Preparation And Properties Of Sepiolite-based Multifunctional Super-wetting Composite Coating

Inspired by super-wetting phenomenon of nature,super-wetting surfaces have received much attention after being discovered.Their unique wetting properties have broad development prospects in daily life and industrial production fields,such as waterproof fabric,building of self-cleaning surface,fluid transportation,oil-water separation,etc.So far,many researchers have prepared a variety of materials with super-wetting properties,such as superhydrophobic,superhydrophilic,superoleophobic,superoleophilic,superhydrophilic/underwater superoleo-phobic,etc.However,the current super-wetting materials generally have disadvantages of expensive raw materials,complicated preparation process and poor mechanical stability.Sepiolite,as a natural clay mineral,has many characteristics of low-cost,large surface area,and rich hydroxyl groups on surface,which can be used to prepare super-wetting functional materials.However,there is relatively little research on sepiolite in the field of super-wetting functional materials.Therefore,in this paper,low-cost sepiolite is taken as the research object.After being modified,through spray-coating method,superhydrophobic,superamphiphobic,super-hydrophilic,superoleophobic and other sepiolite-based multi-functional super-wetting composite coatings with good chemical and mechanical stability are constructed.The surface chemical composition and microstructure changes of the modified sepiolite and the self-cleaning and anti-corrosion properties of the corresponding composite coating are systematically studied,and the related microscopic mechanism is also clarified.Details as follows:(1)The sepiolite surface is modified with polysiloxane(POS)formed by the hydrolysis and condensation of hexadecyltrimethoxysilane(HDTMS)and tetraethylorthosilicate(TEOS).The modified sepiolite(Sepiolite@POS)and epoxy resin(EP)are used as the main raw materials to prepare Sepiolite@POS/EP superhydrophobic composite coating by spraying.The results show that sepiolite modified with POS has good superhydrophobic properties.When the mass ratio of Sepiolite@POS to EP is 7:5,the corresponding coating exhibits excellent superhydrophobicity,good chemical stability,mechanical stability,and self-cleaning performance.The contact angle(CA)of the coating is greater than 160°,and the sliding angle(SA)is less than 5°.This is mainly because that Sepiolite@POS endow the coating with low surface energy and micro-nano rough surface structure constructed by spray coating.The superhydrophobic coating can be successfully constructed on the surface of substrates such as wood blocks,steel sheets,A4 paper,etc.In addition,the melamine sponge is immersed in the mixture of Sepiolite@POS and EP,which gives the melamine sponge superhydrophobic and superoleophilic properties.The modified melamine sponge can quickly remove oil in water.The study confirms that the Sepiolite@POS/EP composite coating with good superhydrophobicity not only can be used to protect a variety of substrate materials and keep surface clean,but also it can be used in oil-water separation and other fields.(2)Sepiolite is dyed by adsorbing rhodamine B(RB).Then,the dyed sepiolite(SEP-RB)is modified with hexadecyltriethoxysilane(HDTES)and TEOS to obtain superhydrophobic dyed sepiolite(SEP-RB@POS).SEP-RB@POS and EP are mixed in proportion to prepare the dyed and superhydrophobic SEP-RB@POS/EP with composite coating by spraying.The research shows that the dyed coating has outstanding superhydrophobicity and self-cleaning ability.This shows that the superhydrophobic modification protects the composite coating well,which can greatly reduce the discoloration of the coating due to acid and alkali corrosion,thereby increasing the service life of the color coating.At the same time,the composite coating still maintains good superhydrophobicity after 50 times of adhesive tape test,which shows that the coating has good mechanical stability.(3)Modified sepiolite(SEP@FPOS)is obtained by using perfluorooctyl trichlorosilane(PFOTS)and TEOS to hydrolyze and condense to form fluorinated polysiloxane(FPOS)grafted on the surface of sepiolite,and mixed with EP to prepare superamphiphobic SEP@FPOS/EP with composite coating by spraying.Studies show that the composite coating is very repellent to water and oil.Even sunflower oil with a surface energy of only 27 mN·m~-11 exhibits a contact angle of 152.8°on the coating surface.The composite coating can still maintain good superamphiphobicity in harsh environments such as acid/alkali solution,long-term ultraviolet light and low temperature.At the same time,the composite coating can withstand 100 g of falling sand impact,which shows good mechanical stability.(4)The reaction of poly(diallyldimethylammonium chloride)(PDDA)and sodium perfluorooctanoate(SPFO)is used to modify sepiolite to prepare SEP@PDDA-PFO.PDDA-PFO provides SEP@PDDA-PFO with hydrophilic groups and oleophobic groups,so that the formed SEP@PDDA-PFO/EP with composite coating has good superhydrophilicity and superoleophobicity.The CA of water on the coating surface is less than 5°,while its CA of oil is greater than 150°.At the same time,the composite coating has good mechanical stability and will not be damaged by friction after being wetted by water.This is because that EP with high adhesion forms a solid skeleton during curing process of the coating,which improves the adhesion between the coating and the substrate,and avoids the shedding of SEP@PDDA-PFO during the friction process.In addition,spraying SEP@PDDA-PFO/EP on the surface of the stainless steel mesh can give the mesh superhydrophilicity and superoleophobicity,which can successfully achieve oil-water separation.This study effectively solves the problem that traditional lipophilic hydrophobic separation materials are easily polluted and difficult to recycle.