pH-sensitive inhibitor release system for corrosion protection
Coatings are broadly used to protect metallic structures from corrosion. However, aggressive acidic and alkaline conditions can both develop locally on the coated metal surface due to corrosion, leading to the failure of the coated structure. Commonly used smart coatings use a timed release of special compounds in response to stimuli experienced during the start of the corrosion process. One important limitation in conventional smart coatings is the ability to react to only acidic or basic pH –thus protecting against either, but not both. Hence, the need for a smart coating capable of providing comprehensive protection against different environmental situations appears critical for many applications.
The design developed here consists of micro/nanocontainers with two weak electrolytes (i.e., polyethylenimine (PEI) and polyacrylic acid (PAA)) that act as corrosion inhibitors. When mixed, electrostatic interaction between the two compounds results in coacervates forming. These coacervates demonstrate different behaviors when low or high pH is present and can effectively prevent or slow corrosion effects of the base structure in both settings. The micro/nanocontainers made from such coacervates with special compounds can be embedded inside a barrier coating and get activated depending on the pH of the environment that the coating is exposed. The capsule size is alterable to achieve enhanced performance in terms of corrosion protection, such as sealing voids that could develop as the inhibitors are consumed. Thus, the invention provides a comprehensive release mechanism embedded into a barrier polymer matrix triggered by either low or high pH.
Extensive use of different metal substrates on the surface of different equipment types benefits from using this invention as an anti-corrosive measure. Surfaces and other areas in automotive, aircraft, liquid transportation vehicles, marine, and medical equipment represent applications where this invention’s novel aspects would be critically beneficial.
In addition to providing corrosion inhibition/protection, the release system can be modified to indicate the presence of corrosion at an early stage. So important elements in an application (e.g., airplane engine blades) are appropriately reinforced or replaced promptly. The design is also easy and inexpensive to manufacture compared with other conventional approaches.