Preparation And Protective Mechanism Of Long-term Coating With Super Liquid Repellency

Adsorption and adhesion of liquid substances,such as water and oils,will reduce the use efficiency and service life of materials,causing surface contamination and health and safety risks.And frequent replacement of materials or surface cleaning can increase work tasks and practical costs.For this kind of problem,coating technology is one of the most convenient and economical protection approaches at present,among which the nano-coating with super liquid repellency is the focus of researches in related fields at home and abroad.Due to the high contact angles over 150°and roll-off angles below 10°on the surface with super liquid repellency,water or oil drops on the coating can easily fall off,with no adsorption and adhesion.The protected material can efficiently keep the original functional properties for a long time,achieving the purpose of cost reduction and efficiency increase.In this paper,the super-liquid-repellent coatings with specific protective properties have been designed and prepared for the two typical application problems of moisture absorption on activated carbon（AC）and oil contamination on range hood parts.Functional nanoparticles were coated on the surface of AC to form superhydrophobic surfaces.Then the waterproof and moisture-proof properties,water vapor condensation and water droplet impact rebound properties on superhydrophobic coatings were studied,revealing the long-term stability mechanism and the selective adsorption behavior under different conditions.Meanwhile,superamphiphobic coatings for range hood application was investigated,exploring the chemical stability under organics immersion and protection mechanism induced by dense modified structure.The physical stability of the coatings was strengthened through the phase separation caused by the introduction of inorganic binder.Based on the nano mechanical properties,the system analyses on mechanical abrasion resistance and environmental durability were conducted,revealing the self-healing mechanism to maintain super-liquid-repellency.The multi-dimensional applications of super-liquid-repellency protective coating are realized,presenting broad development prospects.The main results are divided into the following aspects:（1）The fluorous superhydrophobic nanoparticles were coated on the surface of AC porous adsorption materials by rotary evaporation process,constructing the superhydrophobic surface with typical multi-level structure.The weight increment of the coated AC was 13.3%in high humidity environment for 400 min,achieving 73.4%enhancement on moisture-proof property and good permeability against original AC.In the adsorption experiments on ethanol/water mixture steam,edible oil microemulsion,and methylene blue solution,coated ACs showed excellent selective adsorption performance on different organics.The adsorbed ethanol can be self-desorbed in dry environment,and the organics can be desorbed after heat treatment at high temperature,possessing great regeneration performance.It has been proved that the surface structure of the modified AC presented a high aspect ratio（H/S）,facilitating the formation of condensation droplets from the top and side and maintaining a stable Cassie-Baxter state,with air pressure to resist the entry of water molecules.The critical diameter of the droplets bouncing on the surface was calculated to be 51.94μm,and the distribution rate of the droplets larger than 50μm was less than 4.5%.Therefore,the nucleating droplets possessed enough kinetic energy to bounce and prevented the surface from being wetted by water.（2）Based on the comprehensive analysis of actual grafting on surface groups and density generic function theoretical calculation,the grafting rate of propyl silane modified silica nanoparticles was 2.674 mmol·g^-1,and the total adsorption energy of water molecules on its surface was 0.251 e V·mmol·g^-1,demonstrating that propyl grafted nanoparticles have the weakest affinity to water molecules and the best moisture resistance in all schemes.For the highest ratio of total adsorption energy on the modified nanoparticles to toluene and water molecules,they could preferentially adsorb organics in the water vapor environment.Thus,the optimal modification scheme was determined,and the fluorine-free superhydrophobic nanoparticle solution was successfully prepared.Optimizing the coating process of nanoparticles on AC,the surface was pre-roughened,and then the functional nanoparticles were loaded on the surface of pretreated AC by rotary evaporation process.The obtained superhydrophobic ACs showed great moisture-proof stability at 180 days of high humidity and water immersion stability for 60 days.The modified AC retained excellent adsorption capacity for different organic solvents,presenting significant selective adsorption on a variety of volatile organic chemicals in high humidity environment,and efficient removal performance for chemical oxygen demand of different organic solution.And after the adsorption tests,the coated AC can be regenerated through vacuum drying,recovering the related adsorption performance indicators.（3）Based on the modification process on silica nanoparticles with high fluorinated grafting and crosslinking,the superamphiphobic coating with great oil immersion resistance for range hood application has been successfully developed.The obtained superamphiphobic coating with densified nano-porous structure,with the average nanopores spacing of 111±10nm,calculating the puncture pressure of 0.26 MPa according to the theoretical model.The wetting pressure of organics on the surface was composed of dynamic impact pressure,static immersion pressure and oil hammer pressure,which were 0.46 k Pa,0.46 k Pa and 0.24 MPa,respectively.The puncture pressure was always greater than the sum of the wetting pressure,so that the liquid droplets could maintain a stable Cassie-Baxter state on the coating surface.Thus,the as-prepared coating produced enough impalement pressure resistance to penetration of organics,showed significant improvement on the stability compared with other types of functional coatings.During the process of immersion in the artificial mixture of organic solvents,the superamphiphobic coating was able to keep the surface clean for 200 days,without any droplet residue and surface peeling,presenting good adhesion to the substrate and proper mechanical stability.（4）Based on the design concept of phase separation of particle agglomerates,the modified silica powder aggregates were dispersed in the inorganic binder solution.Driven by the difference of surface tension,the nanoparticles were re-reunited in the process of film formation coating and generating abundant particle microcapsule structures in the interior.During the abrasion process,the particle capsules were supposed to release a large number of functional nanoparticles in the process of abrasion,maintaining excellent repellency to organics.And by means of chemical bonding,inorganic binder can enhance the cohesion of coating components and the adhesion between coating and substrate,successfully developing the wear resistant superamphiphobic coating with self-healing performances.According to the testing results,oil droplets can easily roll off the coating surface without any adhesion after500 Taber abrasion cycles with 250 g load.Based on the mathematical formula fitting calculation,the coating elastic model was a cubic function of the average diameter of particles capsule,proving that the mass ratio of binder to nanoparticles was higher,the more conducive to form larger particle capsules.Thus,the elastic modulus of the coating was higher,which could produce enough rebound strength to prevent the structure from being destroyed,presenting excellent nanomechanical properties and mechanical stability.