Lyotropic Side‐Chain Liquid Crystalline Poly(6‐(4‐cyanobiphenyl‐4′‐yloxy) hexyl acrylate) in Ternary Mixtures of N ‐Methyl‐2‐pyrrolidone and Deep Eutectic Solvent for Thermal Energy Storage

ABSTRACT Liquid crystals today have been proposed as alternative storage materials, which are based on their ability to absorb and release energy at a constant temperature while maintaining their flow properties. In this work, lyotropic liquid crystal has been chosen as a method to explore the opportunity in thermal energy storage applications. Side‐chain liquid crystalline polymer (SCLCP) containing biphenyl mesogens was synthesized, and we present for the first time the self‐aggregation of the SCLCP in N ‐methyl‐2‐pyrrolidone (NMP) with various deep eutectic solvents (DES). The lyotropic behavior of the SCLCP in NMP/DES systems was studied using a polarized optical microscope (POM) and differential scanning calorimetry (DSC). A schlieren texture, which indicated a nematic phase, was observed at room temperature in the concentration range of 2–6 wt% as evidenced by POM. Interestingly, at higher temperatures, a thermochromic effect was displayed as they changed color because of the nanoscale shifts in the arrangement of their molecules. Combined with DSC results, an endothermic peak emerged during the second heating, which corresponded to the isotropization transition temperature ( T i ). The temperatures obtained were almost similar, ~78°C, due to the existence of one liquid crystal phase. Experimental results indicated that the incorporation of SCLCP and DES facilitated the alignment and arrangement of mesogen molecules in the lyotropic phase, which offers a potential improvement in TES application.