Investigation On Anti-scale Characteristics And Mechanism Of Polydopamine Coating On Metal Surface

CaCO₃scale deposited on the surface of heat exchange equipment can increase the surface thermal resistance and fluid flow resistance,leading to reduced heat transfer efficiency and a series of safety and economic issues.The surface modification can isolate the metal base from the outside environment,reduce the adhesion strength between the scale and the heat transfer interface,and decrease scale deposition.Polydopamine,a biomimetic material,is widely used in the preparation of complex scale inhibition coatings because of its strong binding ability,good flexibility,excellent stability,and corrosion resistance.Polydopamine plays a major role in adhesion and fixation,but it is unclear whether it has a scale inhibition effect.In this study,experimental and molecular dynamics simulation methods were employed to investigate the anti-scale characteristics and mechanisms of polydopamine coatings.This study proposes an efficient one-step electrodeposition method to prepare polydopamine coatings in a few minutes with high stability and uniformity on Q235 carbon steel,which is prone to scaling and has poor corrosion resistance.The coating was characterized and analyzed by FIB-SEM and EDS et al.The tape peeling text showed that after200 times of sticking and peeling,the water contact angle of the surface changed by only 3.6%.And the electrochemical corrosion testing showed that the polydopamine coating had a corrosion inhibition efficiency of 88.56%for Q235 carbon steel.The above results indicated that the polydopamine coating had excellent stability and corrosion resistance.The immersion of carbon steel and the polydopamine coating in oversaturated Ca CO₃solutions at 50℃,70℃,and 90℃for 12 h showed that the Ca CO₃deposition on the coating surface was less than that on the carbon steel surface.The corresponding scale inhibition rates were 47.37%,55.02%,and66.96%,respectively.Furthermore,the polydopamine coating showed better scale inhibition performance at higher temperatures.Based on the molecular dynamics simulation method,the mechanism of inhibition of Ca CO₃adsorption by polydopamine coating was revealed from the microscopic level.The simulation results revealed that compared to the iron plate model,the polydopamine coating model significantly reduced the adsorption probability of Ca CO₃.In the iron plate model,the interaction energy between the dense water adsorption layer on the plate and Ca CO₃at 343 K was-61.65 e V,indicating a strong interaction force.The introduction of polydopamine coating increased the distance between the wall atoms and water molecules,weakening the van der Waals forces between the wall iron atoms and water molecules near the wall surface,resulting in the inability to form a dense water adsorption layer near the wall,and thereby reducing the adsorption of Ca CO₃on the wall surface,in agreement with macroscopic experimental observations.In addition,the adsorption difference of Ca CO₃between the iron plate model and the polydopamine coating model at different temperatures was analyzed.The results show that,with the increase of system temperature at 323 K,343 K and 363 K,the thermal motion of ions intensifies,and it is easier to form Ca CO₃clusters.In the iron plate model,Ca CO₃clusters tend to be adsorbed near the wall,and the adsorption rate increases with the increase of temperature.However,in the polydopamine model,calcium ions and carbonate ions are more likely to combine in solution to form Ca CO₃clusters,resulting in lower diffusion degree and further reducing the probability of collision with the wall.