Improvement of thermal conductivity of novel asymmetric dimeric coumarin liquid crystal by doping with boron nitride and aluminium oxide nanoparticles

Abstract

Coumarin compound-derived dimeric molecules are synthesized and characterized for enhancing the thermal conductivity of liquid crystals. The chemical structures are characterized and confirmed by standard spectroscopic techniques such as FT-IR, 1D and 2D NMR, and elemental analysis. Mesophases were analysed and characterized by the combination of POM, DSC, and X-ray analysis techniques. Most compounds show SmA mesophases upon heating and cooling run except compounds 5b and 5d which are non-mesogenic in the cooling cycle. Mixing coumarin compounds with boron nitride nanosheets (BNNS) and aluminium oxide nanoparticles (Al2O3) dramatically increased the thermal conduction of the liquid crystals (LCs). Doping with 15 wt % of Al2O3 increased the thermal conductivity of LCs from 0.26 W/m K to 0.51 W/m K. While mixing LCs with 35 wt% BNNS increased the thermal conductivity to 0.91 W/m K. The outstanding thermal conductivity of 1.6 W/m K and the specific TCE (per 1 wt% of nanofillers) of ∼12.5% were obtained by mixing LCs with a combination of 15 wt% Al2O3 and 35 wt% BNNS. In addition, the thermal stability of LCs was intensified when doping with nanofillers due to occupying the free volumes between molecules and reducing the overall mobility of the compound. The obtained thermal performance from the prepared LCs nanocomposites of this work illustrated vast potential in specific electronic applications such as photonic systems and solar energy collectors.