Probing nanoscale chemical segregation and surface properties of antifouling hybrid xerogel films

Over the past decade there has been significant development in hybrid polymer coatings exhibiting tunable surface morphology, surface charge, and chemical segregation-all believed to be key properties in antifouling (AF) coating performance. While a large body of research exists on these materials, there have yet to be studies on all the aforementioned properties in a colocalized manner with nanoscale spatial resolution. Here, we report colocalized atomic force microscopy, scanning Kelvin probe microscopy, and confocal Raman microscopy on a model AF xerogel film composed of 1:9:9 (mol:mol:mol) 3-aminopropyltriethoxysilane (APTES), n-octyltriethoxysilane (C8), and tetraethoxysilane (TEOS) formed on Al₂O₃. This AF film is found to consist of three regions that are chemically and physically unique in 2D and 3D across multiple length scales: (i) a 1.5 μm thick base layer derived from all three precursors; (ii) 2-4 μm diameter mesa-like features that are enriched in free amine (from APTES), depleted in the other species and that extend 150-400 nm above the base layer; and (iii) 1-2 μm diameter subsurface inclusions within the base layer that are enriched in hydrogen-bonded amine (from APTES) and depleted in the other species.