Fluorine-Free Hydrophobic Polymer Brushes for Self-Healing Coatings

Fluorinated hydrocarbons are excellent building blocks for hydrophobic coatings but also yield undesirable toxicity and environmental persistence. In precision industries such as high-resolution printing, polymer brushes are a valuable tool, as they can be tuned on the nanometer scale and can impart the underlying surface with desired properties and/or functionalities. Here, we report that the beneficial properties typically associated with (partially) fluorinated polymer brush coatings can to a large degree also be achieved with their nonfluorinated counterparts. To this end, we have successfully grafted 13 poly(alkyl methacrylate) homopolymer brushes from a flat silicon surface using surface-initiated atom transfer radical polymerization (SI-ATRP). These polymer brushes were characterized by XPS, ellipsometry, and static water contact angle measurements. They were then shown to be repeatedly self-repairing by thermal treatment at 120 °C after damage by pH 3, with longer side chains being more resistant to damage from the acid. Branching of the side chains did not significantly influence this resistance, but it lowered the static water contact angle. Some polymer brushes with intermediate side chain length displayed an increase in the contact angle over the first four cycles. This was not caused by impurities but was the result of an annealing effect that improved the packing of the side chains of the brushes. In all, these coatings are suitable, self-healing, environmentally friendly, and fully nonfluorinated alternatives for current fluorine-based hydrophobic coatings.