(368a) Development of Advanced Coatings with Special Wettability for Different Applications

Research Interests: surface wettability, coatings, thin film deposition, 3D printing, membrane-based separation.

Abstract

Special wettability has attracted significant attention in scientific research and industrial technology in past decades. For example, simultaneously hydrophilic/oleophobic surfaces are desirable in many applications such as oil-water separation, anti-fogging, self-cleaning, etc. However, achieving such surface wettability is challenging because of the higher surface tension of water than oil, leading to the fact that water has a greater wetting contact angle than oil on most solid surfaces. Here, we firstly established an approach to fabricate oil-water separation membranes by in-situ polymerization of a zwitterionic hydrogel on 3D-printed membranes. The contact angle tests and ATR-FTIR show that such membranes readily adsorb water and becomes simultaneously hydrophilic/oleophobic. The oil-water separation tests indicate that the water-adsorbed membrane is highly efficient in gravity- and capillary force-driven separation in 31 cycles. Secondly, we provided a simple and effective method of making plastic surfaces hydrophilic/oleophobic. Poly (methyl methacrylate) (PMMA), polystyrene (PS), and polycarbonate (PC) have been coated with a perfluoropolyether (PFPE) (i.e., commercially known as Zdol) via dip coating and then irradiated with UV/Ozone. The contact angle tests indicate that the treated plastics are simultaneously hydrophilic/oleophobic, which is stable in an aging period of 4 weeks. Furthermore, they exhibit superior anti-fogging performance and detergent-free cleaning capability compared to untreated plastics. These two works demonstrate the potential of simultaneously hydrophilic/oleophobic surfaces in many important applications.

The second part of my PhD research focuses on the development of hydrophobic coatings on an oral sorbent material with high capacity for NH₄⁺, which can lower blood urea level and mitigate the dialysis burden for end-stage kidney disease (ESKD) patients. Zirconium phosphate (ZrP) is an amorphous cation ion exchanger with high NH₄⁺ binding capacity as a sorbent material, but its selectivity to remove NH₄⁺ is limited in presence of other competing ions in water solution. Previous works have developed a gas-permeable and hydrophobic perfluorocarbon coating on ZrP, which improves ZrP’s NH₄⁺ selectivity. However, the coating preparation procedure, a wet chemistry approach, is lengthy and time-consuming, and more importantly, the large amount of usage of acetone poses a concern for the application of ZrP as an oral sorbent. Thus, we here developed a solventless coating protocol that effectively coats ZrP with Tetraethyl orthosilicate (TEOS) and 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (FOTS) via thermal vapor deposition (TVD). X-ray photoelectron spectroscopy (XPS) and contact angle measurements verify the two coating precursors are successfully deposited on ZrP surface, and the coating condition was optimized by the results of in vitro static binding study. The dynamic binding study of competing ions on Na-loaded ZrP with TVD coatings yields a maximum NH₄⁺ removal (~3.2 mEq/g), which can be improved to ~4.7 mEq/g if H-loaded ZrP under the same coating condition is used in basic stock solutions. More importantly, both materials barely remove Ca²⁺ and show excellent acid resistance. The significant improvement in NH₄⁺ binding capacity and selectivity reported here establishes a highly promising surface modification approach to optimize oral sorbents for ESKD patients.