Seunghan Shin

Synthesis of carbohydrate biomass-based furanic compounds bearing epoxide end group(s) and evaluation of their feasibility as adhesives

Current issues of energy and environment prompt us to replace fossil-based resources with renewable and sustainable ones. In this regard, carbohydrate biomass photosynthesized from atmospheric carbon dioxide attracts much attention due to its abundance and availability. Recently, furanic compounds that can be derived from carbohydrate biomass are highlighted as promising substitutes for aromatic compounds that are totally dependent on petroleum reforming processes. In this article, we report on several carbohydrate biomass-based furanic compounds as alternatives to petroleum-based adhesives. Furanic compounds bearing epoxide end group(s) were synthesized from renewable and sustainable carbohydrate biomass-based compounds (>70% yields). Another bis-epoxy furanic compound with a mimetic structure of bisphenol A (BPA) was also synthesized from xylose-derived 2-furan carboxylic acid and acetone (39% overall yield). In particular, epoxy groups were efficiently introduced to the hydroxymethyl functionality attached by furanic cores under the bi-phasic solvent system using phase transfer catalysis. Cationic photo-curing kinetic profiles of synthetic compounds were investigated in terms of heat flow integrals using photo-DSC. It was found that their halftime values (t 1/2), representing curing rates, ranged from 0.54 to 1.15 min when irradiated with 40 mW/cm2 UV light. When synthetic furanic compounds functionalized by epoxide group(s) were used for bonding polycarbonate by cationic photo-curing, we noted that tensile-shear strength of PC joints bonded with biomass-based furan mono-epoxide having furan ring was greater (4.7 MPa) than that of joints bonded with petrochemical-based phenyl glycidyl ether having phenyl ring (2.6 MPa). When bonded with di-epoxide functionalized furan di-epoxide, tensile-shear strength of PC joint was 3.5 MPa after photo-curing for 3 min at 40 °C. However, bis-furan di-epoxide (bFdE), the mimetic compound of BPA showed lower tensile-shear strength (approximately 1 MPa) due to structural features of bFdE, such as rigidity and hydrophobic property.

Phase transition control of nanostructured TiO2 powders with additions of various metal chlorides

Formation behavior and photo-oxidation abilities of nanostructured TiO2 powders were investigated through a direct crystallization from aqueous TiOCl2 solutions containing various metal chlorides at 100??C. The obtained TiO2 powders without any additives and those with Ni2+, Fe3+ and Nb5+ ions added, which have a similar positive ionic radius to Ti4+, were mainly crystallized with rutile phase, whereas those with Al3+ and Zr4+ ions added, which have a quite different positive ionic radius, were mainly crystallized with anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles, corresponding to rutile and anatase phases, respectively. From these results, it seems that the positive ionic radius of the additives would affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni-added powder, which consisted mainly of rutile phase with a small amount of anatase phase, showed excellent photocatalytic ability in decomposition of 4-chlorophenol.

Tuning Helical Twisting Power of Isosorbide-Based Chiral Dopants by Chemical Modifications

Isosorbide-based chiral dopants (ICD) with various substituent groups were newly synthesized to control their helical twisting powers (HTP). Phase transition behaviors of ICD molecules were first investigated by combined techniques of differential scanning calorimetry, wide-angle X-ray diffraction, and cross-polarized optical microscopy. ICD with n-hexyloxy end groups formed the multiple ordered phases, and those with methoxy or acetoxy end groups exhibited a simple crystal-to-isotropic transition. Energy-minimized chemical conformations of ICD molecules revealed that all the ICDs had twisted conformations and that the extension of the benzoyl ester moiety induced a higher twisted conformation. By varying substitution groups, HTPs of ICDs were controlled from 26.6 to 80.2 μm−1. Particularly, ICD with an acetoxy end group (ICD-2) showed the largest HTP. It was also realized that by controlling the content of ICD-2 from 3.0 to 4.5 mol%, the helical pitch length of cholesteric LC mixture was adjusted to reflect a specific visible light.

A macroscopically oriented lyotropic chromonic liquid crystalline nanofiber mat embedding self-assembled Sunset-Yellow FCF nanocolumns

A macroscopically oriented anisotropic nanofiber mat embedding self-assembled Sunset-Yellow FCF nanocolumns was fabricated by the electrospinning technique. From the 2D WAXD and polarized FTIR results, it was realized that the nanocolumns were aligned parallel to the long axis of the nanofiber.

A biobased photocurable binder for composites with transparency and thermal stability from biomass-derived isosorbide

A biobased photocurable binder was synthesized from isosorbide in a high yield (91%) and used as a binder for transparent glass fabric composites. The photocurable isosorbide binder showed a lower refractive index (n = 1.489) than that of glass (n = 1.560) and low viscosity (48.6 cP at 25 °C) owing to the wedge-shaped fused ring structure of the isosorbide moiety. Transparent glass fabric composites were prepared by refractive index matching using a cardo-type fluorene based binder (n = 1.583) as a co-binder. A glass fabric composite photocured with equal wt% of the cardo- and isosorbide-based binder showed 85% of transmittance at 550 nm by UV-visible spectroscopy. It also showed a considerably good coefficient of thermal expansion (α1 = 16.3 ppm K−1) and glass transition temperature (142 °C by DMA). As the wt% of the isosorbide-based binder increased, the network structure of the binder mixture became tight to give a higher glass transition temperature but the composites transparency was decreased.

Structural and Morphological Evolution for Water-resistant Organic Thermoelectrics

We systematically investigated the effect of 2,5-bis(2-hydroxy-3-methacryloyloxypropoxy)-1,4:3,6-dianhydro-sorbitol (Iso-GMA) with different concentrations on the structural and morphological evolution of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) containing a fixed volume of dimethyl sulfoxide (DMSO) to realize water-resistant organic thermoelectric devices. As an additive, Iso-GMA is a hydrophilic and crosslinking agent that can interact with PEDOT and PSS chains by hydrogen bonding and/or dipole-dipole- or dipole-charge-interaction. The Seebeck coefficient and power factor in the film incorporating 3.0 vol% DMSO and 0.8 vol% Iso-GMA were respectively 1.82 × 102 and 1.53 × 105% higher than those of the pristine PEDOT:PSS film without additives (DMSO and Iso-GMA). These results can be attributed to the self-assembled and crosslinked fibril networks with optimized phase separation, where the film has densely-packed PEDOT and highly lamellar-stacked PSS. Also, the reduced charge carrier concentration from the structural characteristics originated in the higher thermoelectric properties. We introduced the schematic illustration to understand the chemical bonding among the components and the morphological evolution according to the Iso-GMA concentration. The increased mechanical strength by the interchain stacking degree of PEDOT and the crosslinking of Iso-GMA facilitate the film remained in a water bath for 0.5 h without physical degradation, and sustain the thermoelectric properties during 12 h in humid conditons.

Preparation of Nanostructured TiO2 Powders with Additions of Various Metal–Chlorides for Efficient Photocatalyst

Preparation of nanostructured TiO2 powders for efficient photocatalyst was investigated through a direct crystallization from aqueous TiOCl2 solutions containing various metal–chlorides. The TiO2 powders without any additives and those added with Ni2+, Fe3+ and Nb5+ions, respectively, which has a similar cationic radius to Ti4+, were mainly crystallized to rutile phase, whereas those added with Al3+ and Zr4+ ions, which have a quite different positive ionic radius, were mainly crystallized to anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles corresponding to rutile and anatase phases, respectively. From these results, it seems that the cationic radius of the additives could affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni2+ doped powder, showing mainly rutile phase, had excellent photocatalytic ability in decomposition of 4-chlorophenol.

A Novel Wholly Aromatic Liquid Crystalline Epoxy Monomer Based on 2,7-Naphthalene Mesogen: Synthesis and Curing with Aromatic Diamine

AbstractA novel all aromatic 2,7-naphthalene-based liquid crystalline epoxy (LCE) was synthesized successfully in this study. The thermal transition of the synthesized LCE was characterized by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). The characterization showed that the LCE had a low melting temperature of 65 °C and was in a nematic state in temperature range of 65–75 °C. The curing reaction between LCE and 4,4′-diaminodiphenylsulfone (DDS) was investigated, using 2-methylimidazole (2MI) as the reaction catalyst. Upon the addition of 1 phr of 2MI, the curing temperature was dramatically decreased from 227 to 128 °C, which is 99 °C lower than that of a reaction without the use of a catalyst system.

Bio-based chiral dopants having an isohexide skeleton for cholesteric liquid crystal materials

Chiral dopants were synthesized from bio-based epimeric isohexides (glucose-derived isosorbide and mannose-derived isomannide) and their phase transition behaviors and abilities for developing cholesteric liquid crystal (CLC) films were examined with a consideration of the core structure. In spite of lower reactivity of the endo hydroxy group of isomannide caused by the steric hindrance and intermolecular hydrogen bonding, final synthetic yields of chiral dopants bearing an isomannide core (64.5% for IH-2 and 65.0% for IH-4) did not show conspicuous difference compared with chiral dopants bearing isosorbide (68.4% for IH-1 and 74.0% for IH-3). On the other hand, in phase transition behaviors, chiral dopants bearing an isomannide core showed lower crystalline and melting temperatures than IH-1, IH-3 despite of the same substituents. The helical twisting power (HTP) of chiral dopants bearing isosorbide (IH-1 and IH-3) was higher than that of chiral dopants bearing isomannide (IH-2 and IH-4). The calculated HTPs of IH-1 and IH-3 were 26.6 and 42.1 μm−1, respectively. In the case of IH-3, the helical pitch length of CLC could be adjusted to reflect visible light by controlling its amount and showed best performance in the range 5.0 to 7.0 mol%. In contrast to IH-1 and IH-3, it was found that IH-2 and IH-4 could not induce CLC films that reflect visible light.

Preparation of Electronic Ink Using TiO2 Particles Dispersed in Low Dielectric Solvent

An electrophoretic display using Ti0 2 particles is the most promising candidate because it offers various advantages such as ink-on-paper appearance, good contrast ratio, wide viewing angle, image stability in the off-state and extremely low power consumption. The core technology of electrophoretic display is dispersion controlling of TiO 2 nano particles in nonaqueous solution. To prepare an ink for electronic paper using TiO 2 nano particles, cyclohexane with low dielectric constant and transparency, polyethylene for producing polymer coating layer which reduces apparent density of Ti0 2 , and TiO 2 nano powders were intermixed using planetary-mill. The zeta-potential value of Ti0 2 particles in cyclohexane was measured about -40 mV, but was measured over -110 mV by dispersant attached to polyethylene-coated TiO 2 surface. Prepared electronic ink was filled in cross patterned micro-wall with 200 μm in width and 40 μm in height on ITO glass designed by photolithography. The response time of electronic paper evaluated by mobility of TiO 2 particle between micro-walls was measured 0.067sec, but the drift velocity from reflectance wave form during reverse turn of electronic ink was measured 0.07cm/sec.