Magnetoelectric effect in flexible nanocomposite films based on size-matching

Magnetoelectric Polymer Membrane-Based Electrical Microenvironment with Magnetically Controlled Antibacterial Activity

The "hard to clean" parts of food processing devices (e.g., the corners of pipes) are difficult to disinfect. This challenge might be overcome through the application of a positive electrical environment. However, the chemical modification of a material surface is complex and difficult. In this work, we developed a smart electroactive Tb_xDy_1-xFe alloy/poly(vinylidene fluoride-trifluoroethylene) (TD/P(VDF-TrFE)) magnetoelectric coating to endow stainless steel with the function of a smart adjustable electrical environment, which was realized by the introduction of a magnetic field of various intensities (0-1800 Oe). An antibacterial assay showed that the polarized coating@stainless steel (P-CS) exhibited antibacterial effects, with the highest antibacterial effect observed at 1800 Oe. Furthermore, in this study, we have, for the first time, explored the antibacterial mechanism of TD/P(VDF-TrFE)-assisted electrical stimulation based on the bacterial intracellular reactive oxygen species (ROS) level, cell respiratory chain, and membrane potential. The results showed that a microelectric field was formed on the P-CS sample in an aqueous solution, which not only generated ROS on the cathode surface but also caused H⁺ consumption in the electrochemical gradient of the bacterial membrane, leading to OH^- production and inhibition of adenosine triphosphate (ATP) synthesis. In addition, the electric field also induced hyperpolarization of the membrane potential in Escherichia coli cells via a K⁺ efflux, thus inducing rearrangement of the outer membrane. In conclusion, an adjustable surface potential was established through the introduction of magnetoelectric polymer coatings, which endowed stainless steel with magnetically controlled antibacterial effects.

Robust Piezoelectric Coefficient Recovery by Nano-Inclusions Dispersion in Un-Poled PVDF–Ni0.5Zn0.5Fe2O4 Ultra-Thin Films

This work aimed to study the influence of the hybrid interface in polyvinylidene fluoride (PVDF)-based composite thin films on the local piezoelectric response. Our results provide evidence of a surprising contradiction: the optimization process of the β-phase content using nano-inclusions did not correspond to the expected nanoscale piezoelectric optimization. A large piezoelectric loss was observed at the nanoscale level, which contrasts with the macroscopic polarization measurement observations. Our main goal was to show that the dispersion of metallic ferromagnetic nano-inclusions inside the PVDF films allows for the partial recovery of the local piezoelectric properties. From a dielectric point of view, it is not trivial to expect that keeping the same amount of the metallic volume inside the dielectric PVDF matrix would bring a better piezoelectric response by simply dispersing this phase. On the local resonance measured by PFM, this should be the worst due to the homogeneous distribution of the nano-inclusions. Both neat PVDF films and hybrid ones (0.5% in wt of nanoparticles included into the polymer matrix) showed, as-deposited (un-poled), a similar β-phase content. Although the piezoelectric coefficient in the case of the hybrid films was one order of magnitude lower than that for the neat PVDF films, the robustness of the polarized areas was reported 24 h after the polarization process and after several images scanning. We thus succeeded in demonstrating that un-poled polymer thin films can show the same piezoelectric coefficient as the poled one (i.e., 10 pm/V). In addition, low electric field switching (50 MV/m) was used here compared to the typical values reported in the literature (100–150 MV/m).