Synergistic effects of perfluoropolyether alcohol modification on the hydrophobicity and flexibility of waterborne nano-polyurea coatings

Abstract

Waterborne nano-polyurea coatings have attracted increasing attention as eco-friendly anti-corrosion materials, but their practical application is limited by insufficient hydrophobicity and flexibility. To overcome these limitations, a fluorinated grafted MDI, synthesized using 4,4′-methylenediphenyl diisocyanate (MDI) and monohydroxyl-terminated perfluoropolyether (PFPE-OH), was introduced into a waterborne nano-polyurea system. The modified coating was comprehensively evaluated through structural characterization, analysis of physical properties, and application performance testing. The effects of PFPE-OH content on the structure and performance of the coatings were systematically investigated. The FT-IR and 1H NMR results demonstrated successful incorporation of PFPE-OH into the polyurea network through the formation of urethane linkages, while 19F NMR confirmed the introduction of PFPE side chains. The fluorinated groups were uniformly dispersed in the modified coatings as revealed by SEM-EDS, and XPS results verified their enrichment at the coating surface, with the F atomic percentage reaching 38.92 at% for the modified sample (JM-4). With increasing PFPE-OH content, the water contact angle increased from 63.3° to 108.4°, the elongation at break first increased from 2.40% to 3.98% and then decreased to 0.69% at excessive PFPE-OH loadings, and the Shore hardness decreased from 61 to 42, indicating significant improvements in both hydrophobicity and flexibility. An appropriate PFPE-OH content also contributed to enhanced thermal stability, abrasion resistance, neutral salt spray resistance, and adhesion performance. In particular, when the MDI/PFPE-OH feed ratio was 1 : 0.08, the coating exhibited an adhesion strength of 5.33 MPa and superior overall performance. These findings demonstrate that PFPE-OH modification is an effective strategy for achieving simultaneous enhancement of hydrophobicity and flexibility in waterborne nano-polyurea coatings.