Myong-Hoon Lee

Electrochemical properties of polyaniline doped with poly(styrenesulfonic acid)

Abstract Polyaniline was electrochemically synthesized in aqueous 0.2 N poly(styrenesulfonic acid) solution. The electrochemical properties, such as redox kinetics with respect to the pH of the electrolytic medium and the effect of film thickness of polyaniline doped with poly(styrenesulfonic acid), were investigated by cyclic voltammetry and coulometry. Polyaniline doped with poly(styrenesulfonic acid) showed a reversible redox reaction and the rate of redox reaction was faster than that of polyaniline doped with inorganic acid even at relatively high pH (pH ∼ 4). Also, the rate of redox reaction was not affected by the thickness of the film. From cyclovoltammetric and coulometric results it was concluded that these desirable electrochemical properties are due to the ionic conductivity and proton transfer reaction of poly(styrenesulfonic acid)-doped polyaniline film.

Three-dimensional actuators transformed from the programmed two-dimensional structures via bending, twisting and folding mechanisms

Combining the physical principle of actuators with the basic concept of photonic crystals, colour-tunable three-dimensional (3D) photonic actuators were successfully fabricated. By controlling the d-spacings and the refractive index contrasts of the self-assembled 3D colloidal photonic crystals, colours of the photonic actuators were tuned. Various shapes of these 3D actuating objects were constructed by transforming the programmed 2D structures via bending, twisting and folding mechanisms. These 2D structures were first programmed by breaking the symmetry. The selective swellings were then applied as driving forces to control the shapes and colours of the photonic actuators. Scroll photonic actuators had been first demonstrated by bending the traditional 2D cantilever structure (K.-U. Jeong, et al., J.Mater.Chem., 2009, 19, 1956). By breaking the symmetry of a cantilever structure perpendicular to its long axis, polypeptide-/DNA-like 3D helical photonic actuators were obtained from the programmed 2D structure via twisting processes. Both left- and right-handed scrolls and helices with various colours can be achieved by changing the polarity of solvents. Different types of 3D actuators, such as cube, pyramid and phlat ball, were also demonstrated via the folding mechanism. The reversible 3D photonic actuators transformed from the programmed 2D structures via the bending, twisting and folding mechanisms may be applied in the field of mechanical actuators, and optoelectronic and bio-mimetic devices.

Redox Cyclability of a Self‐Doped Polyaniline

Poly(4-anilino-1-butanesulfonic acid) sodium salt was synthesized from the electrochemical oxidation of 4-anilino-1-butanesulfonic acid sodium salt, which was readily obtained from aniline and 1,4-butane sultone. The resulting water-soluble polymer has shown much higher redox cyclability than unsubstituted polyaniline, which was demonstrated by an in situ spectroelectrochemical and a cyclic voltammetric study

All solid-state electrochromic window based on poly(aniline N-butylsulfonate)s

Abstract All solid electrochromic windows were assembled by using an anodically coloring poly(aniline N-butylsulfonate) ion conducting polymer electrolyte, and a cathodically coloring tungsten trioxide. Ion conducting polymers were prepared via photo cross-linking reactions of poly(ethylene glycol)-modified methacrylates with tri(propylene glycol) diacrylate in the presence of a photo initiator and LiClO 4 . Cyclic life and the color contrast of the all solid state window were enhanced by the introduction of styrene and butylmethacrylate, and H + -conducting Nafion into the electrolyte. Lifetime tests show that the electrochromic window could support more than 2 × 10 3 cycles, of 60 sec duration.

Deposition of cubic SiC films on silicon using dimethylisopropylsilane

We have grown cubic SiC films on the Si(100) and Si(111) substrates in the temperature range of 750–970 °C by low pressure organometallic chemical vapor deposition (LP‐OMCVD) using dimethylisopropylsilane (CH3)2CHSiH(CH3)2 as a single molecular precursor. On a carbonized Si(100) substrate, a polycrystalline cubic SiC film was obtained at 960 °C. Cubic‐type SiC films were also grown on uncarbonized Si(100) surfaces at 850 °C. At lower temperatures, amorphous SiC films were formed. These growth temperatures are much lower than those reported previously by others. On an uncarbonized Si(111) substrate, however, strongly oriented growth of cubic SiC film in the [111] direction was observed at the growth temperature of 970 °C.

Low-loss and thermally stable TE-mode selective polymer waveguide using photosensitive fluorinated polyimide

A low-loss, thermally stable TE-mode selective optical waveguide was fabricated using a photosensitive fluorinated polyimide. The polymer undergoes photocrosslinking under UV exposure, thus changing its refractive index. The photocrosslinking-induced refractive index change was utilized to form channel waveguides. The propagation losses of the photosensitive fluorinated polyimide waveguides were less than 0.3 and 0.5 dB/cm for TE polarization at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The measured polarization extinction ratio was higher than 29 and 28 dB at wavelengths of 1.3 and 1.55 /spl mu/m, respectively. The refractive index of fluorinated polyimide film remains almost constant after being stored at 150/spl deg/C for 600 min.

Photochromic 3-Dimensional Actuator Based on an Uncrosslinked Liquid Crystal Elastomer

A chemically programmed photochromic liquid crystal (LC) polymer was newly synthesized and used to fabricate an actuator exhibiting reversible photo-activated bending behavior at ambient temperature. Due to the lack of chemical crosslinking in this photochromic LC elastomer, it was possible to fabricate an actuator in the form of fiber or film by melt or solution processing, respectively. The three-dimensional (3D) bending of the film actuator can be precisely controlled in various directions by polarized ultraviolet (UV) light. The novel photochromic LC elastomer, exhibiting reversible photomechanical bending with controlled directions at room temperature, is beneficial for the realization of wireless remote-controlled 3D actuators.

Dielectrophoresis force driven dynamics of carbon nanotubes in liquid crystal medium

This work reports the translation motion of carbon nanotubes (CNTs) dispersed in nematic liquid crystal (NLC) under an ac electric field. This effect was studied for homogeneously and vertically aligned NLC cells driven by in-plane field and vertical electric field, respectively. Long axis of the CNTs is aligned along the liquid crystal director, and above the critical field, the director of the NLC is distorted due to translation motion of CNTs in NLC. The amplitude of this translation motion decreases with increasing frequency, whereas the critical field increases with increasing frequency. We present the mechanism of translation motion of CNTs and model this observed phenomenon based on dielectrophoretic force.

In situ homeotropic alignment of nematic liquid crystals based on photoisomerization of azo-dye, physical adsorption of aggregates, and consequent topographical modification.

In situ homeotropic alignment is achieved by photochromic trans- to cis-isomerization of an azo-dye doped in a nematic host. The augmented dipole moment of the cis-isomer formed under UV-irradiation expedites molecular assembly into crystalline aggregates. Subsequent deposition of the aggregates creates a roughened surface and induces an anchoring transition from the initial planar to a homeotropic alignment of the LCs.

Colour-tunable spiral photonic actuators

Combining the multi-faceted environmental responsiveness of polymers with photonically active structures, we developed spiral photonic actuators which can reversibly change both shape and colour in response to the chemical environment.