Robust and Self-Healable Bulk-Superhydrophobic Polymeric Coating

Recovery of the compromised antifouling property because of perturbation in the essential chemistry on top of the hierarchical topography of a superhydrophobic coating is commonly achieved through some stimuli (temperature, humidity, pH, etc.)-driven reassociation of the low surface energy molecules. However, self-healing of superhydrophobicity in physically damaged materials having inappropriate topography is difficult to achieve-and extremely important for the practical utility of this bioinspired property. Recently, very few materials have been introduced-that are capable of recovering the hierarchical features-but only after the application of appropriate external stimuli. Further, the optimization of appropriate stimuli is likely to be a challenging problem in practical scenarios. Here, we have strategically exploited a simple and robust 1,4-conjugate addition reaction between aliphatic primary amine and aliphatic acrylate groups for appropriate and covalent integration of a modified-graphene oxide nanosheet-which is well recognized for its exceptional mechanical properties. The synthesized material exhibited a remarkable ability to protect the antifouling property from various harsh physical insults, including physical erosion of the top surface of the polymeric coating and various physical manipulations etc. However, after application of pressure on the same polymeric coating, the bioinspired, nonadhesive (contact angle hysteresis < 5 degrees) superhydrophobicity was compromised, and the physically damaged polymeric coating became highly adhesive (contact angle hysteresis similar to 50 degrees) and superhydrophobic. But, after releasing the pressure, the native nonadhesive (contact angle hysteresis < 5 degrees) extreme wettability was self-restored in the polymeric coating through recovery of the essential hierarchical topography-without requiring any external stimulus. This unique material, having impeccable durability and absolute self-healing capability, was further explored in (i) developing rewritable aqueous patterns on the extremely water-repellent surface and (ii) selective impregnation of water-soluble agents on the surface of polymeric coating-without any permanent change in the extreme water repellency property. The unique self-healing process eventually provided a superhydrophobic print-that was made out of hydrophilic small molecules. This printing was performed directly from an aqueous medium, which is extremely hard to achieve using the conventional superhydrophobic materials. Such multifunctional interfaces could be an important avenue for various smart applications, including delivery of hydrophilic small molecules, catalysis, self-assembly of colloids, reusable chemical sensing, etc.