Liquid crystalline behaviour of new dimers containing coumarin and biphenyl moieties and enhancement of their thermal conductivity: liquid crystal-nanoparticles

ABSTRACT

To develop advanced heat transfer composites, new sets of unsymmetrical calamitic molecules with a coumarin unit at one end and a biphenyl group at the other end were synthesised. Their structural characterisation was investigated by routine techniques such as CHN analysis, and FT-IR, and 1D, and 2D NMR spectroscopic techniques. The liquid crystalline properties of these molecules were investigated by POM and DSC along with XRD techniques. All target compounds exhibited mesomorphic behaviour. The smectic C phase was seen for all the compounds. To enhance their thermal conductivities, conductive nanofillers, such as boron nitride nanosheets (BNNSs) and aluminium oxide nanoparticles Al₂O₃, were added to the synthesised liquid crystals. The LC-nanocomposites exhibit excellent thermal conducting performance when a combination of BNNSs and Al₂O₃ nanoparticles were added to the liquid crystals. The thermal conductivity of the 4i-BN35-A15 nanocomposite was 1.7 W/m K compared to 0.3 W/m K for the pure liquid crystal compound 4i.

GRAPHICAL ABSTRACT

KEYWORDS:

• Coumarin
• biphenyl
• dimeric liquid crystals
• SmC phase
• nanoparticles
• thermal conductivity

Acknowledgments

The main author AK-T. Mohammad would like to thank Professor John West, Liquid Crystal Institute, Kent State University, USA.

Disclosure statement

No potential conflict of interest was reported by the author(s).