Scientists create highly conductive metallic gel for 3D printing at room temperature

Preparing the metal gel

The researchers started with a water-based solution containing tiny micron-scale copper particles.

To create the metallic gel, the team mixed the aqueous micron-scale copper solution with a liquid indium-gallium alloy, which remains in a liquid state at room temperature. As the mixture was stirred, the liquid metal and copper particles adhered to each other, forming a metallic gel network in the solution.

"This gel-like consistency is important because it means you have a fairly uniform distribution of copper particles throughout the material. This does two things. First, it means the network of particles connect to form electrical pathways. And second, it means that the copper particles aren't settling out of solution and clogging the printer," explained Dickey.

The metallic gel, which retains its form after printing, can be successfully produced using a standard 3D printing nozzle. A 3D printing nozzle is the component responsible for precisely depositing the gel material layer by layer to create the desired object. 

After an object is 3D printed, it is allowed to cure. This is the process of letting the 3D-printed object sit or rest after the printing. During this time, the material undergoes chemical or physical changes that enhance its properties, such as solidification, hardening, or bonding. 

The curing process can occur naturally at room temperature or may require specific environmental conditions, such as exposure to heat, UV light, or chemicals, depending on the material used. 

The team found that when their printed object was left to cure at room temperature, it maintained its shape and further solidified. 

Four-dimensional printing

When subjected to heat during the drying process, the team discovered that the alignment of the particles within the material affects how it dries. 

For instance, in the case of a cylindrical object, the sides tend to contract more than the bottom and top. While drying at room temperature does not typically cause structural changes, applying heat, such as placing the object under a heat lamp at 80 degrees Celsius, can lead to predictable structural deformation. 

Controlling the printing pattern and the amount of heat exposure during this phase makes it possible to intentionally alter the object's shape after it is printed, allowing for a four-dimensional printing concept involving the traditional three dimensions plus time.

"Ultimately, this sort of four-dimensional printing is one more tool that can be used to create structures with the desired dimensions. But what we find most exciting about this material is its conductivity.

Because the printed objects are as much as 97.5 percent metal, they are highly conductive. It's not as conductive as conventional copper wire, but it's impossible to 3D print copper wire at room temperature. And what we've developed is far more conductive than anything else that can be printed. We're pretty excited about the applications here," said Dickey enthusiastically.

The researchers are looking to collaborate with industry partners to explore the applications of 3D metal gel printing. 

The findings of the study are published in the journal Matter.