Hongsik Byun

Swelling Behavior and Drug Release of Poly(vinyl alcohol) Hydrogel Cross-Linked with Poly(acrylic acid)

Thermal cross-linking method of poly(vinyl alcohol) (PVA) using poly(acrylic acid) (PAA) was carried out on PVA/PAA hydrogels. The level of gelation was measured in the PVA/ PAA hydrogels with various PAA contents. The swelling behavior at various pHs showed that the swelling kinetics and water contents of the PVA/ PAA hydrogels reached equilibrium after 30 h, and the time to reach the equilibrium state decreased with increasing PAA content in the hydrogel. The water content increased with increasing pH of the buffer solution. The permeation and release of the drug were tested using indomethacin as a model drug. The permeated and released amounts of the drug increased with decreasing the PAA content because of the low free volume in the hydrogel due to the higher cross-linking density. The kinetic profile of drug release at various pHs showed that all samples reached the equilibrium state within the 5 h.

PVdF/graphene oxide hybrid membranes via electrospinning for water treatment applications

Membrane materials based on poly (vinylidene fluoride) (PVdF) have received great attention recently due to their outstanding mechanical property and chemical resistance. However, this material can easily cause a membrane fouling problem due to its hydrophobic nature. This paper describes how to overcome this problematic issue by incorporating hydrophilic graphene oxide (GO) into PVdF-based membranes. Herein, PVdF nanofiber membranes loaded with GO were prepared via an electrospinning method and the hybrid membranes were characterized for water treatment applications. Graphene oxide sheets were initially prepared by the Hummers method. The pore property of the PVdF/GO hybrid nanofiber membrane for microfiltration (MF) applications was controlled by systematically increasing the number of nanofiber layers and thermal treatment. These resulting materials were characterized by SEM, FT-IR, UV-Vis, Raman spectroscopy, and tensometer. The overall results showed the reliable formation of the hybrid membranes which possessed controlled pore-diameters (∼0.2 micron) and narrow distribution. Based on contact angle tests, these PVdF/GO nanofiber hybrid membranes exhibited very hydrophilic characteristics. In addition, the hybrid membrane showed high pure water flux results up to 3 times and outstanding flux decline with 0.1 g L−1 Kaolin solutions compared to a neat PVdF nanofiber membrane. Based on all these results, it can be speculated that the incorporation of GO into PVdF could also improve the antifouling ability of the membrane system and will allow for their use as a water-treatment membrane.

Thermally tunable catalytic and optical properties of gold-hydrogel nanocomposites.

We have developed a very simple approach for preparing physically embedded gold cores in a temperature-responsive hydrogel polymer nanoparticle under fluorescent light irradiation. The complete encapsulation of the multiple gold core nanoparticles is confirmed by the catalytic reduction of 4-nitrophenol, whose reactivity is significantly retarded above the lower critical solution temperature (LSCT) due to the deswelled polymer structure; its increased hydrophobicity slows the access of hydrophilic reactants to the cores. Since these gold cores are physically embedded in the polymer nanoparticles, further growth of the cores is reliably achieved in situ under light irradiation. Interestingly, the resulting composite nanoparticles exhibit reversible solution color changes as well as absorption bands from the visible to near-IR regions below and above the LSCT.

Sunlight-Induced Synthesis of Various Gold Nanoparticles and Their Heterogeneous Catalytic Properties on a Paper-Based Substrate

This work describes the light-induced preparation of various gold nanoparticles and demonstrates their possible use as efficient photothermal heating materials and practical heterogeneous catalysts under the irradiation of a solar-based light after being loaded onto a paper-based substrate. The synthesis of gold nanoparticles was accomplished under the irradiation of daily sunlight and a solar-simulated light with an intensity that was closely adjusted to the one-sun condition. Tunable sizes of gold nanoparticles were systematically controlled by the ratio of trisodium citrate and gold chloride ions, particularly with the solar-simulated light source. The size distribution and absorption properties of the resulting nanoparticles were thoroughly characterized by scanning electron microscope, dynamic light scattering, and UV-visible spectroscopy. The broad-band solar-based light sources were found to be efficient external stimuli to induce/enhance the formation of various gold nanoparticles at room temperature. As gold nanoparticles typically exhibit efficient light-induced heating properties due to their strong absorption bands, these nanoparticles were physically embedded on a filter paper to examine their photothermal heating properties and heterogeneous catalytic activity in the reduction of 4-nitrophenol under the irradiation of the solar-simulated light. As expected, the gold-loaded filter papers exhibited a systematic increase of temperature as a function of the gold nanoparticle concentration and enhanced catalytic property under the irradiation of the light, presumably caused by the photothermally induced heating property of the loaded gold nanoparticles. Overall, solar-based light sources can offer dual functions for the synthesis and application of metal nanoparticles possessing strong absorption bands.

One-pot synthesis of various Ag–Au bimetallic nanoparticles with tunable absorption properties at room temperature

This report describes the formation of gold-coated silver bimetallic nanoparticles prepared by the one-pot synthetic approach which involves the subsequent reduction of silver and gold ions at ambient conditions. The reduction of silver ions by excess L-ascorbic acid initially led to the formation of silver cores. This step was followed by the addition of gold ions into the preformed cores, resulting in the formation of silver-core gold-shell type bimetallic nanoparticles at room temperature. This process systematically allowed for the formation of various bimetallic nanoparticles which exhibited tunable absorption properties corresponding to the visible and near-IR regions. The thickness of the gold shells and the diameter of the silver-core nanoparticles were readily controlled; the morphological and structural properties of the resulting bimetallic nanoparticles were thoroughly analyzed by SEM/TEM, DLS, and UV–Vis spectrophotometry. The overall results demonstrated not only that these gold-coated silver nanoparticles were reliably prepared by our one-pot synthetic approach, but also that their optical properties were tunable in the visible and near-IR areas as a function of the core size and shell thickness.

Hydrogenation of cyclohexene with perfluorinated cation- and anion-exchange membranes supported platinum☆

Abstract A perfluorinated cation-exchange membrane (Nafion) and an anion-exchange membrane (Tosflex) supported platinum (Pt) were prepared by ion-exchanging with Pt(NH 3 ) 2 2+ or K 2 PtCl 4 , respectively. They were then reduced either with a large excess of NaBH 4 or under hydrogen in a glass-lined stainless-steel bomb at 80°C and 20.6 MPa for 3 h. UV visible spectra indicated that 70–80% of ion exchange was completed. The rate of hydrogenation of cyclo(c-)hexene in methanol with both platinised membranes showed similar trends, increasing with an increase in the Pt loading on the membrane. However, catalytic activity expressed as turnover frequency (TOF) reached a maximum(0.23 s −1 ) at about a 0.5% Pt loading. When the Tosflex-Pt was reduced by H 2 , partial Pt reduction was obtained, resulting in a low TOF. The rate of hydrogenation of c-hexene over a range of pressures indicated that the system was not diffusion limiting after 1.1 MPa.

A strategy to design biocompatible polymer particles possessing increased loading efficiency and controlled-release properties

Temperature-responsive poly(N-isopropylacrylamide), or poly(NIPAM), layers were reliably prepared around guest molecule (i.e., rhodamine B)-loaded mesoporous silica (SiO2) particles via thermally- and light-induced radical polymerizations. Subsequent removal of the sacrificial SiO2 particles with dilute hydrofluoric acid led to the formation of biocompatible polymer particles possessing a high dose of rhodamine B. The use of SiO2 core templates not only led to the formation of a uniform coating of the poly(NIPAM) layers, but also increased the stability of the guest molecule, rhodamine B, throughout polymerization. Interestingly, the light-induced radical polymerization method resulted in much less inevitable leaching and decomposition of azo-based guest molecules. The structural information and overall dye-loading efficiency of the mesoporous particles and the final polymer particles were then thoroughly examined by electron microscopes, dynamic light scattering, and fluorescence spectroscopy. As poly(NIPAM)-based particles exhibited significant swelling and deswelling properties above and below the lower critical solution temperature, the controlled-release properties of the poly(NIPAM) particles prepared by both methods were also evaluated. Generally, the dye-loaded poly(NIPAM) particles prepared by the light-induced approach resulted in a thinner coating of the polymer layers and exhibited much higher loading and tunable release profiles of the loaded guest molecules than those prepared by the thermally-induced polymerization. Given these features, the generalization of our strategy to design chemotherapeutically interesting drug-loaded polymer particles that are biocompatible and sensitive to external stimuli will allow for the further development of novel biomedical delivery and treatment systems.

Synthesis and Evaluation of PVA-CN Additive for High Thermal Stability of Lithium Secondary Battery Electrolyte

Currently liquid electrolyte having good ion-conductivity and high electrochemical stability has been used for the lithium secondary battery. But it has been reported there was a serious problem in the high temperature stability. In this study, the development of PVA-CN cyanoethyl polyvinyl alcohol additive which is used in lithium secondary battery electrolyte was carried out with two steps; the first step was the dissolution of PVA raw materials, and the second step was the synthesis of PVA-CN. The thermal property of the prepared PVA-CN was quantitatively analyzed using TGA. The significantly improved thermal stability of the electrolytes containing PVA-CN additives was also confirmed by monitoring swelling behavior of the membranes at high temperature, i.e. 29% less swelling effect, although they exhibited slightly lower ion conductivity, about 6% lower than commercially available electrolytes. This finding clearly suggests the possibility of preventing the swelling issue at high temperature which is the main cause of dangerous accidents from secondary battery systems.

In Situ Formation of Gold Nanoparticles within a Polymer Particle and Their Catalytic Activities in Various Chemical Reactions

Composite materials consisting of nanoscale gold particles and protective polymer shells were designed and tested as catalysts in various chemical reactions. Initially, the systematic incorporation of multiple gold nanoparticles into a poly(N-isopropylacrylamide) particle was achieved by an in situ method under light irradiation. The degree of gold nanoparticle loading, along with the structural and morphological properties, was examined as a function of the amount of initial gold ions and reducing agent. As these gold nanoparticles were physically-embedded within the polymer particle in the absence of strong interfacial interactions between the gold nanoparticles and polymer matrix, the readily-accessible surface of the gold nanoparticles with a highly increased stability allowed for their use as recyclable catalysts in oxidation, reduction, and coupling reactions. Overall, the ability to integrate catalytically-active metal nanoparticles within polymer particles in situ allows for designing novel composite materials for multi-purpose catalytic systems.

Polymer particles filled with multiple colloidal silica via in situ sol-gel process and their thermal property

The in situ formation of dielectric silica (SiO2) particles was carried out in the presence of temperature-responsive poly(N-isopropylacrylamide) particles. Unlike the typical sol-gel method used to prepare various SiO2 particles, the highly uniform growth of SiO2 particles was achieved within the cross-linked polymer particles (i.e., the polymer particles were filled with the SiO2 particles) simply by utilizing interfacial interactions, including the van der Waals attractive force and hydrogen bonding in nanoscale environments. The structural and morphological features as well as the thermal behaviors of these composites were thoroughly examined by electron microscopes, dynamic light scattering, and thermal analyzers. In particular, the thermal properties of these composites were completely different from the bare polymer, SiO2 particles, and their mixtures, which clearly suggested the successful incorporation of multiple SiO2 particles within the cross-linked polymer particles. Similarly, titanium oxide (TiO2) particles were easily embedded within the polymer particle template which exhibited improved overall properties. As a whole, understanding in situ formation of nanoscale inorganic particles within polymer particle templates can allow for designing novel composite materials possessing enhanced chemical and physical properties.