Junko Morikawa

The development of polymer materials with high intrinsic thermal conductivity is essential for efficient heat dissipation in next-generation electronics. In this study, we report the fabrication and characterization of liquid-crystalline (LC) polyimide nanofibers (PI-NFs) designed to achieve a highly ordered internal structure. Highly aligned LC-PI-NFs were prepared via electrospinning of a poly(amic acid) precursor containing rigid phenyl benzoate mesogens and flexible dodecyl spacers, followed by stepwise thermal imidization. To further enhance molecular alignment, uniaxial tensile drawing was applied during the imidization process. Upon thermal imidization, wide-angle X-ray scattering (WAXS) revealed a phase transition from the initial smectic (Sm) A phase to a more ordered SmF phase. Furthermore, combined WAXS and small-angle X-ray scattering (SAXS) analyses suggested that uniaxial drawing enhances the ordering of the LC structure. Microscale temperature wave analysis demonstrated a positive correlation between the internal structural order and the thermal diffusivity along the fiber axis, which reached a value of 6.6 × 10–7 m2 s–1 (corresponding to a thermal conductivity of 1.0 W m–1 K–1) for the uniaxially drawn LC-PI-NFs. These results demonstrate that synergistically integrating LC phase behavior with processing-induced strain is a promising strategy for developing high-performance, thermally conductive polymer nanostructures.

The in-plane thermal diffusivity of soft materials is critical for the development of functional thermal materials in nano/microscale integrated devices

Understanding heat transport at the graphene-polymer ( Gr -polymer) interface is the key to improve the thermal conductivity of Gr -based nanocomposites. Here, we fabricate poly (methyl methacrylate)/graphene (PMMA/ Gr ) nanolaminates and find an ultrahigh increase of the in-plane thermal conductivity (8.9 ± 0.9 W m − 1 K − 1 ) compared to net PMMA and the thermal conductivity anisotropy (approximately equal to 53) at low Gr loading (1 vol. %). The strong anisotropic thermal conduction can be attributed to the predominantly in-plane oriented Gr nanoflake and, intriguingly, the graphene-induced planar alignment of PMMA in the proximity of Gr , as revealed by polarized infrared spectroscopic (-IR) imaging, nano-FTIR and IR s-SNOM. We demonstrated the contribution of interface-induced confinement to the observed thermal property, providing deeper insights into heat transport at the Gr -polymer interface.

Next-generation power electronics require efficient heat dissipation management, and molecular design guidelines are needed to develop polymers with high thermal conductivity. Polymer materials have considerably lower thermal conductivity than metals and ceramics due to phonon scattering in the amorphous region. The spontaneous orientation of the molecular chains of liquid crystalline polymers could potentially give rise to high thermal conductivity, but the molecular design of such polymers remains largely empirical. In this study, we developed a machine learning model that predicts with more than 96% accuracy whether liquid crystalline states will form based on the chemical structure of the polymer. By exploring the inverse mapping of this model, we identified a comprehensive set of chemical structures for liquid crystalline polyimides. The polymers were then experimentally synthesized, and the results confirmed that they form liquid crystalline phases, with all polymers exhibiting calculated thermal conductivities within the range of 0.722–1.26 W m⁻¹ K⁻¹.

This study investigates water transport in a polymer electrolyte membrane (PEM) electrolyzer using operando infrared spectroscopic imaging. By testing different H2SO4 anolyte concentrations, it examines electrochemical performance, water diffusion, and membrane hydration. Higher anolyte concentrations increased standard deviations in current densities and led to water diffusion gradients revealed by infrared imaging and confirming localized water transport variations. The study highlights the need for improved water management and optimized electrolyzer design for stable and efficient PEM electrolysis in industrial applications.

Nanoscale measurements of thermophysical properties, based on detecting temperature responses to periodic heat stimulation, can be achieved using a localized heating point instead of a localized sensing point. However, the concept of determining localized thermophysical properties via nano-heating as an alternative to nano-sensing has not yet been validated. In this study, we demonstrate the measurement of thermal diffusivity within a nanoscale-confined volume using a thermal scanning probe lithography (t-SPL) system. The sharp tip of the t-SPL probe is employed to locally and periodically heat the sample, which is placed on a pre-fabricated micro-thermocouple. Using the temperature wave analysis method, the thermal diffusivity of the sample is inferred from the frequency-dependent phase shift in the temperature response of a thermocouple. This technique was applied to the microscale structure of a chemically amplified negative-tone photoresist (mr-DWL). We show that confining the heat source to a nanoscale point contact can achieve spatial resolution at the nanoscale (10–100 nm), offering an alternative approach to miniaturizing the detector sensor.

Discotic columnar liquid crystals (LCs) hold promise as thermal interface materials that allow heat to flow preferentially in the desired direction, whereas their heat transport properties remain elusive, particularly in terms of anisotropy related to their columnar alignments. Using a discotic columnar LC (TPC₄F₆) that allows for complete alignment control by applying mechanical shear, we investigated the alignment dependence of the thermal diffusivity using a dedicated setup for micro temperature wave analysis. We found that the thermal diffusivity in the direction perpendicular to the columns is larger, compared with the direction along the columns. Interestingly, this trend is opposite to that observed for a single crystal system composed of an identical aromatic core motif. This result demonstrates that the anisotropy of heat transport can change depending on the phases of materials even when they have similar compositions, providing insights into the design of organic materials for thermal management.

Anisotropy plays a critical role in governing the mechanical, thermal, electrical, magnetic, and optical properties of materials, influencing their behavior across diverse applications. Probing and quantifying this directional dependence is crucial for advancing materials science and biomedical research, as it provides a deeper understanding of structural orientations at the molecular level, encompassing both scientific and industrial benefits. This study introduces the "4+ Angle Polarization" widget, an innovative extension to the open-source Quasar platform (https://quasar.codes/), tailored for advanced multiple-angle polarization analysis. This toolbox enables precise molecular orientation analysis of complex microspectroscopic datasets through a streamlined workflow. Using polarized Fourier transform infrared (p-FTIR) spectroscopy, we demonstrate its versatility across various sample types, including polylactic acid (PLA) organic crystals, murine cortical bone, and human osteons. By overcoming the limitations of traditional two-angle methods, the widget significantly enhances the accuracy of structural and orientational analysis. This novel analytical tool expands the potential of multiple-angle p-FTIR techniques into advanced characterization of structural anisotropy in heterogeneous systems, providing transformative insights for materials characterization, biomedical imaging and beyond.