Oxidation, in its many forms, can be a double-edged sword; a boon or a bane to humanity. Think of the comforting warmth derived from burning wood or the propulsion in electric vehicles that simplifies travel sustainably, which are both underpinned by the same process.
Yet, this very phenomenon, when it affects metals—materials foundational to the advancement of human civilisation—translates to the pervasive and global challenge of rust, an issue that is not only aesthetically displeasing but can also pose major risks.
The implications of rusting are vast. It compromises infrastructure integrity, shortens the lifespan of tools and machinery, and has profound economic impacts due to repair and replacement costs. Not to mention the human cost. Each year, numerous bridges succumb to corrosion-induced damages and failures, leading not only to significant economic losses but also, tragically, to fatalities.
The question then arises: Why is it so difficult to get rid of rust?
Conventional methods starve off corrosion by encapsulating metals within protective coatings. However, this straightforward solution is not impenetrable. Despite the barrier, minute molecules of oxygen and water can still seep into the coating material and cause rusting, while initiating a chain reaction that exacerbates the oxidation of the metal.
Researchers at the National University of Singapore (NUS) Institute for Functional Intelligent Materials (I-FIM) are doing more than just stopping rust in its tracks—they’re building “nano-sized corrosion time machines”.
In their innovative approach, NUS I-FIM researchers are not just preventing the penetration of oxygen but are actively managing the reaction at the metal’s surface.
Like many chemical reactions, oxidation is reversible. “If a material can be oxidised, it can also be reduced, though this is often a slow and barely perceptible process,” explained Professor Konstantin Sergeevich Novoselov, Director of NUS I-FIM. “La Chaterlier’s principle tells us that when a system in balance is disturbed, it tries to counteract that change. So, by increasing the amount of reduction agent, we can accelerate the process of reduction.”
A breakthrough in this area is the use of nanomaterials. These materials, thousands of times smaller than human hair, can function both as sensors to detect the onset of oxidation and as triggers to release the reducing agent precisely where and when it’s needed.
The researchers at NUS I-FIM developed a “nano-capsule” made of halloysite, a naturally occurring aluminosilicate clay, that is loaded with a reducing agent. It is then enveloped in a composite blend of graphene and polyelectrolyte, which is calibrated to unwrap upon detecting an excess of protons, a corrosion by-product. This targeted approach ensures that the reducing agent acts exactly at the inception of corrosion, stopping and even rolling back any damage. These nanomaterials can also be arranged as a dense array on metal surfaces given their extremely small sizes.
As the cherry on top, the synthesis of these nano-capsules was designed with efficiency and sustainability in mind. It harnesses the principle of self-assembly—a process where starting molecules spontaneously organise into structured arrangements, which are the nano-capsules in this context.
“In the face of environmental and economic challenges posed by corrosion, smart nanomaterials are emerging as super soldiers in our efforts to combat rust,” remarked Prof Novoselov.
However, the potential of programming materials at the nanoscale transcends beyond rust prevention. “From targeted drug delivery to localised energy sources to novel security solutions such as indelible document prints or signatures, the application of smart nanomaterials introduces limitless possibilities in the phygital (physical and digital) space,” added Prof Novoselov.