Aggressive environmental factors induce detrimental changes in metals, reducing their strength, as well as thermal and electrical conductivity. To extend the lifespan of metal systems, they are coated with protective films and liquid plastic, alloyed with chromium and titanium, or treated with inhibitors – chemical compounds that slow down the corrosion process. Anticorrosion measures, however, have their limitations: they are expensive, difficult-to-apply, low-efficient, unsustainable, and offer an untimely action when corrosion is already in the active stage.
As a solution, researchers from ITMO University, Tianjin University, and the University of Liverpool proposed polymer microcapsules to efficiently protect metals from corrosion. These capsules adapt to corrosive factors, and in response to a change, they release an active substance to prevent destruction.
These microcapsules consist of a hollow core of silicon oxide crystals and two types of polyelectrolytes – low-molecular bPEI and high-molecular PAA – layered on top. These are compounds of molecules with interconnected repeating structural units, which include groups that are ionizable in solutions. An inhibitor is loaded into the core, protected by a semi-interpenetrating grid structure of polyelectrolytes. A decrease in the pH level of the environment causes the molecular bonds of the polyelectrolyte structure to weaken; its shell opens and releases the active substance. This mechanism gives researchers control over the release process for up to 14 days.
“We didn’t just observe the system and document its “open-close” activities; we calculated the energy profile of changes in the system in response to external stimuli and described its working principles at a molecular level. With our model system, we can use quantum chemistry to calculate how to fine-tune the permeability of the shell and release conditions by changing the composition and architecture of the shell (molecular weights of polymers, number of layers, or the pH level to which the capsules react). This opens up opportunities for creating smart capsules that have even more complex structures and respond to other environmental factors, as well as new programmable smart materials with predicted properties and reversible reactions to external stimuli,” notes Danila Ermolin, an author of the paper and a researcher at ITMO’s Infochemistry Scientific Center.
Another advantage of the developed microcapsules is their high encapsulation efficiency, which is the ratio of the amount of active material incorporated inside a carrier to the overall amount of the material used. For the microcapsules, this value reaches 86%. These structures are also stable, durable, and eco-friendly, which makes them appropriate for industrial-scale production and use.
