Jongmin Park

Encoding molecules as strings has unlocked language models for property prediction and inverse design, but the choice of molecular representation plays a critical role in model performance. Atom-level tokenization such as SMILES employ complex syntax and require models to reconstruct substructure-level chemical meaning from character-level patterns. These limitations are amplified for complex molecular systems with small datasets, such as polymers. We introduce CI-LM (Chemically Informed Language Model), built on HAPPY (Hierarchically Abstracted rePeat unit of PolYmer), a representation that replaces SMILES grammar with chemically meaningful subgroups. Critically, each subgroup is augmented with physicochemical descriptors that inform both token embeddings and attention computations, making chemical priors available before training begins. For property prediction, CI-LM improves accuracy and inference efficiency over SMILES baselines while providing subgroup-level interpretation. For inverse design, it enables scaffold-constrained generation and multi-objective optimization of negatively correlated properties in sparse chemical space, where SMILES-based approaches fail.

Dip-coating is a simple yet versatile deposition method inherently compatible with complex, non-flat surfaces. Unlike conventional horizontal coatings, its vertical withdrawal configuration demands precise control over viscosity, surface tension, evaporation, and gravity to achieve uniform thin films. However, the performance of dip-coated perovskite solar cells (PSCs) has remained limited because commonly used volatile-solvent-dominated precursor inks provide inadequate morphological control. Also, conventional dip-coating strategies for rheological control are unsuitable for PSCs, as polymeric binders or high precursor concentrations can impair crystallization and charge transport. Here, by reversing the conventional DMF-dominant formulation, we identify an NMP-dominant DMF:NMP (= 7:93 (vol%/vol%)) solvent system that enables uniform, pinhole-free perovskite films via dip-coating. The resulting devices exhibit power conversion efficiencies exceeding 25%, representing the highest reported performance for dip-coated PSCs. Moreover, the ink enables conformal coating on textured, curved, and three-dimensionally complex surfaces. This work establishes an ink-design strategy for high-performance dip-coated PSCs, opening a practical pathway toward perovskite photovoltaics on nonplanar and structurally diverse substrates.

Lightweight, flexible, and thermally robust neutron-shielding materials are essential for nuclear, aerospace, space, and defense applications, yet conventional polymer composites struggle to balance filler loading with flexibility, thermal stability, and processability. Here, we report an aqueous in-situ polymerization strategy for fabricating boron nitride nanotube (BNNT)-incorporated polyimide (PI) composite films (PIBT) with BNNT loadings up to 90 wt%. BNNTs are incorporated during water-borne poly(amic acid) salt (W-PAAS) precursor formation, yielding free-standing PI–BNNT films without post-synthetic functionalization or toxic aprotic solvents. Composition-dependent analysis shows that shielding efficiency depends not on nominal BNNT content alone, but on the balance among boron-site density, absorber distribution, and matrix continuity. The optimized PIBT-60 film achieves a linear neutron attenuation coefficient of 1.67 mm⁻¹, a mass attenuation coefficient of 9.23 cm² g⁻¹, an in-plane thermal conductivity of 8.23 W m⁻¹ K⁻¹, a 2.5 mm minimum bending radius, and a 5% weight-loss decomposition temperature above 600 °C in a sub-100 μm film. Neutron transport simulations of a lunar extravehicular mobility unit show that PIBT-60 reduces low-energy neutron flux within a realistic multilayer protective structure. This work establishes aqueous in-situ processing as a route for multifunctional PI-based composite films integrating neutron shielding, heat spreading, flexibility, and thermal endurance for harsh-environment applications.

Fluorene-containing polyimides with pendant hydroxyl groups were synthesized via azeotropic imidization from BPADA, mTB, and APFD in varying feed ratios. Post-polymerization cross-linking with terephthaloyl chloride (TPC) generates covalent junctions between polymer chains, disrupting dense packing and arresting expanded inter-chain free space. Wide-angle X-ray Scattering (WAXS) analysis confirmed that the formation of cross-linked networks increased free volume in the polymer matrix, leading to a reduction in dielectric constant (D_k) and dissipation factor (D_f). The CBMAD73(1.0) film exhibited the advanced low dielectric properties with D_k = 2.66 and D_f = 0.0056 at 10 GHz, compared to 3.13 and 0.0246 at 10 GHz for the polymeric precursor, BMAD73. Thermal analysis demonstrated that the cross-linked polymer network retained thermal stability, which is comparable to that of the neat polyimide precursor, demonstrating structural integrity of the cross-linked network. These results highlight post-polymerization cross-linking as an effective approach for modulating nanoscale free volume to achieve low dielectric performances while maintaining thermal stability required for high-frequency electronic applications.

Wireless powering of implantable medical devices (IMDs) using triboelectric nanogenerators (TENGs) has gained attention as a sustainable and battery-free energy strategy. Ultrasound-driven TENGs (US-TENGs) offer favorable biocompatibility and deep tissue accessibility, but their practical application remains limited by unstable acoustic vibration, filler aggregation at low contents, and complex electrode integration. Here, we report a porous polyimide composite-based TENG (PPC-TENG) designed to overcome these limitations through material and structural innovations. The triboelectric layer is fabricated via a Pickering emulsion templating approach using a water-borne poly(amic acid) salt (W-PAAS) and high-permittivity CaCu₃Ti₄O₁₂ (CCTO) nanoparticles, enabling homogeneous dispersion up to 10 wt % without aggregation. The resulting porous architecture concentrates mechanical deformation at branch-like pore supports, promoting uniform vibration and enhancing charge generation under acoustic actuation. A laser-induced graphene (LIG) electrode is directly patterned on the porous surface, enabling a double-electrode configuration through a simplified, metal-free process. The PPC-TENG exhibits high electrical output, stable capacitor and battery charging performance, and confirmed biocompatibility in both in vitro and in vivo tests. This work presents a scalable and structurally adaptive triboelectric platform for wirelessly powered biomedical electronics.

Thin-film transistors offer excellent and uniform electrical properties over large areas, making them a promising option for various future electronic devices. Polyimide dielectrics are already widely used in various electronic devices because of their exceptional dielectric properties, thermal stability, and desirable mechanical flexibility, which make them suitable for harsh environments. However, the current research on polyimide dielectric materials has certain limitations, such as the use of toxic solvents, high-temperature processes, and deficient coating properties. Herein, we introduce an aromatic polyimide dielectric, which exhibits excellent electrical properties even when processed at a low temperature of 250 °C using environmentally friendly water-based "one-step" polymerization. Despite its thin thickness of -1. Furthermore, we successfully achieved a large-area coating of uniform dielectric layers with no pinholes using only water as a solvent and a simple solution process without any additional processing steps. These results demonstrate that the water-borne polyimide gated indium-gallium-zinc oxide transistor exhibits excellent and stable device performance. Moreover, we used the transistor to successfully demonstrate various logic gates (NOT, NAND, and NOR). Overall, this study provides guidelines for the eco-friendly and sustainable use of water-borne polyimide dielectric materials with high electrical performance and large-processing window advantages.