Preparation And Properties Of Geopolymer-based Silicone Nanofilaments Superhydrophobic Composite Coatings

For years,the development of inexpensive,environmentally-friendly,easily applicable and durability of the superhydrophobic coatings has always been the core problem in the application of superhydrophobic coatings in scientific and industrial application.As a new inorganic adhesives,geopolymer has a wide range of raw materials,simple preparation process,cost-effective and environmental friendly,and has shown many excellent properties in the field of coating application:strong bonding with walls,zero VOC emissions,high hardness,water and scratch resistance,no peeling,no cracking,no shedding,no mildew;at the same time,it also has fire resistance,acid resistance,marine corrosion resistance,and so on.The outstanding construction performance and artistic performance are presented.In this paper,a simple process for preparing water-borne superhydrophobic coatings by in-situ growth of silicone nanofilaments on the surface of geopolymer coatings is proposed for the first time.By brushing hydrogen-containing silicone oil on the surface of freshly cured alkaline cementitious materials and then curing in a sealed environment at 120'C for an hour,a composite coating with dense silicone nanofilaments on surface was obtained to achieve superhydrophobic modification of the original coating substrate.(1)The effects of modification temperature,method,time,moisture content in base material before modification,dosage of modified silicone oil,the molar ratio of H2O/Na2O in coating formulation and modulus of sodium silicate on the synthesis of silicone nanofilaments were investigated.The results showed that the key factors affecting the formation of silicone nanofilaments were sealing curing,modification temperature,modification time,moisture content of base material before modification and silicone oil dosage.The change of n(H2O)/n(Na2O),n(SiO2)/n(Na2O)in slurry formulation will not affect the smooth formation of fibers,only by affecting the surface morphology of the substrate and the moisture content of the system,and then the growth morphology of the fibers will be properly regulated.The most suitable modification method is as follows:once the base coatings which are cured at 60 ? have certain strength,can the modification process be carried out to ensure sufficient water content in the base materials to supply more 1D-SNFs formation.Subsequently,the coated wafer with a diameter of 40mm was coated with 0.05 g PMHS in a 120 ? oven and maintained in the sealed for 1 hour.Finally,the uniform and compact 1D-SNFs structure could be achieved on the surface of the geopolymer coatings.(2)Combining with the formation mechanism of NaA zeolite in situ transformed by geopolymers,it is confirmed that water plays an indispensable role in the in situ converted into NaA zeolite and the in situ synthesis of silicone nanofilaments.The main reasons for the successful growth of silicone nanofilaments on the surface of geopolymers are as follows:1)The surface of metal oxides can be completely hydroxylation after adsorbing a certain amount of water,and a large number of active hydroxyl groups can connect the hydrolyzed products of silane on the surface to form the nucleation sites of silicone nanofilaments.2)When cured in high temperature sealed environment,the surface of geopolymer can retain a certain thickness of film water layer for a long time,which provides a suitable growth environment for the hydrolysis and self-assembly of PMHS.3)The excessive alkali in the system can be used to catalyze the subsequent hydrolysis and self-assembly of silane and promote the formation of 1D-SNFs.(3)The structure,composition and properties of the superhydrophobic composite coating of metakaolin-based geopolymer-silicone nanofilaments show that the fibers are amorphous,mainly derived from the hydrolysis and self-crosslinking of PMHS,and are successfully grafted onto the geopolymer matrix.Laser scanning confocal microscopy(LSCM)and FESEM images show that micron and nano-scale roughness coexist on the surface of the coating.These characteristics enable the coating to retain the air layer when exposed to water,exhibit excellent self-cleaning performance when exposed to air,raise the contact angle to 167 degrees,and reduce the rolling angle to about 1 degrees.The surface wettability of the coating can be controlled by controlling the growth morphology of the fibers.(4)The performance test of superhydrophobic composite coatings shows that the coatings can maintain relatively stable self-cleaning and anti-fouling properties in air,and can withstand high temperature of 450 ?.They have good corrosion resistance to concentrated brine and strong oxidizing liquids,but their wear resistance and corrosion resistance to strong acid and strong alkaline liquids are poor.Fortunately,superhydrophobic properties can be restored through the repair and regeneration process.