3D printing of transparent silicone elastomers

Additive manufacturing is essential to the production of advanced materials, providing a straightforward approach to rapid prototyping and manufacturing. Direct ink writing (DIW), a subset of additive manufacturing, offers a versatile route to ink extrusion—a processing method where a viscous ink is forced through a nozzle but behaves like a solid when printed on a substrate. Polysiloxanes, a subcategory of polymers, are a useful class of materials that can be printed via extrusion and exhibit excellent thermal and mechanical properties. Polysiloxanes are particularly useful for their optical transparency. However, when using DIW to print polysiloxanes, they must be mixed with the appropriate additives, i.e., rheological fillers, which can affect the material’s optical transparency.

In a study featured on the front cover of the May 2022 issue of Advanced Materials Technologies, a multi-disciplinary team of LLNL scientists developed a polysiloxane formulation that can be printed into transparent elastomeric structures. The team found that transparency depends primarily on refractive index (RI) matching—indicating the light bending ability of a medium—which is also dependent on temperature. Transparency may increase or decrease as temperature increases, depending on the RI mismatch of the base polysiloxane and silica. This means that to produce transparent inks, it is critical that the RI of the base polysiloxane matches the RI of the rheological fillers. By controlling the rheological properties and printing parameters, researchers were able to produce printed materials with suitable optical transparency. With a growing demand for advanced materials and architectures in applications such as stretchable electronics, optics, healthcare, and soft robotics, the transparent formulations described in this work could fulfill specific needs for functional elastomers.

[M.J. Ford, C.K. Loeb, L.X. Pérez Pérez, S. Gammon, S. Guzorek, H.B. Gemeda, A.M. Golobic, A. Honnell, J. Erspamer, E.B. Duoss, T.S. Wilson, and J.M. Lenhardt, 3D Printing of Transparent Silicone Elastomers, Advanced Materials Technologies (2022), doi: 10.1002/admt.202100974.]