Simulation‐Experimental Approach to Investigate the Role of Interfaces in Self‐Replenishing Composite Coatings

Abstract

which changes their surface characteristics and compromises their performance.One way to increase the durability of functional coatings is to create a system which is able to relocate the low surface energy groups at the damaged surfaces and recover the low surface energy properties, i.e., to introduce a self-healing function. In the case of surface-structured coatings, the repair of the surface roughness is an additional challenge. [ 5,6 ] One of the possible solutions reported by Li et al., [ 7 ] is the creation of a porous polymer coating with micro-and nano-scale structures, for which the 'healing agent' consists of a low surface energy component previously impregnated in the porous layer. After damage, this component migrates to the new porous coating surface restoring its (super)hydrophobicity when exposed to a humid environment. Another possibility is to encapsulate a surface-active material in nano-containers [ 8 ] which will be released at the surface upon damage. The self-organization of colloidal particles at interfaces has also been used to design materials with surface-healing properties by embedding colloidal silica particles in a perfl uorinated wax. [ 9,10 ] Upon damage and an annealing step (at 60 °C), the wax melts and the particles migrate to the surface, recreating a new topography covered by the waxy layer. [ 9 ] Recently, a surface-healing approach was reported by our group [ 11 ] which uses a polymer network that is able to replenish damaged surfaces with low surface energy components, autonomously and at room temperature. Perfl uoro-alkyl-terminated dangling chains connected to a poly(ester urethane) crosslinked network are able to spontaneously re-orient to new air interfaces created by damage. A polymeric spacer was included in the dangling chains in order to control their mobility and ensure surface reorientation, but also to provide the proper miscibility with the bulk network and avoid complete surface segregation. [ 11 ] This self-replenishing principle can be applied to recover surface properties such as hydrophobicity. However, for structured surfaces topography needs to be equally repaired or recreated. Hence we applied the self-replenishing principle on polymer layers with dual-scale roughness, [ 12 ] created by introducing inorganic nanoparticles with two different sizes (≈70/700 nm). For this system a multi-scale surface roughness is re-created by the damage, while the polymer layer between the particles serves as the source of low surface energy To investigate self-replenishing on surface-structured composite coatings a dual simulation-experimental approach is employed to study the decisive role of polymer-air and polymer-particle interfaces. Experimentally, the composite system consists of a cross-linked polymer network with fl uorinated-dangling chains, embedding colloidal SiO 2 nanoparticles which are incorporated in the network via covalent bonding. These particles provide the desired surface structure at the air-interface before and after damage. Any damage replicates the...

Self-replenishing ability of cross-linked low surface energy polymer films investigated by a complementary experimental-simulation approach

“…The extension of this efficient self-healing principle to complex systems, including structured surfaces on inorganic-organic composite materials will be reported in Ref. 42.…”

Self‐Healing Functional Surfaces

“…Role of polymer–particle interfaces on the distribution of low surface energy components in composite polymeric films: simulation profiles of the fluorinated “beads” per layer in a parallel direction to the particles surfaces in two situations: (spheres) non‐crosslinked and (stars) crosslinked to the polymer network—a) with high affinity to the particles surfaces and b) with no preference to particle surfaces or polymer “bulk.” Adapted with permission . Copyright 2014, Wiley‐VCH.…”

“…An example is given by the evaluation of the self‐replenishing of superhydrophobic surfaces with a simulation approach, applied on polymer films containing particles as roughness‐shaping elements . Two simulation setups were used to represent the air–polymer–particle interface and the particle–polymer–particle bulk ( Figure a–d).…”

“…Two main conclusions were drawn. Multiple self‐healing takes place but the SHE decreases until a certain critical thickness of the polymer film is reached after which no further healing was possible, e.g., in this case when of polymer film of ≈30 nm was left over the particles . When this critically thin polymer layer is reached, all the low surface energy groups in this layer are already segregated/oriented toward the air or particles interfaces, and hence, the bulk material remaining, no longer has a reservoir (Figure e).…”

Modeling Self-Healing Mechanisms in Coatings: Approaches and Perspectives

“…This occurs despite the fact that systematic computational simulation, based on physically sound and validated mathematical models, provides an additional tool from which to seek material optimization and cost reduction. A clear example of this symbiotic relation between experimental and computational frameworks is given in [23][24][25]. In this group of works, the authors investigate the self-replenishing behavior of damaged films by the rearrangement of low surface energy dangling chains.…”