All-Silicone 3D Printing Technology: Toward Highly Elastic Dielectric Elastomers and Complex Structures

Silicone elastomers have been shown to be well-suited for dielectric elastomer actuators (DEA), mainly due to their unique combination of properties such as, high elasticity and reliability, fast electromechanical response, and high thermal stability. 3D printing of silicones can be achieved by employing either costly and sensitive metal catalysts, low-viscosity precursors with complex chemical structures that are sometimes difficult to reproduce, or rheological modifiers or by incorporating reinforcing fillers (e.g., silica). Here, we present a formulation for 3D printing consisting only of α,ω-bis(trimethyl­siloxy)­poly(dimethyl­siloxane-co-methylthio­propylsiloxane) with a molecular weight M_n = 55000 g/mol (much higher than what the literature reports) and 9.1 mol % vinyl groups as the base polymer and α,ω-bis(trimethylsiloxy)­poly(dimethyl­siloxane-co-methylthio­propyl­siloxane) with M_n = 7000 g/mol and 5 mol % thiol groups as a cross-linking agent, along with 2,2-dimethoxy-2-phenyl­acetophenone (DMPA) as the photocatalyst, showing the optimal thiol/vinyl molar ratio of 0.047. The impact of UV exposure time on the proposed cross-linking system was investigated via FTIR spectroscopy and compression tests, revealing fast curing rates and gelation times of less than 1 s. As a demonstration, the printing platform produced a rubber grid consisting of 24 printing layers that can endure 100 compressive cycles at 50% strain without hysteresis. Moreover, the 3D-printed silicone ink generates elastomers with an elongation at break of 221%, a Young’s modulus of 0.29 MPa, and a stress decay <2% when subjected to 200% strain for 100 min, while the electromechanical tests reveal a maximum actuation strain of 9.5% at an electric field of 41 kV/mm. Our approach may open pathways for processing soft materials with unique geometries for medical devices, soft actuators, haptics, and beyond.