Design And Protective Properties Of Lubricant Infused Surface Based On Nano/Micro Porous Aluminum Substrates

Creating bionic coatings with excellent protection by mimicking the surface morphology and chemistry of plants and animals has received much attention in recent years.Inspired by Nepenthaceae,micro-or nanoporous substrates have been used to lock low-surface-energy lubricating liquids to form liquid-solid composite surfaces,which were defined as lubricant-infused surfaces(LIS).These liquid-solid composite surfaces exhibit superior water-repelling,attachment inhibiting,and self-healing abilities,and wildly used in anticorrosion,anti-icing,and anti-microbial.However,in the practical application,the LIS has to face the challenge of the lost of lubricant,which may cause by the defects during the fabrication processes,the liquid nature of infused lubricant,and especially the harsh environment.The failure LIS would corrode by external fluid attached by a microorganism or covered by ice,and finally arouses lots of safety problems.Because of these issues,we prepared a series of materials including liquid oil,colloid,gels mixed with oil,and solid/liquid switchable materials,to fabricate the LIS with a long lifetime and excellent protection function.Their protection mechanism including self-healing,replenishment,and self-secretion was studied.The main results are shown below:(1)The durable LIS was fabricated by infusing the lubricant into anodized aluminum oxide(AAO)layer with thickness of 50μm through the vacuum immersion method.This lubricant infused deep nanochannel(LIDN)exhibit a more stable mechanical property and durable anticorrosion performance because of its thick nanoporous substrate and abundant lubricant stored in the pores.The cryogenic scanning electron microscope(Cryo-SEM)observation provided insights into the self-healing process.The Potentiodynamic Polarization curve(PDP)results demonstrated the self-healing ability of LIDN whose corrosion current density barely changed and remained at 2.99×10-10 A·cm-2 even after being cracked.The Electrochemical Impedance Spectrum(EIS)tests showed that the impedance moduli in the low-frequency region(|Z|0.01Hz)remained stable at 4108Ω·cm2 for the LIDN immersed in NaCl solution for 85 days.Under tribological conditions,the low friction coefficient(0.12),the low depth of wear track(4.5 μm)and the well-preserved surface morphology indicated the excellent mechanical durability of the LIDN.The deterioration process of the LIDN was investigated under long-term immersion in 1 M NaCl solution for over 210 days.The failure process of the LIDN was observed by The Cryo-SEM and quantitatively studied by EIS.Firstly,the smooth surface lubricant layer gradually dissolved at a relatively constant rate until the porous AAO substrate got exposed.Then the lubricant stored in the nanochannels continuously dissolved untile the barrier layer was attacked.(2)Based on the study of liquid lubricant infused surface,solid Fe3O4 nanoparticles were mixed with lubricant to infuse into AAO for the fabrication of the ferrofluid infused surface(FIS).The FIS has special dynamic protection performance and prolonged durability through its particular replenishment property.Applied with a magnetic field,the ferrofluid reconfigured on the surface to repel water condensation and shed off pinned droplets.Additionally,the durability of FIPS was highly strengthened by using the magnetic field to maintain the ferrofluid in the substrate for longer time or replenish the empty nanochannel by driving the ferrofluid from the outside environment.The EIS tests showed that the impedance-frequency curves in Bode plot almost overlapped duiring the 80 days’ immersion in NaCl solution,which indicate more durability of FIS under magnet filed.The replenishment of the deteriorated FIPs was confirmed by Cryo-SEM that showing the refilling of the empty nanochannel.The remaining ferrofluid in the failed nanochannels could also be re-assembled at the surface to prevent the adhesion of bacteria.(3)The lubricating-gel that made by synthesizing the polydimethylsiloxane(PDMS)with silicon oil and Fe3O4 nanoparticles was used to infill the porous aluminum substrate for enhanced durability and self-secretion property.The magnetic lubricating-gel filled surface(MLFS)was characterized as a multi-porous structure and special distribution of the pores with big size and small size.These structures enable the MLFS a balance in the abundant oil capacity and minimum oil lost.The gel would vibrate under a magnetic field that makes the oil pores being compressed and secreting oil to cover the deteriorated surface.The regained slippery surface and the physic impact of the vibrated gel could highly improve the anti-icing property.The ice adhesion decreased from 37.8 kPa to 4.1 kPa and the nucleation could also be removed.(4)To enhance the LIS with strong durability,a solid-liquid switchable LIS was developed by infusing low-melting cocoa oil and Fe3O4 nanoparticles into porous AAO substrate,which we called nanoparticles&lubricant infused surface(NP-LIS).Attributing to the high photothermal effect of Fe3O4 nanoparticles which absorb the energy of IR irradiation,the solid lubricant under environment temperature of-10℃ was heated to a saturation surface temperature of-45℃,melting into a smooth liquid surface with high hydrophobicity and slippery performance(water contact angle of 122° and sliding angle of-5°).The enhanced defrosting performance and low ice adhesion strength(0.3 kPa)were attributed to the combination of the generated heat and slippery property of a melted lubricant.Additionally,the NP-LIS possessed high mechanical durability due to the self-healing effect of the lubricant in the liquid state and the high stability of the lubricant in the solid-state.The damaged surface and deteriorated wettability could be recovered after repeated abrasion test due to the melted lubricant that flowed into the cracked and reformed a smooth surface.The solid lubricant could withstand the sliding of thawed frost/ice and long-term impact of flowing water,remaining the water contact angle and sliding angle steady.This switchable surface may provide new insights into the design and development of the next generation of anti-icing coatings.In summary,the durability of LIS could be improved by developing a robust microstructure of the substrate or improving the liquid lubricant into a complex solid-liquid system.The environment responsive nanomaterials are an excellent strategy to enhance protection performance by repairing the deteriorated surface.The environment responsive LIS may contribute to the design of a durable surface and promote its practical application.