Anyone who’s dealt with hot glue guns is familiar with the long, thin tails of glue they leave behind. 3D printers suffer from a similar problem with the nozzle pulls away from viscoelastic materials like plastics and polymers. Little tails, like the ones seen above, are left behind on the part and must be cleaned away by hand. The source of the trouble is the elasticity of the fluid. Pulling on these liquids stretches them into long thin strands as the molecules inside the fluid resist. But researchers have found an alternate method to break the liquid cleanly: twisting.
When a viscoelastic liquid bridge gets twisted, the liquid undergoes what’s known as edge fracture, an elastic effect that creates an indentation that forces its way inward and breaks the bridge’s connection cleanly. Since the technique only requires spinning the 3D printer’s nozzle when detaching, it should be relatively easy for printer manufacturers to implement! (Image credit: 3D-print – T. Claes, illustration – H. Hill/Physics Today, animation – S. Chan et al.; research credit: S. Chan et al.; via Physics Today)