If you played with tangrams in school, this innovation is for you. I saw a video on Twitter of polymer shapes that looked like tangrams and had the ability to move. The polymers they made the shapes out of are called shape memory polymers. If you are curious about how they work, keep reading.
What Did They Invent?
The scientists were able to make the polymers move using a group of materials called shape memory polymers. The team of researchers led by Nicolas Vandewalle in the Group for Research and Applications in Statistical Physics or GRASP published a paper in October 2020. In their paper, they described exactly how they made the polymers move. They termed the technology switchable self-assembled capillary structures.
What Does the Name Mean?
What is Self-Assembly?
Self-assembly is a phenomenon that occurs when materials or objects can spontaneously generate order within a system. In the case of the innovation that we are talking about today, the rhombi that these scientists developed and generated order by coming together and forming shapes.
What is Capillary Action?
The second part of their name, capillary structures, refers to another phenomenon called capillary action. Capillary action is a phenomenon observed in liquids. It describes their ability to flow in narrow spaces without the assistance or resistance of an external force. If you have ever wiped up a spill with a paper towel, then you have benefited from capillary action. The way the water moves toward the paper towel after setting it down is capillary action in motion. The shapes that the scientists created were able to move across the water and form larger shapes. The mechanism they used to move was capillary action, which is why the science termed them capillary structures.
How Did They Make the Shape Memory Polymers?
The scientists used a polycaprolactone (PCL) polymer to make the temperature triggered shape memory rhombi you saw in the video. They poured the polymer into a 3D printed mold of a rhombus. Next, they placed an imprint on top of it that gave each rhombus a concave shape. After the polymer cooled, they removed the imprint. After the cooled rhombus was reheated to a temperature just above the melting temperature. Then they placed a second imprint on the top mold with a convex shape. By taking the rhombi through this process, the scientist programmed a shape memory effect into the polymer rhombi.
How Do the Shape Memory Polymers Work?
By taking the rhombi through that two-step process, they created two orientations. The first concave structure that they programmed created a vertex to vertex orientation. When the rhombi are in water below their programming temperature, the vertex of the shapes is attracted to each other. The shapes that form that connect at the vertex. As long as the water stays below the programming temperature, capillary action makes the rhombi join the vertex.
However, when the water is heated above the programming temperature, the rhombi undergo their shape memory change—the shape transitions from concave to convex in the water. The change causes the larger shape to start separating from the shapes they formed when the vertexes are attracted to each other and form shapes along the edges. The is second orientation edge to edge.
Now how this translates immediately to something that can be used in the real world? I’m not sure but isn’t it cool when a materials science function elevates a childhood toy.