(604g) Robust Polymer Coatings for Controlling CaCO3 Heterogeneous Nucleation in Thermal Desalination

Heterogeneous nucleation of CaCO₃ widely occurs during inorganic fouling in thermal desalination. The formation of CaCO₃ foulants results in increased heat transfer resistance, reduced flow rates, and thus impaired efficiency of desalination processes. Approaches for controlling CaCO₃ heterogeneous nucleation are therefore highly desired for energy-efficient and cost-effective solutions for fouling problems in thermal desalination. For industrial applications, any surface treatment must be stable under harsh operational conditions. Additionally, the surface modification layer needs sub-micron thickness to maintain good heat transfer. However, such robust nanoscale thin films for tuning heterogeneous nucleation of CaCO₃ have not yet been reported.

In this work, we developed a series of initiated chemical vapor deposited (iCVD) covalently crosslinked organic networks. These ultrathin (≤100 nm) coatings have low surface energy and small work of adhesion with CaCO₃. Consequently, the energy barrier for CaCO₃ to nucleate on these iCVD polymer surfaces was found over 90% of the Gibbs free energy for CaCO₃ homogeneous nucleation. These results lead to slow nucleation kinetics with extended induction periods. We also investigated the nucleation and growth of CaCO₃ on untreated and iCVD-coated Cu/Ni foils in hot synthetic sea water similar to the operational conditions in multistage flash (MSF). We found that surface electrochemical oxidation of Cu/Ni during exposure to aqueous electrolyte at elevated temperatures significantly enhances the heterogeneous nucleation of CaCO₃. Our iCVD polymer coatings provide excellent passivation for Cu/Ni with corrosion rates as low as 6.8x10^-5mm/yr, therefore effectively inhibiting corrosion-induced heterogeneous nucleation of CaCO₃. In addition, our iCVD coatings exhibit good stability for long-term exposure to boiling synthetic sea water. The iCVD thin films presented here are promising for inorganic fouling control in thermal desalination processes.