Self Peeling Droplets: Can Droplet Control Help Improve 3D Printing?

MIT researchers Kripa Varanasi, Jolet de Ruiter, and Dan Soto have recently published a paper in Nature Physics detailing how they can control the adhesion of droplets on surfaces. By changing the thermal properties of a surface, the team has found that they can control if the droplet falling onto that surface will stick, bounce or peel away. By controlling when things stick and when they do not, they think that they may be able to help the surface coatings industry and 3D printing. They created a map which outlines what droplets do based on the drop itself, temperature and substrate effusivity (substrate means underlying layer and thermal effusivity is a number used to measure how good two materials are at the dissipation or storage of heat when they come into contact with each other).

The team first got onto this when they witnessed self-peeling droplets of metal detach from surfaces via a high-speed thermal camera. According to Soto:

“Since the degree to which droplets stick or don’t depend on a material’s thermal properties, it’s possible to tailor those properties based on the application. We can imagine scenarios where thermal properties can be adjusted in real time through electric or magnetic fields, allowing the stickiness of the surface to impacting droplets to be adjustable.”

The team can tweak the adhesion and deformation of the droplets as well. Another way they could do this would be to change the temperatures of the droplets and the surface relative to each other. This indeed could be very exciting for 3D printing. If you could adjust these droplets on the fly, then it is easy to think that you could make strides in surface adhesion in coatings or with new 3D printing technologies. Imagine a self-peeling metal 3D printing technology where support would only temporarily adhere to parts. Or imagine metal 3D printed parts with relatively easy to remove supports. One could also perhaps have a thin film 3D printing process whereby the surface would be continually altered to change the droplets that fell on it. Professor Varanasi has previously done research how to reduce contact time in bouncing droplets and heads the eponymous research group at MIT that looks specifically at surface coatings. He has some patents and lots of papers on surface wetting specifically.

A Self-Peeling Droplet

The startup DropWise, which aims to produce energy efficient coatings for the power industry, is a product of Varanasi’s lab as well. For inkjet 3D printing technologies such as those developed by Digital Metal, Desktop Metal and HP, droplets and how they adhere could also be of paramount importance. Desktop Metal itself was founded by a softball team’s worth of MIT faculty that may be interested in what Professor Varanasi and company are doing. Powder Bed Fusion, Directed Energy Deposition, and other metal 3D printing technologies are also always going to be curious as to how droplets of metal react and can react. Cold Spray 3D printing applications and energy deposition processes where powder is sprayed or deposited would find this an interesting piece as well.

But could this perhaps point to an entirely new 3D printing technology? If one could change how drops adhered and do this in a very controlled way then you could, through a kind of “variable heat build plate,” control at each location what each droplet did. So a droplet dispensing system could then pass over a plate, and each of the droplets could be “designed” on the fly. This would be a fascinating thing indeed. I see a lot of potential in combining this with a coating application for 3D printed parts.

Professor Varanasi going for the Bond villain look.

Professor Varanasi also has a patent on lubricating implants, and so he would understand the nature of lubricating implants. Many of these types of implants are currently 3D printed. To be able to use this in conjunction with the patented research to “lubricate on the fly” while manufacturing a part would be very interesting indeed. If one could design the droplets on the fly once they hit the powder bed or inkjet 3D printed part, then custom coatings and textures could be applied to it in these processes as well. This would most likely be a post-processing step which could then have a high degree of influence and individual variability as to what the final coating needed to be. One could even envision destressing parts in this way as well.

It is still very early for us to really have any idea if this research will impact our industry. It may very well not play a part at all. We should keep our eyes and ears open, however, to research affecting our industry, even in the broadest most oblique ways. Virtually anything that can be liquid and then become solid can be printed, anything that can be sintered can be printed and anything that can be bound together can be printed. This means that we have a huge number of different materials and interactions that could lead to new 3D printing processes. Will this be one of them?

Let us know what you think at 3DPrintBoard.com or in the comments below.