functions of the as-prepared superhydrophobic surface are discussed.Results show that the hydrophobic nanoparticles are exposed and the surface roughness is improved after removing the surficial SEBS by the solvent-etching treatment,thereby the surface wettability is regulated.When the etching time is set above 2 min,a superhydrophobic surface which can resist the wetting and erosion of water stream is obtained.Due to the highly hydrogenated structure and high adhesion of the rubber adhesive on the matrix,the as-prepared superhydrophobic surface can well resist different mechanical/chemical/physical treatments（including strong acid/alkaline,high（200℃）/low temperature,UV irradiation,120 g sand-/50-cycle sandpaper-abrasion,50-cycle tape-peeling and 500-cycle scrubbing）without destroying the surface structures or losing the anti-wetting property,showing strong robustness.Notably,even under large stretching（500%）or bending deformations,such surface still displays stable superhydrophobicity,as a result of the increased surface roughness.Such multifunctional superhydrophobic coating can be applied for various substrates including PET film,copper foil,printing paper,wood and fabric,and multiple functions such as self-cleaning,oil/water separation and antibacterial property can be realized.2.In the above studies,it is found that the surface morphology and roughness can be influenced by the deformations of substrates,which provides a way to regulate the surface wettability by stretching.In this work,a coating material is prepared from a thermoplastic elastomer and hydrophobic SiO₂ nanoparticles,and the surfaces with different wettability have been constructed by spray-coating such material onto prestretched rubber substrates.The rebounding of pre-stretched rubber substrate can help to construct micro-wrinkle structures of the surface,forming the superhydrophobic surface with stretch-controllable wettability.The effects of the pre-stretching strains of the rubber substrate on the surface micro-nano structure and wettability are studied.Results show that the surface geometric parameters and dimensionless spacing factor（Sf）can be adjusted by controlling the pre-stretched deformation of the rubber substrate,thereby regulating the surface wetting state.When the pre-stretching strains increases from 0% to 200%,the value of Sf2 changes,presenting the transition of the wetting states from hydrophobic Wenzel state to superhydrophobic Cassie state.Such superhydrophobic surface with stretch-controllable wettability can realize the realtime reversible and cyclic transformation of Wenzel state to Cassie state when adjusting the stretching strains from 0% to 200%.Such interesting surfaces can be applied for transportation of bubbles underwater.3.In order to regulate of surface wettability by changing the surface chemical structure,a novel fluorine-free pH-responsive coating is prepared by using QAS/（N,N-dimethyl-3-aminopropyl）trimethoxysilane（DMAPS）-modified SiO₂ nanoparticles and polyethylene imine（PEI）as the roughness building element and binder,respectively.The effects of pH value on the surface chemical structure and the wettability are investigated.The weatherability,mechanical properties and multiple functions of the as-prepared superwetting surface are explored.The created surfaces become superhydrophilic and underwater superoleophobic after acid-treatment while turn to be superhydrophobic and superoleophilic after base-treatment,attributing to the protonation and deprotonation of the tertiary amine group which is adjusted by pH value.The surface has high resistance to chemical corrosions（strong acid/base solutions and various organic solvents）and mechanical abrasions（50-cycle mechanical abrasion and 120-cycle tape-peeling）.Such coating can be used for different porous substrates,e.g.cotton fabric and filter paper,to develop multifunctional separation materials having the properties of self-cleaning,antibacterial,tunable superhydrophilicity/superhydrophobicity,and the coated porous materials can effectively separate various types of oil/water mixtures.4.Based on the above works on constructing the multifunctional superhydrophobic surface,a surface that has hierarchically overhanging re-entrant structures and super-repellency to water and oils is constructed using micro-sized ammonium polyphosphate particles（APP）,functionalized SiO₂ nanoparticles（MSi）and fluorinated alkyl silane.The effects of MSi/APP mass ratios on the surface roughness and the wettability are investigated.The dependence of the wettability of water and oil on the surface with hierarchical roughness is theoretically investigated,and the superamphiphobic mechanism is analyzed.The chemical stability,mechanical properties,weatherability,flame-retardant properties and multiple functions of the asprepared superamphiphobic surface are discussed.The surface roughness（Ra）of the resultant super-repellent surface is adjusted by varying the mass ratios of MSi and APP.A randomly overhanging re-entrant structure with Ra = 3.13 μm is obtained when the MSi/APP mass ratio is 2:3,acquiring a superamphiphobic surface with excellent repellency towards a broad range of liquids having surface tension of26.6⁸9.7 m N/m.The created superamphiphobic surface demonstrates extremely high stability under exposure to strong corrosive chemicals（namely aqua regia,concentrated sulfuric acid and sodium hydroxide）,cyclic mechanical abrasions,UV irradiation,and heat treatment.Such coating can be applied for a wide range of substrates including PET film,Cu mesh,wood,and fabric,enabling super-repellency to water and oils with low surface tensions.More importantly,the superamphiphobic coating offers greatly suppressed flame propagation to cotton fabrics,and the coated cotton fabric can self-extinguish after 12 s-ignition,leaving an intact fabric with less than 8-cm char layer and showing high flame-retardant performance.5.To solve the problem of environmental pollution caused by the heavy use of volatile organic compounds in preparing superamphiphobic surface,a robust waterborne superamphiphobic coating,consisting of micro-sized APP particles,SiO₂ nanoparticles,fluorocarbon surfactant and fluorinated alkyl silane,is constructed using water as a green solvent.The effects of the chemical structures and cooperation of the components of the coating materials on the surface roughness and wettability are investigated.The theoretical simulations regarding the effect of the surface structures on wetting stability are performed.The weatherability,mechanical properties and multiple functions of the as-prepared surface are explored.Results show that the amphiphilic structure of fluorocarbon surfactant allows the well dispersion of the coating materials in water,and the fluorinated alkyl silane can lower the surface energy of the coating.The cotton fabric coated by such waterborne superamphiphobic coating displays super-repellency to a variety of liquids including dodecane with a low surface tension of 24.3 m N/m.Micro-sized APP,nano-sized SiO₂ particles in conjunction with the fabric texture synergistically form a multi-tier micronano structure,which improves the surface roughness,thereby enhancing the superamphiphobic stability.The values of calculated robustness ratio,A*,of the coated fabric for water and hexadecane are 22.72 and 7.11,respectively,which are much higher than the critical value（1）,indicating the as-prepared surface shows stable superamphiphobicity.The experimental results are in good agreement with the theoretical ones.The as-prepared superamphiphobic surface shows good weatherability and mechanical robustness,showing high resistance to strong acid,high-salinity brines,UV irradiation,high temperature,50-cycle sandpaper-abrasion without damaged surface hierarchical structures or decreased anti-wetting property.The coated cotton fabric self-extinguishes after 12 s-ignition,leaving an intact fabric with less than 8-cm char layer,and multiple functions such as self-cleaning and antifouling are realized.6.Based on the above works,the multifunctional superamphiphobic coating described in the chapter 5 is applied for protective clothing to improve protective performances.The effects of the hierarchically micro-/nano-scale surface structures on the wettability and protective performances are investigated.Results show that the superamphiphobic coating can be applied for cotton,polyester,viscose fiber and polypropylene non-woven fabrics,offering substrate-independent super-repellency to various liquids including water,synthetic blood and edible oil with CAs greater than 150°and SA lower than 10°.Synthetic blood can easily roll off from the surface of coated fabric without leaving any residual.Due to the presence of QAS,the coated fabric shows the excellent antibacterial activities with an efficiency up to 100%against two typical bacterial,gram-negative E.coli and gram-positive S.aureus.The special hierarchically micro/nano morphology can provide high roughness that is helpful for trapping air at the solid-liquid interface,forming a durable superamphiphobic surface and improving the resistance to penetration by water and synthetic blood.The protective performances of ordinary protective clothing are improved by using the superamphiphobic coating,meeting the technical requirements for single-use protective clothing for medical use（GB 19082-2009）,that is,the level of spray rating ≥ 3,moisture permeability ≥ 4000 g/（m².d）,water pressure resistance≥ 20 Kpa,filtering efficiency ≥ 99%,the level of resistance to penetration by synthetic blood = 6,and electrostatic charge decay ≤ 0.05 s.