Unveiling the anisotropy and mechanism of magnetic alignment of graphene in polymer composites for efficient absorption of THz radiations (0.3–3.0 THz)

Abstract

Flexible polymer films containing highly aligned graphene flakes were designed using low magnetic field for Terahertz (THz) shielding applications. The alignment of graphene resulted in a unique dark-bright field macroscopic patterns on the cured composite films. On a microscopic scale, the alignment of graphene resulted in a distinctive chain-like structure that favour an effective electron flow path resulting in an electron mobility and optimal electrical conductivity of 7.2 cm²/Vs and 3.3 x 10⁻⁷ S/cm, respectively, which is extremely higher than the homogenous composite for the lowest graphene loading of 1 wt%. For the first time, an aligned composite film of 100 μm thickness was characterised using the synchrotron beam in the THz regime – 0.3 to 3.0 THz and exhibited an exceptionally high absorptance of 56.6 % of T-rays for 1 wt% graphene concentration. Simultaneously, the mechanism of orientation and the in-situ alignment of graphene in the magnetic field was characterised using the time-of-flight small angle neutron scattering technique and their probability of alignment, anisotropy factor were estimated. The in-situ neutron experiments indicate that when the applied magnetic field is perpendicular to the wave vector of the incoming neutron beam, a pronounced anisotropy is observed in the total unpolarized beam due to the alignment of graphene flakes. The exploration of magnetic alignment of graphene and determination of optical anisotropy lays foundation for further discovery of aligned graphene-based composite. The outstanding performance and high efficiency of aligned graphene composites present a huge potential in THz devices, polarization control and shielding solutions for T-rays.