Self-healing adhesion on polymer coatings

Supramolecular self assembling hydrogen bonded polymeric materials are of great importance due to its practical relevance. Well designed molecules based on these concepts can produce polymeric materials with \u93responsive\u94 properties like self healing even in coating application. The reversible, non-covalent hydrogen bonding interactions are a recurring design principle for these materials. Here, we report a concept for repairing mechanical damage at the coating/substrate interface. A dopamine based hydrogen bonded self-healing system was investigated and its use for self-healing adhesion purposes will be discussed. The presence of catechol bonds in the dopamine molecules promotes strong adhesion with the metal surface whereas flexible hydrogen bonding motifs ensure inter/intra molecular hydrogen bonding at the interface with polymer coating. The reversible character of the hydrogen bonds will ensure the repair of the adhesive bonds between the coatings and the substrate upon re-contact at the interface

Modelling of self-healing surface structures coatings

For many current engineering applications the performance of materials depends strongly on the surface properties of the top layer. In many cases a hydrophobic/superphydrophobic top surface is desired (for example for easy-toclean/ self-cleaning applications). The durability of coatings will be substantially extended if the layer which provides the hydrophobic/superhydrophobic property will have ability to self-heal. Previously, hydrophobic coatings with a self-healing surface were reported by our group. These coatings can recover a sufficiently high concentration of the lowsurface-energy groups at the air/polymer interface. The bulk material serves as reservoir of the low-surface energy component (fluorinated polymer dangling chains). A mechanism of self-replenishing involves the reorientation of the dangling chains which carry the fluorinated group. Silica particles where incorporated into the polymer system in order to introduce the surface roughness leading eventually to higher contact angles of the polymer coating. Our goal is to create a model of the a selfhealing superhydrophobic coating. In this work we use the mesoscopic modelling technique (dissipative particle dynamics) in order to study several aspects of these polymer/particle coating: 1) the segregation of the low surface energy groups at the top surface of the coating.; 2) the self-healing response of the system and 3) the dynamics and distribution of crosslinks in the polymer system in presence of relatively large silica particles. For these studies we considered the distribution of the low surface energy groups in a confined geometry at the interfaces available. The minimal thickness of the polymer layer which provides self-healing ability was also calculated. All the relevant parameters (crosslinking conditions, polymer precursor and dangling chain length and distance between particles) were changed systematically. The simulations give a valuable insight into the details of microstructures and dynamics and guide experiments towards the choice of the system with the maximal selfhealing efficiency

Surface repair: Self-replenishing functional polymer coatings

Previously, we reported a self-replenishing polymer surfaces which recover their lowsurface energy (i.e. hydrophobicity), upon surface damage[1]. Following up, we used a dual experimental-simulation approach to understand in-depth the surface segregation of low surface energy components[2], the self-healing mechanism involved on the surface recovery and the influence of different parameters (e.g. mobility of the polymer healing components) on the self-replenishing behaviour. Herein we report our further studies on self-replenishing structured-surfaces. The model self-replenishing polymer system was used to develop robust and easy processing hydrophobic surface-structured coatings, which are able to recover the low surface energy groups at new structured surfaces, created after damage

On the healing mechanism of sol-gel derived hybrid materials containing dynamic di-sulfide bonds

Sol-gel technology is increasingly being used in coatings for corrosion protection and adhesion improvement. So far, the self-healing concept in sol-gel coatings has only been approached from extrinsic healing perspective (i.e. use of nano and micro carriers of corrosion inhibitors) [1]. Despite the benefits of this approach, the damaged area remains open to ambient environment. The implementation of intrinsic healing approaches in sol-gel coatings can thus very well complement current extrinsic ones in order to offer more extended corrosion protection. In the present work the intrinsic healing sol-gel hybrid systems containing dynamic disulfide bonds were developed. The ability of developed systems to restore their cohesion at three different temperatures was evaluated, revealing 70ºC as the optimum healing temperature. In order to get a better understanding of the healing mechanisms, dynamic mechanical thermal analysis (DMTA) was complemented by in-situ raman spectroscopy to follow the evolution of the di-sulfide bonds during the healing cycles. Mechanical properties and content of the broken dynamic bonds were found to be the key parameters in the healing performance of the developed systems. Faster healing kinetics at 70ºC disclosed the dominating role of the breaking/re-joining of the dynamic di-sulfide bonds in the healing mechanism.Aerospace Structures & MaterialsAerospace Engineerin

Understanding the self-replenishing of hydrophobic coatings for further industrial applications

Hydrophobic materials hold many properties that are desirable in coatings, e.g. water repellency and low-adhesion are essential to achieve an easy-to-clean/ self-cleaning behavior. However, most of the coatings currently available cannot maintain their hydrophobicity upon surface damage or wear, due to the irreversible loss of the low surface energy chemical groups. This damage reduces the service-life time of coatings and limits its implementation on industrial applications. Therefore, the recovery of surface chemical groups is crucial for extending the service-life of hydrophobic polymeric coatings. One way to achieve this is to introduce a self-healing mechanism which can replenish the low surface energy groups at the surface after the damage. The proof-of-principle was previously reported for a \u93model\u94 self-replenishing system based on a Poly(urethane) crosslinked soft (low-Tg) network with a small amount of fluorinated dangling chains [1]. In these systems the low surface energy dangling groups can re-orient towards the new air/coating interfaces created upon damaged. In this poster we report further studies in this model Poly(urethane)-based system which allowed us to clarify key details on the dynamics and kinetics of the selfreplenishing mechanism, e.g. the distribution of the dangling chains at the surface and in the bulk [2]. Furthermore, we will also discuss the clear drawbacks identified for the current model system which will restrict its direct industrial applications: 1) weak mechanical properties, e.g. low hardness (due to low Tg) and low solvent resistance. 2) there possibly existed the surface rearrangement due to the presence of hydrophilic ester part in the molecule. So the hysteresis of the coatings were high. 3) the current cross-linking procedure involves high temperature and long curing time