Engineering Surface Hydrophilicity via Polymer Chain-End Segregation in Coatings Formed by Photopolymerization

The manipulation of surface chemistry, and more precisely the hydrophilic/hydrophobic nature of an interfacial material, is essential for many applications in coatings, biomaterials, and microfluidics. To engineer surface hydrophobicity, prior research has relied heavily on the segregation of low surface energy compounds, e.g., fluorinated alcohols or polymers, toward a free surface, thus increasing the surface hydrophobicity. While this approach is effective in creating hydrophobic interfaces, many applications in water harvesting and guidance require hydrophilic surface chemistries. Currently, many researchers utilize secondary postfunctionalization to integrate hydrophilic moieties at a surface, which typically requires additional precursors and reagents. Here, we demonstrate that the chain-end units of low-molecular-weight polystyrene additives can be exploited to promote segregation of hydrophilic moieties toward a free surface during network cure, thus increasing the wettability of polymeric surfaces in a single polymerization procedure. The efficacy of this approach depends on two factors: (1) the time available prior to vitrification and restriction of chain-end segregation and (2) the molecular weight of the polystyrene additive employed. We demonstrate that ambient photopolymerization provides a versatile, tailorable platform for manipulating the time available for chain-end segregation prior to vitrification. Our approach provides a framework from which hydrophilic surface chemistry can be easily engineered and patterned in rigid, cross-linked coatings without the use of secondary functionalization procedures.