Fabrication and radio frequency characterization of high dielectric loss tubule-based composites near percolation

Abstract

Microscopic lipid tubules with an average aspect ratio (length/diameter) of approximately 12 were metallized electrolessly with copper or nickel-over-copper, and mixed with vinyl to make foot-square composite dielectric panels. As loadings increased the metal tubule composites displayed an onset of electrical percolation with accompanying sharp increases in real and imaginary permittivities. Gravity-induced settling of the tubules while the vinyl was drying increased true loading density at percolation threshold for nickel/copper tubules to ∼12 vol %. This threshold was at a significantly lower loading density than that previously measured for percolation by composites containing spherical conducting particles. Qualitatively, the shape of the composite permittivity versus loading density curves followed predictions by the effective-mean field theory for conducting stick composites. Changes in permittivity of the vinyl panels were observed for several days after fabrication, and were apparently associated with solvent evaporation from the matrix.

Development of polyurethane multiwall carbon nanotubes (MWCNTs) novel polymeric nanodielectric material

“…The number of special features has been reported on polymer/MWCNTs nanocomposites in literature such as excitation of localized electronic states resulting in high intrinsic permittivity [11]. The microwave permittivity is found to be exhibited linear frequency dependent [12,13]. These results are demonstrated the scope for obtaining polymer/MWCNTs nanodielectrics with microwave properties which are more diverse than those obtainable with other types of carbon fillers, e.g., with various types of dispersive dielectrics, with high dielectric constant but having relative low tangential loss, and tunable dielectric under small bias voltage [14].…”

Shift of resonance frequency of long conducting fibers embedded in a composite

“…1 Due to the high dielectric constant ͑real part of the permittivity͒, the fiber composites can be useful as highpermittivity, low-loss materials for applications in dielectric resonators, antennas, etc. 2 If the imaginary part of the permittivity is high, the composite will exhibit strong dielectric dispersion that is useful in developing various frequency selective microwave materials, such as frequency selective surfaces ͑FSS͒ ͑Ref. 3͒ and multilayer coatings for impedance matching.…”

“…1 and 8, and references therein͒ and experimentally. 2,4,11,12 In the calculation of the effective permittivity of composites, e ϭ e Јϩi e Љ , the averaged polarizability of the inclusions is assumed to be equal to the polarizability of a homogeneous medium with the permittivity e . If the volume concentration of the fibers in a fiber composite is small, this assumption leads to the well-known dilute limit approximation equation:…”

Chiral Molecular Self‐Assembly

“…Novel composites containing such metal-clad tubules are currently being produced commercially for use as high-dielectric-loss materials. 28 Metal-coated tubes have also successfully been demonstrated for long-term controlled-release applications in nonmedical scenarios. 29 …”