Hyeonuk Yeo

A facile method for transparent carbon nanosheets heater based on polyimide

In this work, a novel film heater in nanometer-scale thickness based on catalyst-free and transfer-free carbon nanosheets (CNSs) with properties similar to graphene is fabricated. Here, poly(amic acid) (PAA), which is composed of several aromatic hydrocarbon rings, is used as the carbon precursor of CNS films. Altering the polymer concentration easily controls the morphological, optical, and electrical properties of the CNS films obtained by carbonization of PAA thin films. The CNS films with different thicknesses of 7.53–28.40 nm are simply prepared through spin-coating on a quartz substrate and post heat-treatment. Finally, their direct use as transparent film heaters is deeply investigated by considering electrical conductivity, temperature response rapidity, achievable maximum temperature, and electric power efficiency. For instance, an electrically conductive and optically transparent CNS film with 28.40 nm thickness exhibits excellent electric heating performance achieving well-defined steady-state maximum temperatures of 24–333 °C at low input electric power per unit film area of 0.027–1.005 W cm−2 in a relatively short time of ∼100 s.

Synthesis of benzo[h]quinoline-based neutral pentacoordinate organosilicon complexes.

Reactions of 10-benzo[h]quinolyllithium with a series of organosilanes led to the formation of neutral pentacoordinate complexes. The diethynyl-substituted complex was able to be converted to di(arylethynyl)-substituted ones by the Sonogashira-Hagihara coupling reaction. Electronegative substituents shortened N-Si distances and enhanced fluorescence intensity from the complexes.

Chemical method for improving both the electrical conductivity and mechanical properties of carbon nanotube yarn via intramolecular cross-dehydrogenative coupling.

Chemical post-treatment of the carbon nanotube fiber (CNTF) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G band to the D band (IG/ID ratio) of CNT fiber increased from 2.3 to 4.6 after ICDC reaction. From the XPS measurements, the AC═C/AC-C ratio of the CNT fiber increased from 3.6 to 4.8. It is of keen interest that both the electrical conductivity and tensile strength of CNT yarn improved to 3.5 × 10(3) S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn.

Synthesis and tuning of optical properties of conjugated polymers involving benzo[h]quinoline-based neutral pentacoordinate organosilicon complexes in the main chain

We present the synthesis and optical properties of a series of alternating polymers containing pentacoordinate silicon complexes in the main chain. By employing the benzo[h]quinoline ligand, the pentacoordinate silicon complexes were obtained. The polymers were prepared via the Sonogashira–Hagihara coupling reaction. From the series of measurements for optical properties of the synthesized polymers, new absorption bands and bathochromic shifts in emission spectra were observed. These data suggest that intramolecular charge transfer could occur after the excitation because of the elongation of π-conjugation via the polymer main chains. The modulation of the optical properties of the conjugated polymers involving the pentacoordinate silicon was accomplished.

Construction and properties of a light-harvesting antenna system for phosphorescent materials based on oligofluorene-tethered Pt–porphyrins

Tetramerous molecular assemblies composed of four oligofluorenes as a light-harvesting antenna (LHA) and a Pt–porphyrin core as a phosphorescent chromophore were designed and synthesized for obtaining efficient phosphorescent materials. The resulting molecules showed good solubility in common organic solvents and high film-formability. From the series of optical measurements, it was shown that bright phosphorescence was observed from the LHA molecules. Efficient energy transfer through the cardo structure was confirmed from the oligofluorene units to the Pt–porphyrin core. Additionally, it was shown that aggregation-caused quenching (ACQ) and oxygen-deactivation of phosphorescence can be inhibited in the film state because of steric hinderance of bulky rings on the cardo structure. Finally, film materials with oxygen-resistant solid-state phosphorescence were obtained. Our material design is feasible not only for constructing highly-emissive solid-state phosphorescent materials but also for enhancing environment resistance to emissive materials by a unique structural unit.

Synthesis and preparation of alkyl-functionalized graphene oxide/polyimide nanocomposites

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Preparation of porous carbon materials by using coagulated polyamic acid precursor

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Thermomechanical Behavior of Polymer Composites Based on Edge-Selectively Functionalized Graphene Nanosheets

In this study, we demonstrate an effective approach based on a simple processing method to improve the thermomechanical properties of graphene polymer composites (GPCs). Edge-selectively functionalized graphene (EFG) was successfully obtained through simple ball milling of natural graphite in the presence of dry ice, which acted as the source of carboxyl functional groups that were attached to the peripheral basal plane of graphene. The resultant EFG is highly dispersible in various organic solvents and contributes to improving their physical properties because of its unique characteristics. Pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) were used as monomers for constructing the polyimide (PI) backbone, after which PI/EFG composites were prepared by in situ polymerization. A stepwise thermal imidization method was used to prepare the PI films for comparison purposes. The PI/EFG composite films were found to exhibit reinforced thermal and thermo-mechanical properties compared to neat PI owing to the interaction between the EFG and PI matrix.

Highly thermal conductive resins formed from wide-temperature-range eutectic mixtures of liquid crystalline epoxies bearing diglycidyl moieties at the side positions

To develop advanced thermally conductive epoxy resins with liquid crystallinity, three novel liquid crystalline epoxies (LCEs) were synthesized via the substitution of phenylcyclohexyl (PCH) mesogenic moieties into the 2,5 positions of diglycidyl terephthalate. Mesomorphic properties of LCEs were evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). All LCEs exhibited an enantiotropic smectic phase on heating and cooling. Remarkably, the smectic phase with a wide temperature range of 98–145 °C was observed for the eutectic mixtures of a family of stable smectic LCEs. The selection of optimum curing agents, compositions of LCEs and curing agents, and curing conditions were determined based on physical, chemical, and thermal properties of LCEs and curing agents. The thermally cured LCEs at the LC phase exhibited a high thermal conductivity of 0.4 W m−1 K−1.

Synthesis and Characterization of New Diamines Containing Rigid Aromatic Ester Units as Curing Agent for High Performance Epoxy Resin

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