Researchers in the laboratory of Christopher Bates, associate professor of materials at UC Santa Barbara, and Michael Chabinyc, professor of materials and chair of the department, have teamed up to form the first 3D-printed “brushbrush” elastomer develop. The new material results in printed materials that have unusual softness and elasticity – mechanical properties that are very similar to those in human print.
Conventional elastomers, i.e. rubbers, are harder than many biological fibers. This is due to the size and shape of their proportional polymers, which are long, linear molecules that react easily as cooked spaghetti. In contrast, brushless polymers have additional polymers attached to the linear spine, resulting in a more bottle-like structure you would find in your kitchen. The polymer structure of a bottle brush enables the formation of extremely soft elastomers.
The ability to print 3D bottle brush elastomers makes it possible to accelerate these unique mechanical properties in applications that require careful control of the dimensions of objects ranging from biomimetic material to high-sensitivity electronic devices, such as friction pads , sensors and actuators.
Postgraduate researchers – Renxuan Xie and Sanjoy Mukherjee – played two key roles in the development of the new material. Their findings were published in the journal Advances in science.
Xie and Mukherjee’s main finding involves the self-assembly of bottle-brush polymers at the nanometer-long scale, which causes a hard-to-liquid transition in response to activated pressure. This substance is classified as a weight-bearing liquid, meaning that it begins as a semi-soft substance that holds its shape, like butter or a toothpick, but when pressed sufficiently, it liquefies and can be squeezed through a syringe. The team takes advantage of this premise to create ink in a 3D printing process called direct ink printing (DIW).
The researchers can adjust the material to flow under different amounts of pressure to suit the processing conditions you want. “For example, you may want the polymer to retain its shape under a different pressure level, such as when vibration is present,” Xie says. “Our material can hold its shape for hours. That’s important, because if the materials bag at the time of printing, the printed part will have poor structural stability.”
As soon as the item is printed, UV light is applied to cross-linked links that Mukherjee inserted and incorporated as part of the ink design. The binding crosses can bind between adjacent bottle brush polymers, resulting in a very soft elastomer. At that point, the material is going to be a durable durable material – it will no longer be under pressure – and it exhibits amazing properties.
“We start with long polymers that aren’t cross-linked,” Xie said. “That allows them to flow like liquid. However, after you illuminate the light on them, the small molecules between the polymer chains react and are bound together in a network, so you have a solid, an elastomer that which, when stretched, returns to its original form. “
Soft material is measured by its model, and for most elastomers, it is relatively high, meaning that their stiffness and elasticity are similar to those of a rubber band. “Our material model is a thousand times smaller than a rubber band,” notes Xie. “It’s incredibly soft – it feels very much like human cloth – and very stretchy. It can stretch about three or four inches long.”
Disaster Ink
Mukherjee accidentally discovered the material, while trying to develop material for a different project, one that would increase the amount of cost that an actuator can store. When the elastomer came to Xie for character, he knew immediately that it was special. “I could immediately see that it was different, because it could hold its shape so well,” he recalled.
“When we saw this really great product pressure, it went down on everyone together that we could 3D print,” Bates said, “and that would be cool, because the masterpiece isn’t here’s a 3D we know about. -soft property.
Brush polymers have been around for over twenty years. However, Bates said, “The field has exploded in the last decade thanks to advances in synthetic chemistry that provide tremendous control over the size and shape of these unique molecules.
“These super-soft elastomers may be relevant as implants,” he said. “You may be able to reduce swelling and rejection with the body if the mechanical properties of an implant match a native tissue.”
Another important element of the new material is that it is a real polymer, Chabinyc noted.
“They don’t have water or other solution to make them artificially softer,” he said.
To understand the importance of not containing water in the polymer, it is useful to consider Jell-O, which is mostly water and retains its shape, but only as long as the water stays. inside. “If the water was gone, you would just have shapeless stuff,” Chabinyc said. “With a conventional polymer, you have to figure out how to keep the right amount of water in it to maintain its structure, but this new material is all solid, so it will never change.”
In addition, the new material can be 3D printed and processed seamlessly, which is also unusual. “People often add solvent to a solid melt until it is squeezed out of a nozzle,” Xie said, “but if you add a solution to it, it has to evaporate after printing causing the object to change. shaped or cracked. “
Mukherjee said, “We wanted the material and the printing process to be as clean and easy as possible, so we played a chemistry trick with flexibility and self – assembly, which left the process unsolvable. The fact that we are not, the use of a solution is a great advantage. “