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Painting is a cost-effective technique to delay the onset of corrosion in metals. However, the protection is only temporary, as corrosion begins once the coating becomes scratched. Thus, an increasingly common practice is to add microencapsulated chemical agents to paint in order to confer self-healing capabilities. The additive's ability to protect the exposed surface from corrosion depends upon (i) how long the chemical agent takes to spread across the exposed metal; (ii) how long the agent takes to form an effective barrier layer; and (iii) what happens to the metal surface before the first two steps are complete. To understand this process, we first synthesized 23 ± 10 μm polyurea microcapsules filled with octadecyltrimethoxysilane (OTS), a liquid self-healing agent, and added them to a primer rich in zinc, a cathodic protection agent. In response to coating damage, the microcapsules release OTS into the scratch and initiate the self-healing process. By combining electrochemical impedance spectroscopy, chronoamperometry, and linear polarization techniques, we monitored the progress of self-healing. The results demonstrate how on-demand chemical passivation works synergistically with the cathodic protection: zinc preserves the surface long enough for self-healing by OTS to reach completion, and OTS prolongs the lifetime of cathodic protection.

We describe a method for fabricating biologically inspired hierarchical surfaces in a single step through surfactant self-assembly at an oil/water interface. The key to this system is the use of polydimethylsiloxane-diacrylate for the oil phase, which makes it possible to solidify these delicate structures with UV photocuring. Scanning electron microscopy (SEM) and 3-D optical profilometry reveals morphologies that capture the randomness, fractal geometry, and hierarchical organization of natural materials. The morphology is controlled by surfactant type, surfactant concentration, viscosity, film thickness, and time. The experimental evidence is consistent with a spontaneous increase in surface area driven by a transiently negative surface tension. Spontaneous emulsification generates distinct morphologies for a given surfactant and surfactant concentration in a manner reminiscent of phase behavior in a ternary phase diagram. When emulsification cannot keep pace with the increase in surface area, buckles form. These perturbations are then amplified at increasing length scales by dewetting and the Rayleigh-Taylor instability.

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