Daewon Sohn

Coating of multiwalled carbon nanotubes with polymer nanospheres through microemulsion polymerization

We report a simple and noncovalent method for coating multiwalled carbon nanotubes (MWCNTs) with polyaniline (PANI) nanospheres using a microemulsion polymerization method. In this method, aniline polymerization is performed with MWCNTs in the presence of sodium dodecyl sulfate (SDS), which serves as both a surfactant and a dopant. Morphological, structural, thermal, and electrical properties of MWCNT-PANI nanocomposites were analyzed. The TEM results of the nanocomposites prepared with surfactant reveal that 30-50-nm-diameter PANI nanospheres were coated on the surface of the MWCNTs. Composites prepared without surfactant were found to be in core-sheath-type cable structures. The conductivities of the nanocomposites synthesized through microemulsion polymerization were found to be one order of magnitude higher than both the conductivities of pure PANI and the composites prepared via in situ chemical polymerization without an assisting SDS surfactant. The mechanism for the formation of nanostructured composites is presented.

Transparent polymer nanohybrid prepared by in situ synthesis of aluminosilicate nanofibers in poly(vinyl alcohol) solution

Polymer nanohybrid materials that consist of poly(vinyl alcohol)(PVA) and aluminosilicate nanofiber imogolite were prepared by effective dispersion of aluminosilicate nanofiber in a polymer matrix by an synthetic method. The as-synthesized imogolite-PVA hybrid was characterized by infrared spectroscopy, wide angle X-ray diffraction and atomic force microscopic observations. The imogolite-PVA hybrid film was highly transparent compared with imogolite-PVA blend film, which was prepared by a solution blend of the freeze-dried imogolite powder with PVA. In addition, compared with PVA film, the hybrid films showed an increase in the elastic modulus and heat distortion temperature. These results indicate that synthesis of imogolite in PVA solution successfully formed the polymer nanohybrid with finely-dispersed nanofillers.

Preparation of silver nanoparticles in hexagonal phase formed by nonionic Triton X-100 surfactant

Abstract Silver nanoparticles were prepared by reducing silver ions in the hexagonal phase formed by Triton X-100 in aqueous solution. Triton X-100 molecules have been used to form the hexagonal phase in aqueous solution as well as to reduce the silver ions into silver atoms. The hexagonal phase hindered the growth and aggregation of particles. The microstructure of the hexagonal phase was investigated by polarizing microscopy, 2 H NMR spectroscopy and small-angle X-ray diffraction. At the initial stage of the reaction, silver particles prepared in the hexagonal phase exhibited a size of 1–7 nm. As the reaction proceeded, particles grew up to about 30 nm as determined by transmission electron microscopy (TEM). The formation rate of silver particles was investigated by UV–Visible spectroscopy. It was found that the reaction temperature was an important factor for the rate of particle formation. With TEM, it was confirmed that surfactant aggregates, which have flexible structures, could not absolutely prevent particles from growing and aggregating. But, the results of polarizing microscopy, 2 H NMR spectroscopy and X-ray diffraction exhibited that the growth of particles could not cause a deformation of the original structure (hexagonal phase), which was employed as the reaction medium.

High thermal stability and high tensile strength terpolyester nanofibers containing biobased monomer: fabrication and characterization

This research fabricated novel nanofibers with a terpolyester of isosorbide, ethylene glycol, 1,4-cyclohexane dimethanol, and terephthalic acid (PEICT) using electrospinning and characterized their properties. The nanofibers have higher glass transition temperature (Tg) than other polyester-type polymers, and a smaller diameter nanofiber has higher Tg than a larger diameter nanofiber. This is due to the orientation of polymer chains inside nanofibers, which was verified by DSC and polarized ATR-FTIR. The morphology and diameter of the nanofibers affected by concentration of PEICT solution were studied by SEM. It demonstrated smooth and well-formed nanofibers, and showed an increase of the diameter with increasing concentration. In addition, the tensile property, which was confirmed by UTM, was enhanced with increasing diameter because molecular orientation existed in finer nanofibers. They show a better tensile property than general biobased nanofibers such as silk, chitosan, and gelatin. Finally, fabrication of PEICT nanofibers was optimized and characterized. They can be utilized in various industrial applications such as tissue engineering, wound dressings, and health care devices.

Graphene oxide/poly(acrylic acid) hydrogel by γ-ray pre-irradiation on graphene oxide surface

AbstractGraphene oxide/poly(acrylic acid) (GO/PAA) hybrid hydrogel was prepared using a γ-ray pre-irradiation technique. The functional groups in graphene oxide were modified to peroxide in an O2 environment with γ-ray radiation. Radical species from the thermal decomposition of peroxides initiated radical polymerization of the acrylic acid monomers. Modified GO and GO/PAA hydrogels were investigated using scanning electron microscopy and Fourier transform infrared (FTIR), Raman, and electron spin resonance spectroscopy. The thermal, mechanical, and swelling properties of GO/PAA hydrogel were studied by a tensile stress-strain curve and thermal gravimetric analysis. A genuine binary hybrid hydrogel of graphene oxide and PAA was obtained from a simple synthetic procedure based on γ-ray pre-irradiation without further additives.

Hydrogen bonding effects on the conformational changes of polyglutamates containing long flexible side chains

Abstract The FT-IR spectra for three polyglutamates containing different side chains, poly(γ-methyl α, l -glutamate) (PMLG), poly(γ-hexyl α, l -glutamate) (PHLG), and poly(γ-stearyl α, l -glutamate) (PSLG), were measured and analyzed. Experimental data show that longer side chains induce weaker hydrogen bonds between the carbonyl groups and the amide linkages of the α-helical backbone. Simulated infrared spectra strongly support the infrared spectra with remarkable accuracy. Variable temperature FT-IR measurements on PHLG and PSLG were also performed to examine the effect of temperature on the conformational behavior of the side chains. In the case of PHLG, no perceptible conformational change has been found with increasing temperature. On the other hand, the changes of the characteristic vibrational bands have been found for the infrared spectra of PSLG after the temperature of phase transition. The relative broadness of several bands over 60°C suggests that the increased mobility of the long side chains affects the conformation of the α-helical backbone.

Preparation of an imogolite/poly(acrylic acid) hybrid gel

Many efforts in the field of hydrogels have been focused toward increasing the mechanical strength of the gel using inorganic materials. In this study, we synthesized a hydrogel that has excellent mechanical properties using surface-modified inorganic nanofibers composed of imogolite (Al2SiO3(OH)4), which is a hydrated aluminum silicate that has a hollow tube structure. Gamma ray radiation generates peroxide radicals on the nanofibers (imogolite), resulting in an additive free hybrid hydrogel. Structural optimization was carried out by changing the composition of imogolite and poly(acrylic acid). Chemical bonding between the nanofiber and the polymer was simulated by a cluster model and characterized by wide area Raman spectroscopy. The results indicate that imogolite embedded in a polymer matrix can align along the direction of an elongational force, as confirmed by small angle X-ray scattering (SAXS).

Electrospun tungsten trioxide nanofibers decorated with palladium oxide nanoparticles exhibiting enhanced photocatalytic activity

Tungsten trioxide (WO3) based nanofibers have many advantages as photocatalysts due to its band gap which fits with readily accessible light sources. We successfully fabricated novel palladium oxide (PdO) particles decorated WO3 nanofibers by electrospinning combined with chemical deposition processes, leading to improved photocatalytic efficiency for organic dye degradation up to 86.4%. Morphologies, elemental compositions and structural analyses confirmed the successful uniform decoration of PdO particles along WO3 nanofibers. Photodegradation of methylene blue as a model pollutant in water media was performed under UV and visible light in the presence of fabricated nanofibers as a photocatalyst. As a result, improved photocatalytic activity by PdO decoration was observed compared to commercially available WO3 NFs without PdO, attributed to its ability to hold excited electrons and increase surface area of NFs. This fibrous hybrid catalytic materials platform will open up a new and practical route and stimulate further research to improve photocatalytic performance.

Hollow hyaluronic acid particles by competition between adhesive and cohesive properties of catechol for anticancer drug carrier

The marine mussel-inspired properties of catechol, adhesiveness and cohesiveness, have been applied with pH control to fabricate hollow particles using a silica core and catechol-modified hyaluronic acid (HA-CA) shell for an anticancer drug carrier. The competition between adhesive and cohesive properties of catechol with different pH values leads to various structures, a rough catechol modified HA (HA-CA) shell at pH 5.5, monodisperse spherical silica@HA-CA particles at pH 7.4, and an amorphous HA-CA layer at pH 8.5. The redox transition of catechol with pH is a key factor modulating the behavior of the HA-CA shell on the silica core, which induces strong adhesion of HA-CA to silica at pH 5.5 and structural hardness with cohesive coupling at pH 7.4. In addition, after core removal, the hollow HA-CA particles are followed by loading of anticancer drug, doxorubicin (DOX). DOX loaded HA-CA particles show pH-triggered release behavior and dramatic cytotoxic effect indicating that they are a promising novel anticancer drug carrier.

Urea formaldehyde (UF) microcapsules loaded with corrosion inhibitor for enhancing the anti-corrosive properties of acrylic-based multi-functional PU coatings

The present work focuses on enhancing the anti-corrosive performance of multi-functional polyurethane coatings by encapsulation of the commercially available inhibitors 2-mercaptobenzimidazole and 2-mercapatobenzothiozole, despite their reaction with diisocyanate. Initially, inhibitors were encapsulated by in situ polymerisation of urea and formaldehyde. Formation of microcapsules was confirmed by optical microscopy and FE-SEM. Thermal stability and particle size of microcapsules embedded with inhibitors were estimated by TGA and a particle size analyzer, respectively. Release rates of inhibitors were investigated by UV spectrophotometry. Anti-corrosive coatings were designed by dispersing encapsulated inhibitors in a multi-functional acrylic-based PU coating. The anti-corrosive study of coatings was investigated by the Tafel plot method, weight loss study, immersion study, and FE-SEM of corrosive panels. The impact of microcapsule concentration on the anticorrosive nature of coatings was also evaluated. Our study showed an increase in corrosion inhibition efficiency of PU coatings after incorporation of encapsulated corrosion inhibitors. Comparison of anti-corrosive performance of encapsulated inhibitors demonstrated that 2-MBT is superior to 2-MBI.