Characterization of Size-Dependent Thermal Properties of Liquid Crystal Elastomer Nanofibers

The development of materials with high thermal conductivity and high latent heat offers significant advantages for thermal interface materials (TIMs), ensuring efficient heat transfer and effective thermal regulation in high-performance electronics and other thermally sensitive applications. Soft materials, due to their flexibility and conformability, further enhance these benefits by improving contact with surfaces and reducing thermal resistance. Liquid crystal elastomers (LCEs) are particularly promising candidates for TIM applications as they are soft and exhibit phase change behavior. As polymers, LCEs typically have low thermal conductivity; however, we have overcome this limitation by enhancing the alignment of liquid crystal mesogens through hydrodynamic alignment. To characterize the thermal properties of these aligned LCE fibers, we utilized a custom-built sensitive suspended thermometry platform capable of simultaneous thermal conductivity and specific heat measurements. Using a low-frequency alternating current heating method, we measured thermal conductivity, while high-frequency modulation techniques were employed to determine specific heat. Accurate specific heat measurements require fibers of optimal length: long enough to ensure good fitting sensitivity but not so long that thermal conductance decreases excessively, and radiation loss becomes dominant. Our observations indicate a significant increase in thermal conductivity, measured at 1.44 ± 0.32 W/m-K, attributed to the enhanced alignment of polymer chains in the LCE fibers with diameters in the sub-100 nm range. Additionally, we detected notable energy changes driven by the latent heat during the phase change. These findings underscore the effectiveness of our fabrication method and the superior thermal properties of LCEs as TIMs.