A critical design factor in the development of polymer coatings is the interaction between the synthetic material and the external environment. Specifically, the interfacial behavior with water is extremely important for coatings used in membranes, separations processes, microfluidic devices, and biomaterials applications. Nature provides many examples of surfaces that have unique interactions with water such as the self cleaning effect on lotus leaves, the ability of geckos to walk on water, or the strong water adhesion observed on rose petals. Closer study of these natural surfaces has identified that both low surface energy materials and rough interfaces are needed to design materials with unique wetting behavior. To design such surfaces synthetically, research on the design and fabrication of polymer coatings with controlled surface topography has been a growing research topic. However, few fabrication methods that do not rely on lengthy processing times, bulk solvent solution, or secondary functionalization have been identified towards this aim. This work presents a facile, rapid, in situ method to develop coatings with unique wetting behavior based on phase separation during photopolymerization. A comonomer resin of ethylene glycol diacrylate (EGDA) and 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) is modified with a thermoplastic additive (PVDF) to induce phase separation during polymerization. If applied to a glass substrate and photopolymerized, the EGDA:PFDA copolymer forms a homogeneous network with a single glass transition temperature (Tg) and slight hydrophobicity (θw ~ 114°). When the resin is modified with PVDF, phase separation occurs during photopolymerization producing a heterogeneous network with two Tg’s. The resulting Tg’s of the network indicate a phase rich in EGDA:PFDA copolymer, and a phase enriched in PVDF. The heterogeneous structure causes non-uniform shrinkage development across the material, as the copolymer-rich domains experience more significant volumetric shrinkage due to the higher concentration of acrylate functionalities than the PVDF-enriched areas. As phase separation proceeds via Nucleation & Growth, this yields a rough surface with PVDF-rich, sub-micron spheres dispersed in a continuous matrix of EGDA:PFDA copolymer. Both the surface roughness and hydrophobic components in the resin render these surfaces parahydrophobic with θw ~ 150°, high water adhesion, and a similar morphology to rose petals observed in nature.

Utilizing heterogeneous network formation to tune surface roughness: A method to control coating wettability

251st National Meeting (2016)

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