Strategies for corrosion protection are required to prolong the life span of metallic structures used by the construction, aerospace, and transport industries. Currently, there are no coatings that can provide at the same time information about the corrosion status of the coated metal and protect the metal against corrosive species and mechanical damage. Herein, triple-functional microcarriers with functions of corrosion sensing, self-healing, and corrosion inhibition are produced and embedded in coatings to prolong the lifetime of metals and enhance the anticorrosion performance of coatings. The microcarriers are prepared by creating Pickering droplets loaded with a corrosion inhibitor and a healing agent and stabilized by silica nanocapsules containing thymol blue as corrosion sensor. The microcarriers are then embedded in a water-based polymer matrix coated on metal substrates. When the coating or metal is mechanically damaged, the healing agent is released from the droplets to hinder further corrosion of the metal. When the local pH value near the metal surface is changing by the generation of hydroxide ion due to the corrosion process, a change of color is detected as well as a release of corrosion inhibitor, leading to a significant decrease of corrosion rate of the coated metal.

A new generation of nanosensors based on mesoporous silica nanocapsules with the ability to monitor the onset of metallic corrosion is successfully developed and tested on 304 stainless steel. The core of the nanocapsules contains water insoluble organic molecules that fluoresce during the anodic dissolution of metallic substrates in the corrosion process. The dispersion of the nanosensors in organic coatings applied on metal substrate allows a very sensitive fluorescent detection of the initiation of metal dissolution, close to defects in the substrate. This promising concept offers therefore new perspectives for the development of smart coatings for corrosion sensing.

A nanonetwork composite coating is prepared for serving as both pH sensor and reservoir for the delivery of functional payload. The composite coating consists in nanofibers containing encapsulated pH‐responsive dye and corrosion inhibitor. The nanofibers are then incorporated in a hydrophobic polymer. While the nanofibers remained intact, they provide additional adhesion strength to the metal substrate. Sensing ability and releasing of active payload are demonstrated by immersing in an artificial corrosive environment and electrochemical impedance spectroscopy measurements. The composite coating can detect the early onset of corrosion and hinders efficiently corrosion compared with passive coatings. This concept paves the way for creating smart coatings that can hinder corrosion progress and allow for an early detection of corrosion before irreversible damages on metallic structures.

Nanostructured multilayered coatings for metals are prepared to simultaneously provide a function of corrosion mitigation and of corrosion sensing for copper substrates. Silica nanocapsules, embedded in one layer of the coating, are used as a host for a corrosion inhibitor and as a sensor, which detect changes of pH value and release inhibitors via an optical signal. Furthermore, another layer in the coating exists in a nanonetwork loaded with another corrosion inhibitor, which is impregnated with a hydrophobic polymer. We demonstrate that a specific arrangement of layers leads to an optimum anticorrosion and sensing performance while the sensing signal can be prolonged for a long time. It is the first time that the fluorophore detecting corrosion is conjugated to the nanosensor and that nanofibers and nanocapsules are used simultaneously to load and release corrosion inhibitors for anticorrosion applications.

A coating is created by incorporating a nanofibrous network, containing an optical sensor and a corrosion inhibitor, in a hydrophobic coating. The nanocomposite displays dual functions of corrosion detection and corrosion inhibition. More details can be found in article number 2001073 by Daniel Crespy and coworkers.