Il Cheol Jeon

Bulk modulus of the C60 molecule via the tight binding method

Abstract The bulk modulus for the C 60 molecule is calculated using total energy minimization via the tight binding method. The calculated bulk modulus is 717 GPa, which is about 1.6 times larger than that of bulk diamond due to the high symmetry of the C 60 molecule; a possible explanation is given. This result is compared to a simple estimation from elasticity theory. Electronic structures and vibrational frequencies are also compared to theoretical and experimental results.

Diamond-like carbon electrodes in electrochemical microgravimetry

Abstract Conducting diamond-like carbon films on quartz crystal electrodes were prepared by laser ablation of graphite. They were stable in many solvents including water, dichloromethane, and acetonitrile. Their potential window is much wider than those of the metal electrodes used usually in quartz oscillators and the electron transfer rate at the electrode surface is fast enough to perform electrochemistry. In dichloromethane with 0.1 M (n-Bu)4NClO4, DLC electrodes could scan the potential range between +2.0 and −2.0 V to record cyclic voltammetric (CV) curves of [Ru(bpy)3]3+/2+. We also showed that the DLC works satisfactorily as a useful electrode material for electrochemical microgravimetry by examining the deposition–dissolution of [Ru(bpy)3]3+ in dichloromethane solutions. It was found that the oxidized [Ru(bpy)3]3+ have two different fates, that is, some of them make deposits on the DLC electrode and the rest diffuse out of the electrode surface instead of depositing. Based on the frequency data representing the amount of deposit only and the oxidation charge data reflecting the amount of oxidized species, deposits were found to have the average composition of [Ru(bpy)3](ClO4)3 · 1.7(n-Bu)4NClO4.

Ionic surfactant-triggered renewal of the structures and properties of polyelectrolyte multilayer films.

The present study investigated the effects of ionic surfactants on polyelectrolyte multilayer (PEM) films, consisting of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), prepared using a sequential layer-by-layer (LbL) technique. The electrostatic interaction between sodium dodecyl sulfate (SDS) and the PEMs resulted in desorption of the polyelectrolytes from the PEM films, and consequently the thickness of the PEM films was altered, as confirmed by UV-vis, XPS, and AFM studies. Two critical features of this phenomenon include the porous morphology of the SDS-treated films and the simultaneous increase in the thickness of the film. Furthermore, both the rate and amount of polyelectrolytes desorbed from the PEM films could be controlled by varying the surfactant, the outermost layer, and the reaction time. The surface morphology and thickness of the PEM films could be retuned even after formation of PEMs. Thus, controlled desorption of PEs could be an effective tool for the renewal of the structures and properties of PEMs.

Polyelectrolyte complex particle-based multifunctional freestanding films containing highly loaded bimetallic particles

A facile approach to the development of multifunctional freestanding films consisting of polyelectrolytes (PEs) and polyelectrolyte complexes (nPECs) with highly embedded metal nanoparticles (NPs) was demonstrated. The composite films (nPEC/PE) containing NPs exhibited controllable properties that can be exploited by varying the type and content of NPs with high loading density. The approach described here enables the facile fabrication of conducting and transparent freestanding films with tunable optical/electrical properties, color, and large lateral dimensions with minimal effort in terms of the number of layers and ease of operation.

Properties of nitrogen-doped diamond-like-carbon films prepared by a laser ablation

Abstract We have successfully introduced nitrogen into diamond-like-carbon films by evaporating carbon and nitrogen ions simultaneously from a carbon target dipped in hexamethylenetetramine solution with a laser. Nitrogen content in the film was changed by varying the molar concentration of hexamethylenetetramine solution. This method needs no vacuum arc and provides a simple effective way of nitrogen addition. The resistivity measured as a function of nitrogen content decreases up to a certain nitrogen content and then increases at higher nitrogen content, suggesting that nitrogen act as a true dopant. Atomic force microscopy and Raman spectroscopy studies also suggest that no graphitization whatsoever occurs in the films after nitrogen addition. Although no structural change in the films was found with nitrogen addition, the emission threshold field decreased by ∼4–5 V/μm depending on nitrogen content. The nitrogen-added diamond-like-carbon film was found to have a typical threshold field of ∼10 V/μm at optimal composition.

Free-standing polymer nanoactuators, nanoshutters, and nanofilters

Our study demonstrates a facile approach for the synthesis of metal NP-embedded freestanding polyelectrolyte complexes (PECs) without sacrificial templates, which can be used as nanoactuators, nanoshutters, and nanofilters. The metal NP-PECs were prepared by mixing metal precursor-preadsorbed cation and anion PEs, using a nonstoichiometric ratio, followed by a controlled heat treatment. The metal NP-PECs showed reversible structural changes such as shrinking or swelling when they were exposed to various pH conditions. During the changes, they were also able to reversibly control the interparticle distance of the metal NPs embedded in the PECs, which has allowed the easy tuning of their catalytic and optical properties. By the reversible control of structural changes, the PECs can also be used as nanoshutters to reversibly control the flow of nanomaterials in the channels or pores. Furthermore, metal NP-embedded PECs, Au/Ag-PECs, were demonstrated to be useful as nanofilters for removing or transforming unwanted materials.

Synthesis, binding properties and electrochemistry of nickel(II) macrocyclic complexes containing crown ethers

Abstract Macrotetracyclic complexes of nickel(II) containing crown ethers as pendant arms, [Ni(B)](ClO4)2 and [Ni(C)](ClO4)2, were prepared and characterized. The binding constants of the complexes toward alkali metal ions are relatively small compared with those of free 15-crown-5 or 18-crown-6 and the reduction potentials of the [Ni(B)](ClO4)2 and [Ni(C)](ClO4)2 in the presence of alkali metal ions shift to the positive direction in the order Li+>Na+>K+ and K+>Na+>Li+, respectively.

A New Optical Film with Antismudge Function and High Durability

We describe a new surface treatment to obtain optical films for liquid crystal display (LCD) applications. The films consist of a phase-separated layer including a fluorine-containing (FC) compound and a widely used polymer resin for providing a hard coating after surface treatment of the optical film. The major features of the resulting configuration are high durability with a good hardness of above 4H and a surface that allows oily contaminants such as ink and fingerprints to be easily removed by gentle dry wiping, owing to the antismudge function of the FC compound with a low surface energy.

Creation of a voltage controllable micro-liquid crystal domain using the atomic force microscope rubbing for surface modification

We have studied the liquid crystal (LC) alignment on a modified homeotropic polymer surface using an atomic force microscopy (AFM) rubbing. The nano-rubbing by AFM shows well-defined LC alignment and the rubbed surface induces the LC to be planarly aligned. The hybrid aligned nematic LC cell as made shows dynamic stability while increasing voltage without causing disclination lines and asymmetric light transmittance in oblique viewing angles. The result indicates that the pretilt angle is generated from the homeotropic alignment layer to the initial scanning direction, and the device is useful as a light modulator or dynamic phase retarder in the micron or nano region.