3D Printing of Hydrophobic Eutectogels Toughened by Polymer-Solvent Hydrogen Bonding and In Situ Phase Separation for Capacitive Sensors

Polymer gels are versatile materials in biomedical applications, sensors, and actuators. However, designing gels with diverse functionalities, such as high toughness, self-healing capability, and 3D printability, is often challenging. In this work, it is found that random copolymerization of N-isopropyl acrylamide (NIPAm) with a small amount of acrylic acid (AAc) in a hydrophobic eutectic solvent consisting of menthol and decanoic acid leads to eutectogels toughened by polymer-solvent hydrogen bonding. Interestingly, further increasing AAc content induced phase separation of glassy AAc-riched domain that significantly increased the stiffness of the eutectogels. The stiffness and stretchability of the poly(NIPAm-co-AAc) eutectogels can also be easily modulated by adjusting the AAc content and monomer concentration, leading to highly transparent gels with high toughness. Furthermore, the eutectogels demonstrate efficient dissipation, reasonable recovery, and moderate self-healing capability. The resin is also compatible with digital light processing 3D printing to prepare dielectric layers with different geometric designs for capacitive sensors. By integrating the functions of eutectogels and 3D printing, the approach provides a new avenue for soft materials with a broad palette of mechanical properties and geometrical designs.