These objects acquire the ability to adapt to their environment or are programmed to evolve in a controlled manner under the effect of external stimuli (temperature, light, electric or magnetic field, etc.).
In this context, LSI researchers are particularly interested in the fabrication of magneto-active polymers by 3D printing.
First, they used experiments and simulations to systematically study how magnetite nanoparticles (Fe3O4, up to 6 wt%) self-assemble into wire-like structures within photosensitive resins (urethane-acrylate with a reactive butyl acrylate diluent). The mechanical properties of the photo-cured polymers can then be adjusted by modifying the resin composition, and the magnetic response can be modulated by varying the nanoparticle loading of the printed layer.
Once the configuration is chosen, the photosensitive resin is exposed to a light source (UV or visible) under a magnetic field. Its photo-curing stabilizes the embedded magnetic micro-wires and endows the printed layer with a magnetic anisotropy in a well-defined direction. This property can then be used to control the behavior of the printed macroscopic object (folding-unfolding, rotation, etc.).
In practice, the scientists modified a commercial digital light processing (DLP) 3D printer so that they could apply a magnetic field of varying intensity and direction for each 3D printing layer.
They thus made a series of objects showing "programmed behavior", such as actuators that rotate or bend on command. They also combined magnetic wheels with non-magnetic elements to create complex assemblies, such as linear actuators or active clamps.
The next step will be to introduce new chemical species into the photosensitive resin, in order to print a multifunctional material that has both magnetic and plasmonic properties.
Furthermore, the researchers will focus on transposing this additive manufacturing protocol to smaller (micrometer-scale) objects, such as metamaterials, using "two-photon printing". This new project (Quattro-D) will be financed by the CEA's 2021 cross-disciplinary skills program. Strictly speaking, it will be the first 4D printing project at the CEA.
This work was carried out in collaboration with the Politecnico di Torino (Italy) and CentraleSupelec (Université Paris Saclay).