4D-Printable, Smart Lubricious Pickering Emulsion Gels Fabricated with Reversibly Assembled Nanogel Surfactants

Gels with high and convertible tribological performance are of great importance for constructing smart devices, sensors, and biomimetic soft matter systems. Of these materials, lubricious gels capable of being manufactured into objects with arbitrary, controllable shapes can exhibit superb adaptability to complex working environments and broader materials design freedoms, but still remain challenging for a number of oleogel and hydrogel systems. Herein, by exploiting a nanoparticle surfactant assembled using N-isopropylacrylamide-methacrylic acid copolymerized nanogel and diamine-terminated polydimethylsiloxane, which can yield near-zero oil/water interfacial tensions and high-strength interfacial films, as both an emulsifier and physical crosslinker, highly stable, viscoelastic, shear-thinning and thixotropic water-in-oil Pickering emulsion gels available for creating various high-resolution 3D-printing patterns and architectures with long-term structural stability and swelling resistance as well as providing favorable macroscale lubrication both in air and under water, can be fabricated. And their lubricious property can be maintained for at least 400 000 continuous reciprocating friction cycles. Further building on the temperature- and pH-controlled reversible assembly of the nanoparticle surfactant, effective shape reconfigurations of the printed gel macrostructures and multilevel switched frictional behavior of the gels can be achieved. Our study may provide new indications for developing novel, versatile, smart, and adaptive soft materials.