Preparation Of Modified Organopolysilazane And Its Application In The Construction Of Stable Hydrophobic Coatings

In the construction of hydrophobic surfaces or coatings,a common problem is that low-surface-energy materials used as surface modifiers have weak interaction with the substrate,so that the stability and durability of the prepared surface or coating cannot meet the requirements of practical applications.To solve this common problem,we put forward a new strategy for constructing a stable hydrophobic coating based on the excellent anchoring effect of organopolysilazane(OPSZ)that can be used as an anchor molecule.In this work,differen modified OPSZs with excellent anchoring effect and hydrophobicity were designed and synthesized via the chemical modification of OPSZ;and several series of hydrophobic coatings were constructed on a substrate surface using the prepared modified OPSZ as a main coating material.The chemical composition,microstructure morphology,wettability,and physicomechanical properties of the surfaces of the constructed coatings were characterized and analyzed by using modern testing techniques;and their easy-cleaning properties,durability,and so forth were also investigated.Based on the comparative analyses of the experimental results,the relationship between composition-structure-performance of the constructed coatings was established.The main contents and results of this study are as follows.(1)Four long-chain alkyl compounds,CA-HDI,DA-HDI,OA-HDI and MA-HDI,were synthesized by the condensation reaction of 1-hexadecanol(CA),1-dodecanol(DA),1-octanol(OA)and methanol(MA)with hexamethylene diisocyanate(HDI),respectively.And three types of modified OPSZs with different hydrophobic chains were successfully synthesized under suitable reaction conditions using perfluoropolyether methanol(PFPE),vinyl MQ silicone resin(MQ),synthesized long-chain alkyl compounds and ethyl isocyanate(EI)as a modifier,respectively.They are denoted as OPSZ-PFPE,OPSZ-MQ,an alkyl compound-modified OPSZ and OPSZ-EI as its control,respectively.The as-prepared modified OPSZs,as well as the unmodified OPSZ,were used separately as a coating material;and the corresponding modified OPSZ coatings and a control coating OPSZ@Glass were constructed on the surface of a glass slide as a substrate.Besides,the modified OPSZ/inorganiccompositecoatingswithdifferentcompositions,OPSZ-PFPE-5@DE/SiO₂@Glass,OPSZ-DA-HDI-3@DE/SiO₂@Glass,and OPSZ-MQ-5@CDC@Glass,were also constructed on the substrate surface by using various inorganic substances as additives,including diatomite(DE MPs),SiO₂nanoparticles(SiO₂NPs),soot(CS)and carbon nanotubes(CNTs).(2)The constructed modified OPSZ coatings and the modified OPSZ/inorganic composite coatings have strong adhesion to the substrate,which can reach level 0.The modified OPSZ coatings exhibit a high hardness close to that of the control coating OPSZ@Glass and almost the same light transmittance as OPSZ@Glass.Among them,the OPSZ-PFPE coatings possess the highest surface hardness,3 H or 4 H;and show good solvent-wiping resistance,heat resistance and thermal stability.(3)The constructed OPSZ-PFPE coatings,OPSZ-MQ coatings and alkyl compound-modified OPSZ coatings present a water contact angle(WCA)in a range of 107.6°?110.7°,106.7°?109.5°and 93.1°?110.4°,respectively,reaching the hydrophobic regime and higher than the WCA(92.7°)of the surface of the control coating OPSZ@Glass.And with an increase in the content of PFPE or MQ in the modified OPSZ,or with an extension of its alkyl side-chain length,the constructed modified OPSZ coating can exhibit a higher WCA.The constructed modified OPSZ/inorganic composite coatings possess a rough surface with hierarchical micro-/nano-structures,and show a much higher WCA than the corresponding modified OPSZ coatings,approaching or or achieving the superhydrophobic regime.For the composite coatings containing a constant amount of DE/SiO₂,OPSZ-PFPE-5@DE/SiO₂@Glass and OPSZ-DA-HDI-3@DE/SiO₂@Glass,the WCA varies in the range of 152.8°?161.8°and 151.4°?159.8°,respectively,and the sliding angle SA in the range of 2.5°?8.7°and 3.4°?9.4°,respectively.For the composite coating OPSZ-MQ-5@CDC@Glass with a constant mass ratio of inorganic CS/DE/CNTs(CDC),the WCA and SA lie in the range of146.9°?158.6°and 4.2°?8.3°,respectively.As the content of SiO₂or CS/DE/CNTs in these composite coatings increases,the WCA and SA on the surface of the coatings show increasing and decreasing trends,respectively.(4)The easy-cleaning properties of the surfaces of the constructed coatings were investigated and evaluated via the scratch-wipe test and the contaminant removal test.The results indicate that compared with the coating OPSZ@Glass and pristine glass as a control,the modified OPSZ coatings and the modified OPSZ/inorganic composite coatings have excellent easy-cleaning properties.(5)The mechanical robustness,chemical resistance and ultraviolet(UV)aging resistance of the surfaces of the modified OPSZ/inorganic composite coatings were evaluated through a sandpaper abrasion test,acid/base immersion tests and UV(313 nm)radiation,respectively.The studies show that after being abraded for 15 cycles or immersed in different acid and alkali solutions for 24 hours,the composite coating OPSZ-DA-HDI-3@DE/SiO₂-5@Glass can still maintain high hydrophobicity with WCA around 146.1°or superhydrophobicity with WCA above 155°,respectively,so exhibiting good stability to external forces and chemicals.Moreover,the WCA of OPSZ-MQ coatings only decreases by 0.4°?1.4°after being exposed to UV radiation for 24 hours,thereby showing a good ultraviolet aging resistance.(6)The composite coating OPSZ-MQ-5@CDC-4@Glass containing photothermal material CNTs will heat up significantly after exposure to sunlight for 30 s and 180 s,whose surface temperature can rise from 26.6°C to 40.5°C and 55.4°C,respectively;and under sunlight,the melting time of an ice cube placed on the composite coating is only 10 minutes,which is 4 to 5 minutes shorter than that on the pritine glass used as a control.This proves that CNTs can endow the coating with photothermal performance and photothermally induced ice-melting performance to a certain extent.The above work undoubtedly opens up a new avenue to solve the common problems in the construction of a hydrophobic coating or surface;and the obtained results can lay a solid theoretical and practical foundation for the multifunctionalization of OPSZ and its application in the construction of durable functional coatings.