Understanding the dielectric properties and electromagnetic shielding efficiency of zirconia filled epoxy-MWCNT composites

In the present study, hybrid composites are prepared by reinforcing various concentrations of high permittivity zirconia nanofiller into epoxy/CNT compositions to test their usability in EMI shielding applications in the X and Ku bands. ZrO2 nanofiller is added in different proportions to improve absorbance shielding while maintaining the composite conductivity uniform by adding constant CNT concentration to restrict the reflectance shielding. The microscopic studies have revealed an efficient dispersion of ZrO2 nanoparticles in the CNT networks and provided a smoother surface. The presence of zirconia nanofillers increased the dielectric properties, viz. the dielectric constant (194 at 0.1 Hz) and loss tangent (1.57 at 0.1 Hz), respectively, whereas the conductivity was found to be invariantly constant. The increased permittivity of composites enhanced the shielding by absorption, while the shielding by reflection is least influenced by the addition of zirconia nanofiller. The addition of zirconia nanofillers increased the permittivity and tan delta, allowing charges to accumulate at the interfacial areas for incoming EM radiations, resulting in increased absorbance shielding. Limiting the CNT concentration in all composites to the same level resulted in the formation of conductive networks, thus resulting in uniform reflectance shielding for all the hybrid composites in the present study. The dynamic mechanical analysis showed the improvement in the storage modulus and activation energy due to the enhanced interfacial adhesion and cross-linked polymer density.

Cyanate Ester Resin/Silica subnanocomposites and their superiority over nanocomposites due to fundamental role of constrained interfacial dynamics

The study of nanostructure, thermal and relaxation properties (by HAADF-STEM, EDXS, DMA and DSC), combined with the calculations of interparticle distances and interfacial areas, has been performed for a series of the hybrid Cyanate Ester Resin (CER)/Si02 polymer composites with 0.01 to 10 wt.% Si02 units introduced via a sol-gel process. The absence of clusterization, arising only subnanometric Si02 nodes and their quasi-regular distribution within the amorphous matrix, with the shortest distances between nodes, provided their exceptional positive impact on the matrix properties at ultra-low Si02 contents of 0.03-0.1 wt.%. The superiority of these subnanocomposites over the nanocomposites was determined by the role of constrained interfacial dynamics over the whole matrix.

Discrete One-Stage Mechanochemical Synthesis of Titanium-Nitride in a High-Energy Mill

Discrete (discontinuous) mechanochemical synthesis of titanium nitride was experimentally investigated. The experimental results show that mechanical activation intensifies the chemical conversion in the Ti-N system, and the discrete synthesis of the final product is conducted under “soft” controlled conditions without high heat release. The new theory of mechanochemical synthesis and the mathematical model based on it were used for theoretical evaluation of the dynamics of titanium activation in the nitrogen medium. It was found that the discrete mode of synthesis includes two factors accelerating mechanochemical reactions in the Ti-N synthesis: structural (grinding of metallic reagent and formation of interfacial areas) and kinetic (accumulation of excess energy stored in the formed structural defects in metallic reagent). The kinetic constants of the process were found using experimental data and the inverse problem method. The diagrams defining the controlled modes of obtaining titanium nitride particles with the given characteristics were constructed. A mathematical model for theoretical estimation of the dynamics of activation of titanium powder in the nitrogen medium was developed using a new macrokinetic theory of mechanochemical synthesis.

Quantitative 3D imaging of partially saturated granular materials under uniaxial compression

Gauging the mechanical effect of partial saturation in granular materials is experimentally challenging due to the very low suctions resulting from large pores. To this end, a uniaxial (zero radial stress) compression test may be preferable to a triaxial one where confining pressure and membrane effects may erase the contribution of this small suction; however, volume changes are challenging to measure. This work resolves this limitation by using X-ray imaging during in situ uniaxial compression tests on Hamburg Sand and glass beads at three different initial water contents, allowing a suction-dependent dilation to be brought to the light. The acquired tomography volumes also allow the development of air–water and solid–water interfacial areas, water clusters and local strain fields to be measured at the grain scale. These measurements are used to characterise pertinent micro-scale quantities during shearing and to relate them to the measured macroscopic response. The new and well-controlled data acquired during this experimental campaign are hopefully a useful contribution to the modelling efforts—to this end they are shared with the community.

Bipolar membrane polarization behavior with systematically varied interfacial areas in the junction region

Left image is the relationship for the overpotential for water dissociation as a function of bipolar junction electric field whereas the right image presents micrographs and the procedure to make bipolar membranes with micropatterned interfaces.