Bilayer spin-crossover nanocomposites show robust and controllable actuation cycles upon an electrical stimulus. The anisotropic shape of the particle and the mechanical coupling with the matrix can intensify the work output of the actuators.

We revealed strain (stress) vs. temperature hysteresis loops in spin-crossover@polymer composite actuator materials. The role of the particle-matrix elastic modulus mismatch is highlighted.

We used a spray-coating process to cover silicon microcantilevers with ca. 33 wt% [Fe(Htrz)₂(trz)](BF₄)@P(VDF₇₀-TrFE₃₀) nanocomposite thin films of 1500 nm thickness. The bilayer cantilevers were then used to investigate the thermomechanical properties of the composites through a combined static and dynamic flexural analysis. The out-of-plane flexural resonance frequencies were used to assess the Young’s modulus of the spray-coated films (3.2 GPa). Then, the quasi-static flexural bending data allowed us to extract the actuation strain (1.3%) and an actuation stress (7.7 MPa) associated with the spin transition in the composite.

Spiropyran doped P(VDF-TrFE) nanocomposite films were spray-coated onto silicon micro-cantilevers. We show that switching the molecules from the closed- to the open-ring form by UV light gives rise to a downward bending of the cantilever as well as to a decrease of its resonance frequency. This photoactuation is reversible by means of heating and simultaneous visible light irradiation. From the flexural bending and resonance data, we extracted the actuation strain (0.13 ± 0.03%), stress (4 ± 1 MPa) and elastic energy density (2.3 ± 1 mJ cm⁻³) associated with the photoisomerization of spiropyran molecules in the composite films.

The direct integration of performant permanent magnets (PMs) within miniaturized circuits remains both a scientific and a technological challenge. Magnetophoresis‐driven capillary assembly of hard magnetic nanoparticles is a promising approach to fabricate 3D rare‐earth‐free PMs. However, this process implies the use of soft magnetic blocks to generate the magnetic field gradients required to localize the assembly directly onto silicon substrates. The impact of these soft elements onto the overall magnetic properties is evaluated using Co nanorods as hard material and 150 μm–thick Ni blocks. As expected, the presence of Ni softens the overall properties of the hybrid magnet obtained, but PM properties are preserved for reduced Ni volumes. Magnetic induction as high as 19 mT at a distance of 200 μm is generated by the hybrid Ni–Co–Ni structures, allowing for the electromagnetic actuation of a microelectromechanical resonant sensor.

Spray coating of the ferroelectric polymer P(VDF-TrFE) appears as an attractive approach for the fabrication of electromechanical transducers. However, it is important to elucidate how the crystallinity and the associated piezoelectric properties depend on the coating thickness and additives. To this aim, we have spray-coated various substrates both with pure and nanocomposite films of 70–30% copolymers in a broad thickness range (200 nm–30 μm). Using X-ray diffraction, differential scanning calorimetry, Raman spectroscopy and atomic force microscopy, we show that the obtained films are dense and homogeneous with ca. 50% crystallinity, which consists of a major polar phase, with slight alterations in the sub-micrometer thickness regime. Robust piezoelectricity and ferroelectricity are revealed at room temperature through both local hysteresis loops and lithography experiments using the piezoresponse force microscopy technique. After poling, the piezoelectric d₃₃ coefficient displays values up to −19 and −11 pC N⁻¹ for the pure copolymer and the composite, respectively. For a 33 vol% load of inorganic spin-crossover nanofillers, the switching properties are substantially improved and a coercive voltage of <10 V is demonstrated for micrometric films. Overall, this approach appears as a promising way for the in situ integration of high quality piezopolymer films into complex transducer geometries for sensing, actuating and energy harvesting purposes.