This can be achieved when printed structural porosity and intrastrand porosity are combined, by adding hollow, gas-filled microspheres into the 3D printing ink. But many researchers are adding different materials to the mix, such as these shape memory polymers, in order to increase the potential applications.
The abstract reads, “Direct ink writing enables the layer-by-layer manufacture of ordered, porous structures whose mechanical behavior is driven by architecture and material properties. Here, we incorporate two different gas filled microsphere pore formers to evaluate the effect of shell stiffness and Tgon compressive behavior and compression set in siloxane matrix printed structures. The lower Tg microsphere structures exhibit substantial compression set when heated near and above Tg, with full structural recovery upon reheating without constraint. By contrast, the higher Tg microsphere structures exhibit reduced compression set with no recovery upon reheating. Aside from their role in tuning the mechanical behavior of direct ink write structures, polymer microspheres are good candidates for shape memory elastomers requiring structural complexity, with potential applications toward tandem shape memory polymers.”
In order to produce the metamaterials, the research team extruded viscoelastic inks, which possess controlled rheological behaviors, through a 250 µm microscale nozzle. The team used an ink that was based in silicone and possessing a polymeric shell. A 3-axis, displacement-controlled 3D printing platform was used in order to create cross-ply structures, so that every layer was perpendicular to the one before it; this type of structure is called a face-centered tetragonal (FCT). The 3D printed structures were 50 x 50 mm, with eight layers, and the material was cured under nitrogen.
The researchers used two different gas microspheres, Tg44 and Tg113, and determined through testing that the Tg44 produced the best results. The metamaterials that contain microballoons filled with Tg44 are very promising, thanks to their shape memory behavior. The team plans to use in-line mixing techniques and multi-material printing to further optimize the structure at a later time. These materials could potentially have commercial applications, if they continue to advance; for example, they could be used in wearable protective padding and cushions, and a person’s body temperature could be used to invoke a recovery response. Discuss in the LLNL forum at 3DPB.com.
[Source: AZO Materials]