Water-based layer-by-layer surface chemical modification of biomimetic materials: oil repellency

Biomimetic materials possessing hierarchical surface roughness thrive when complementary terminal chemical functionality is introduced. However, incorporating terminal functionality on the biomimetic material is the challenge, especially, when its roughness needs to be preserved. Hence, we report surface chemical modification of biomimetic materials through water-based layer-by-layer deposition. The amine terminated biomimetic replica PDMS-replica(Silica/NH2) was prepared by treating silica-modified replica (i.e., PDMS-replica(Silica)) with the aqueous solution of branched ethoxylated polyethylenimine (EPEI). Next, -CF3 terminal PDMS-replica(Silica/NH2/CF3) was obtained by treating PDMS-replica(Silica/NH2) with the aqueous solution of phosphate ester fluorosurfactant. PDMS-replica(Silica/NH2/CF3) showed superhydrophobicity (advancing θwater ≈ 140°) and high oil repellency (advancing θoil ≈ 110°). X-ray photoelectron spectroscopy (XPS) revealed well-organized terminal -CF3 groups present on the PDMS-replica(Silica/NH2/CF3) surface. During the process of layer-by-layer deposition, the surface topography was monitored using scanning electron microscopy (SEM). This method could be extended to get desired terminal chemical functionality on the biomimetic materials which would furnish interesting surface properties in air or under water.