Linear Low Density Polyethylene-Thermotropic Liquid Crystal Composite Substrate for High-Frequency Devices: Dielectric Characterization

Composite substrates of linear low-density polyethylene with thermotropic liquid crystals as inclusions with three different weight fractions were synthesized. The dielectric characterizations of the composites in X band frequencies were studied to assess their applicability as substrates for microwave devices. Thermotropic liquid crystals, NN-(terephthalylidene)bis(4-n-butylaniline), NN-(terephthalylidene)bis(4-n-hexylaniline) and NN-(terephthalylidene)bis(4-n-decylbenzamine) were synthesized in the laboratory at room temperature. Structural characterization for synthesized thermotropic liquid crystals was done using nuclear magnetic resonance and Fourier transform infrared spectroscopy. To confirm the distribution of liquid crystal inclusions in the polymer matrix, scanning electron microscope images were used. Water absorbance test was carried out following Archimedes’ principle. The real part of complex permittivity and the dielectric loss tangent at X band frequencies for all the weight fractions of the composite were found to be ~ 2.1–2.4 and ~ 10⁻²–10⁻⁴ respectively. The magnetic loss tangent was also measured for the substrates and showed values within the range of 10⁻¹–10⁻². To establish the suitability of the fabricated substrates for use in antennas, the return losses were calculated using the complex permittivity and permeability values.