Spontaneous, phase-separation induced surface roughness: A new method to design parahydrophobic polymer coatings with rose petal-like morphology
Résumé
While the development of polymer coatings with controlled surface topography is a growing research topic, a fabrication method that does not rely on lengthy processing times, bulk solvent solution, or secondary functionalization has yet to be identified. This study presents a facile, rapid, in situ method to develop parahydrophobic coatings 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 phase separation causes differences in composition and cross-link density within the network, which leads to local variations in polymerization shrinkage across the non-constrained material interface. Domains with higher cross-link densities shrink and contract towards the bulk material more dramatically, permitting the formation of rough surfaces with sub-micron sized spheres enriched in PVDF 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.