Self replenishing polymeric coatings : repairing surface functionalities

Abstract

During the last decade, extensive research has been carried out on functional coatings with easy-to-clean/self-cleaning, anti-bacterial or anti-fouling properties, mainly driven by industrial demand but also by academic interest. Such properties are strongly related to the surface characteristics, in particular chemical composition and topography. Since damage of coatings can never be totally avoided, the introduction of self-replenishing mechanisms is one way to repair the surface properties and maintain a high performance of the coatings' functionality throughout an extended service life-time. Recently, we reported self-replenishing low surface energy (hydrophobic) polymer coatings which “self-repair” damaged surfaces by replenishing it with new low surface energy groups, e.g., fluorinated-dangling ends. These low surface energy dangling ends, covalently bonded to a cross-linked network, re-orient spontaneously from the bulk towards the new air-interfaces created by the damage. In our research, we pursued a dual experimental-simulation approach to understand in-depth this self-replenishing mechanism. First, we investigated the influence of different system parameters, such as the concentration of the low surface energy component and the molecular mobility span of the dangling ends, on the recovery of the coatings' hydrophobicity. The combined approach revealed the possibility of multiple healing events, the self-replenishing efficiency and the minimum “healing agent” concentration for a maximum recovery. Thereafter, we developed robust and easy processing self-replenishing superhydrophobic coatings. By incorporating inorganic nanoparticles in the polymer system, we designed surface-structured coatings which can spontaneously recover a low surface energy, partially responsible for the superhydrophobic behavior, at new structured surfaces created upon damage. The parallel simulations revealed the minimum thickness of the polymer layer for optimal self-replenishing ability and the distribution profile of the dangling ends at the various interfaces. The dual approach outlined above has been shown to be a fertile route to understand and design these complex materials and is expected to be applied in the future to other self-healing materials as well.