Electric-Potential-Driven Pressure-Sensing Observation in New Hollow Radial ZnO and Their Heterostructure with Carbon

Many applications demonstrated for ZnO desire a high dielectric constant and quickly induced polarization properties with frequency. We present new hollow radial zinc oxide nanostructure and carbon-decorated hollow ZnO heterostructures, which greatly influence the dielectric and capacitive pressure-sensing properties after integrating in polyvinyldine fluoride matrix. The hollow zinc oxide nanostructure was realized by using a simple and cost-effective ambient temperature template-free synthesis process. Crystal structure was investigated by using X-ray diffraction and Raman spectroscopy and then correlated with high-resolution transmission electron microscopy, which reveals buckling of lattice fringes. Mimicking the wurzite structure of ZnO, the developed carbon-decorated hollow radial ZnO improved the dielectric constant ∼140 at 100 Hz and reinforcing efficiency >4 times that of hollow radial ZnO because of strong interfacial polarization. We demonstrated a simple design, fabrication, and testing of flexible polymer composite pressure-sensing device by using such fascinating nanostructures. The capacitive pressure-sensing response is calculated to be 35 times (≤0.002 MPa) and 24 times (≤0.006 MPa) higher than that of the pristine PVDF-based device after poling under corona. Furthermore, the developed devices showed significant capacitive change upon bending because of the displacement of electrodes and change in spacing between the fillers in the polymer matrix

Adsorption of Charge Carriers on Radial Zinc Oxide and the Study of Their Stability and Dielectric Behavior in Poly(vinylidene fluoride)

Radial zinc oxide (ZnO) was prepared using a new user-friendly chemical process, and the surface was modified by adsorbing polyaniline (PANI) as a charge carrier. The modified ZnO (PZnO) was used to prepare poly­(vinylidene fluoride) (PVDF)–PZnO nanocomposites with improved dielectric properties. The structural morphology of the fillers was examined using powder X-ray diffraction and then correlated with observations from high-resolution transmission electron microscopy. A new characterization technique was used to study the maximum adsorption limit by performing solvent relaxation nuclear magnetic resonance experiments, and the results suggested that a maximum of 10% PANI is adsorbed onto the ZnO. The adsorbed PANI acted as an interface and stabilized the ZnO in PVDF solution due to strong interactions between the matrix and fillers. An electron spin resonance (ESR) study was carried out to characterize the spin resonance of ZnO and PZnO. The adsorption of PANI onto ZnO generated charge carriers, and hence, under the influence of a magnetic field, the samples exhibited dissimilar resonance behavior. Dielectric studies of the PVDF–PZnO composites were performed, and the PVDF–ZnO composites and pure PVDF were compared over a wide range of frequencies (0.01 Hz–1 MHz) and temperatures (25–90 °C). The results suggest that the PVDF–7.5PZnO composite showed a significantly improved dielectric constant with a decrease in dielectric loss (0.2), most likely because the adsorption of PANI onto ZnO led to strong interactions between the matrix and fillers and enhanced the interfacial polarization in PVDF

Multiferroic Electroactive Polymer Blend/Ferrite Nanocomposite Flexible Films for Cooling Devices

In recent days, the interest toward the development of multicaloric materials for cooling application is increasing, whereas multiferroic materials would be the suitable alternative to the conventional refrigerants. To explore them, the poly(methyl methacrylate)/poly(vinylidenefluoride-co-hexafluoropropylene) (PMMA/PVDF-HFP) blend and PMMA/PVDF-HFP/Zn0.5Cu0.5Fe2O4 flexible multiferroic nanocomposite films were fabricated by the solution casting method. The structural analyses prove that the strong interfacial interaction between the PMMA/PVDF-HFP blend and the Zn0.5Cu0.5Fe2O4 (ZCF) through hydroxyl (−OH) and carbonyl group bonding with PVDF-HFP enhanced the thermal stability and suppressed the electroactive β phase from 67 to 62%. Experimental results show that 10 wt % of superparamagnetic ZCF nanoparticles with a particle size of 6.8 nm induced both the magnetocaloric and magnetoelectric effects in a nonmagnetic PMMA/PVDF-HFP ferroelectric matrix at room temperature. A set of isothermal magnetization curves were recorded in the magnetic field strength of 0–40 kOe and a temperature range of 2–400 K. The maximum magnetic entropy changes (ΔSM) of −0.69 J·kg–1 K–1 of ZCF nanoparticles and −0.094 J·kg–1 K–1 of PMMA/PVDF-HFP/ZCF nanocomposites showed an interesting table-like flat variation in the temperature range of 100–400 K as a function of the magnetic field. The samples display a large temperature span with a relative cooling power of 293 and 40 J·kg–1 for ZCF and PMMA/PVDF-HFP/ZCF, respectively. The magnetoelectric effect of the PMMA/PVDF-HFP/ZCF composite was proved, but it generated only 1.42 mV/m·Oe in the applied field of 5 kOe. Hence, the entropy change of the present nanocomposite was only due to the magnetocaloric effect, where the magnetoelectric cross-coupling coefficient was negligible. The multicaloric effect could be established if the nanocomposite showed a larger magnetoelectric cross-coupling in addition to the magnetocaloric effect. This approach provides the research findings in functional multiferroic polymer nanocomposites for miniaturized cooling devices