Spot repair or total recoat? The old debate may be reshaped by a new nanocoating that can effectively nip surface damage in the bud, heading off larger problems and the need for a full-scale recoat.
The development may not only lengthen the period between recoats but also improve structural integrity by preventing small fractures from spreading, say polymer scientists and engineers at the University of Massachusetts Amherst, where the work is underway.
University of Massachusetts – Amherst
|A University of Massachusetts illustration shows how nanoparticle-containing capsules roll or glide over damaged substrates, selectively depositing nanoparticle fillers into fractures.|
“This is particularly important, because even small fractures can then lead to structural failure, but our technique provides a strong and effective repair,” says team leader and polymer scientist Todd Emrick.
The potential is significant in a modern world with a “pervasive” need “for rapid, efficient coating and repair mechanisms” in “everything from airplane wings to microelectronic materials to biological implant devices,” Emrick adds.
‘Smart, Triggered’ Release
The work builds on a theoretical prediction by chemical engineer and co-author Anna Balazs at the University of Pittsburgh, UMass Amherst reports.
Emrick notes that at nano-scale, damaged areas typically possess different topography, wetting characteristics, roughness and even chemical functionality than the undamaged surrounding surface.
Using computer simulation, Balazs predicted that “if nanoparticles were held in a certain type of microcapsule, they would probe a surface and release nanoparticles into certain specific regions of that surface,” said Emrick.
Thus arose the vision of capsules probing and releasing their contents in a smart, triggered fashion, known as “repair-and-go,” said Emrick. The mechanism is similar a biological process, such as in white blood cells, he adds.
Gliding and Depositing
The ensuing research delved into the chemistry, physics and mechanical aspects of materials encapsulation and controlled release. Led by Emrick, Alfred Crosby and Thomas Russell, the work involved three polymer materials laboratories at UMass Amherst.
The researchers used a polymer surfactant to stabilize oil droplets in water (in emulsion droplets or capsules). That allowed encapsulation of the nanoparticles in a thin-walled capsule that was able to release them when needed.
“We then found that the nanoparticle-containing capsules roll or glide over damaged substrates, and very selectively deposit their nanoparticle contents into the damaged (cracked) regions,” said Emrick.
The team used fluorescent nanoparticles that clearly showed their selective deposition in the cracked areas, which happily also gave rise to a precise method for detecting damaged substrates, Emrick said.
Moreover, being able to use a water-based system spared the applicator, the environment and the damaged substrate exposure to organic solvents, said the team, which has published its work (“Probing and repairing damaged surfaces with nanoparticle-containing microcapsules”) in the current issue of Nature Nanotechnology.
The next step, says Emrick, is “to demonstrate recovery of mechanical properties of coated objects by adjusting the composition of the nanoparticles being delivered.”
The work was supported by the National Science Foundation’s (NSF) Materials Research Science and Engineering Center on Polymers at UMass Amherst, an NSF Integrative Graduate Education and Research Traineeship (IGERT) award, the NSF Center for Hierarchical Manufacturing, the U.S. Department of Energy, and its Office of Basic Energy Science.