Fabrication Of Superhydrophobic Nano-ZnO/Epoxy Composite Coatings And Their Antifouling Performance Evaluation

Biofouling is a great challenge in the development of marine industry.For now,antifouling coatings are still used as the primary biofouling control strategies.Superhydrophobic nanocomposite coatings show great potential to replace toxic antifouling coatings due to their green antifouling performance.In this thesis,the nano-ZnO/epoxy composite coatings were prepared by an air spray coating method with epoxy resin as the main matrix and nano-ZnO as nano-filler.The effects of nano-ZnO content and particle size on the surface topography were studied.The correlations between surface roughness parameters,wettability,surface free energy,and antifouling performance were also investigated.A dynamic biofouling system was designed to evaluate the antifouling performance of superhydrophobic nano-ZnO/epoxy composite coatings under a series of low flow velocity conditions in the laboratory.The results could shed light on the future development of superhydrophobic nanocomposite coatings with antifouling performance.The main findings are as follows:（1）Fifteen nano-ZnO/epoxy composite coatings were fabricated with single-sized nano-ZnO（30 nm and 90 nm）and dual-sized nano-ZnO（weight ratios of 30 nm and90 nm nano-ZnO=1:1,1:5,and 1:9）.The results indicated that the coating topography can be controlled by using different sizes and concentrations of nano-ZnO.It showed great advantages in improving surface roughness to achieve superhydrophobicity of nanocomposite coatings by using dual-sized nano-ZnO.The 90 nm nano-ZnO agglomerated into bigger clusters,and consequently formed rougher surfaces with higher porosity.The smaller clusters agglomerated from 30 nm nano-ZnO partly filled the inter-cluster spaces,which was beneficial for improving the mechanical properties of nanocomposite coatings.The nano-ZnO/epoxy composite coatings fabricated by dual-sized nano-ZnO achieved a greater surface roughness with a lower nanoparticle concentration due to the combined effect of the“skeleton”and the“smaller clusters”.（2）The correlations of surface roughness parameters with wettability and antifouling performance were revealed.Three unique scenarios were proposed based on the relationship between the two key parameters:core void volume(V_vc)and core material volume(V_mc)to assess the relationship between surface roughness and solid-liquid contact area fraction.The V_vc and V_mc always presented positive correlations with surface roughness S_a.However,the V_vc/V_mc presented a positive correlation with S_a only in scenario 1(V_vc>V_mc).Due to higher air entrapment capacity and high abrasion resistance,superhydrophobic surfaces in scenario 1(V_vc>V_mc)exhibited better antifouling performance than the coatings in the other two scenarios.In the transitional state and Cassie state,the V_vc and peak sharpness dominate,respectively,consequently dominating the wettability and antifouling performance of nano-ZnO/epoxy composite coatings.（3）The effects of surface free energy on the wettability and antifouling performance of nano-ZnO/epoxy composite coatings were investigated.The solid surface free energy effect on WCA and CAH showed a positive correlation with solid-liquid contact area fraction.And the effect of solid surface free energy on CAH was greater than that on WCA.Due to the further reduced solid surface free energy,the super-hydrophobicity was achieved with a smaller nanoparticle concentration（40 wt%,Zn MF40-1:9）with an antifouling rate of 94.1%under static condition.（4）A laboratory evaluation method of antifouling performance under low flow velocity was studied.A parallel dynamic biofouling system for the evaluation of antifouling performance in the laboratory was set up.The flow velocity of this system could be accurately manipulated from 0 to 0.69 m/s.Then,this system was applied to study the impact of hydrodynamic shear force on adhesion morphology and biofilm conformation of Bacillus sp.The antifouling performance of superhydrophobic nano-ZnO/epoxy composite coatings under low flow velocity was also evaluated by using this dynamic biofouling system.It was found that the prepared superhydrophobic nano-ZnO/epoxy composite coatings exhibited great antifouling performance.Under the flow velocity of 0.10 m/s,the antifouling rate was up to 94.8%.And under the flow velocity of 0.31 m/s,the antifouling rate was still up to 91.1%.