| Freezing and refrigeration play an essential role in the quality preservation of perishable food products,however,the undesired ice or frost accretion on freezing facility surfaces can result in significant energy consumption,along with a reduction in production efficiency.Recently,biomimetic surfaces with superwettability have been proven to delay icing and frosting on cold substrates or to de-ice and de-frost easily,with the potential of supplementing or even replacing conventional de-icing or defrosting technologies.The application of superwetting strategy to the food freezing and cold chain is of great significance to reduce the adverse impact of icing and deicing on economy and environment.However,how to design practical,scalable and food-safe bionic superwetting surfaces for applying in food processing facility and environment is an urgent problem to be solved.In this paper,a completely water-based silane modified hydrophobic nano-coating was prepared by a simple,low-cost,environmentally friendly and scalable method,and the effects of the amount of nanoparticles and modifier on the morphology and hydrophobicity of the coating were investigated.After that,the binary superhydrophobic nano-coating was synthesized by introducing dual-scale nanoparticles based on the formulation of silane nano-coating with the best hydrophobic effect,and the influence of mass ratio of dual-scale nanoparticles on the morphology characteristics,hydrophobicity and anti-icing properties of the coating was investigated.Finally,on the basis of organosilane and stearic acid modified hydrophobic nano-coatings,two kinds of food-safe slippery lubricant-infused porous surfaces were successfully prepared by injecting lubricating oil,and the frost resistance,fast defrosting characteristic and icephobicity of slippery lubricant-infused porous surfaces and superhydrophobic nano-coatings were comparatively studied.The specific conclusion are as follows:1.The amount of nano-filler and modifier can affect the morphology and surface free energy of silane modified nano-coatings,thus affecting the hydrophobicity of the coating surfaces.Thereinto,excessive Si O2 nanoparticles(NPs)and excessive HDTMS can make nano-coatings become relatively flat with decreasing roughness;the surface free energy of nano-coatings will be lowered with excessive Si O2 NPs or inadequate HDTMS,which will also weaken the surface hydrophobicity.In the case of 6 mg/L Si O2 NPs and 30 mmol/L HDTMS,the prepared silane nano-coatings exhibits the best hydrophobic property(CA=153.1±0.1°,RA=7.3±1.2°),and this coating still remain high contact angle(CA=150.9±0.9°)and excellent water repellency after 40 sandpaper abrasion cycles,possessing good mechanical stability.2.The mass ratio of dual-sized nanoparticles used to prepare binary superhydrophobic coatings played an important role in determining the surface roughness and wettability.And the introduction of appropriate proportion of dual-sized particles could increase surface roughness and thus contribute to improving hydrophobicity.When the particles mass ratio of 15 nm and50 nm was 1:1,the coating exhibited the best hydrophobicity,the CA was as high as158.8±0.4°and the RA was as low as 4.3±0.58°.Combined with the results of SEM and 3D morphology test,the use of dual-sized nanoparticles was more conducive to the construction of micro-nano composite rough structure,forming more air pockets,and the contact angle increases with the surface roughness,which conformed to the relationship between solid-liquid area fraction and contact angle described in Cassie-Baxter equation.3.The superhydrophobic surface could effectively delay the droplet icing,and the freezing delay time increases with the increase of hydrophobicity of the coating.At-10?,the freezing delay time of 30water droplet on HN0-1,HN5-1,HN1-2,HN1-0,HN2-1 and HN1-1 was respectively 155.18 s,237.24 s,318.27 s,417.22 s,472.05 s and 1171.18 s.Combined with the theoretical values of the solid-liquid interface contact area fraction calculated by the Cassie-Baxter equation,reveals the relationship among surface roughness,hydrophobicity and icing delay:The rougher the surface was,the stronger the hydrophobicity was,the smaller the total area of three-phase contact interface and the fraction of solid-liquid contact area were,the slower the heat transfer rate of the droplet to the substrate was,and the longer the icing delay time was.4.The binary superhydrophobic nano-coating exhibited some anti-icing durability under low temperature and repeated freeze-thaw conditions.Under the conditions of-12?,-14?,-16?,-18?and-20?,the freezing delay time of HN1-1 was 628.84 s,504.97 s,444.37 s,77.71 s and 65.08 s,respectively,indicating that the icing-delay performance of HN1-1basically failed when the cold plate temperature was about-20?.After 30 freeze-thaw cycles,the freezing delay time of HN1-1 at-10?was reduced from 1171.18 s to 253.54 s.5.A novel anti-icing material obtained by impregnating hydrophobic porous coatings with food-safe lubricating oil was prepared,and it was confirmed that both the silane/stearic acid modified hydrophobic nano-coatings and the corresponding slippery oil-infused surface exhibited excellent frost resistance and defrosting performance.The results of anti-frosting test showed that the hydrophobic modified nano-coatings and the slippery lubricant-infused porous surfaces mainly induced frost nucleation in“random point nucleation”and“edge nucleation”mode,which could significantly inhibit the formation and propagation of frost.Compared with the control,both of the two surfaces could delay frosting and significantly reduce frost accumulation(p<0.05),additionally,the accumulated frost and melted water on those nonwetted sufaces could be easily removed under gravity.6.The slippery lubricant-infused porous surface showed much lower ice adhesion strength than the hydrophobic modified nano-coatings,and exhibited basically icephobic durability.While the(super)hydrophobic nanocoatings didn't show icephobicity,deicing required shear force was even greater than that on bare aluminum.The ice adhesion strength of SHN1-1 and TSN1-1 in the deicing experiment was only 5.7±3.7 k Pa and 12.47±4.7 k Pa,the shear strength required to separate frozen pork and potato from slippery lubricant-infused porous surface was one order of magnitude lower than that of the control group,indicating that the ice performance of the smooth surface was better than the textured surface.In addition,the inexpensive and safe edible oil could be a potential candidate for lubricating fluid of anti-icing slippery porous materials.After 10 cycles of deicing,both the ice adhesion strength of SHN1-1 and TSN1-1 increased,but was still lower than 1/2 of that of the control group. |
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