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Droplet Research Indicates Spray Coating Improvement

Wednesday, September 20, 2017

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Researchers based out of the Massachusetts Institute of Technology say they've made a discovery about droplet behavior that could impact the use of spray coatings in certain applications.

The findings note that when droplets come in contact with a surface, thermal properties of the surface have an impact on the droplets’ behavior, meaning that surfaces can be tuned to meet the exact needs of a given application, according to MIT.

Droplet Adhesion

MIT’s findings regarding the thermal properties of a surface were recently published in Nature Physics, authored by MIT associate professor of mechanical engineering Kripa Varanasi, along with former postdoctoral scholar Jolet de Ruiter and and current postdoctoral scholar Dan Soto.

In the study, the team looked at the propertiess of droplets of molten metal freezing onto different surfaces, namely silicon and glass. Traditional assumptions would point in the direction of the droplets behaving the same way on both surfaces, but the researchers’ findings proved otherwise.

“We had two substrates that had similar wetting properties [the tendency to either spread out or bead up on a surface] but different thermal properties,” Varansi noted.

Varanasi Group/MIT

Researchers based out of the Massachusetts Institute of Technology have discovered that, when droplets come in contact with a surface, thermal properties of the surface have an impact on the droplets’ behavior.

Silicon’s heat conducting properties led to the molten metal just falling off, whereas the insulating properties of glass allowed the metal droplets to stick.

By controlling the thermal properties of a given surface, the adhesion of a freezing droplet can be controlled, Varansi noted, adding that this provides “a whole new approach” in determining liquid-surface interactions.

Experimenting with Molten Metal

In experimenting with molten metal, researchers were working with an element that is used in some thermal spray coatings for turbine blades or machine parts. The key to coating uniformity and quality lies in how well each droplet adheres to the surface.

“The way droplets impact and form splats dictates the integrity of the coating itself. If it’s not perfect, it can have a tremendous impact on the performance of the part, such as a turbine blade,” Varanasi said. “Our findings will provide a whole new understanding of when things stick and when they don’t.”

New insights gleaned from this research could help with prevention of droplets sticking, which is imperative for airplane wings in icy weather. According to MIT, this could also lead to the cleaning and waste management of thermal spray processes and additive manufacturing.

The team concluded that changing the thermal properties of the substrate, as well as the temperatures of both the droplets and substrate, have a direct impact on the degree to which the droplets of most any liquid will stick.

“We can imagine scenarios where thermal properties can be adjusted in real time through electric or magnetic fields," Soto said, "allowing the stickiness of the surface to impacting droplets to be adjustable.”

   

Tagged categories: Coatings Technology; Research and development; Spray systems

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