Jun Seo Park

A polyoxometalate coupled graphene oxide–Nafion composite membrane for fuel cells operating at low relative humidity

Polymer electrolyte fuel cells operating at elevated temperature and low relative humidity (RH) have been investigated by utilizing a polyoxometalate coupled graphene oxide–Nafion membrane. A phosphotungstic acid (PW) coupled graphene oxide–Nafion (Nafion/PW-mGO) membrane showed enhanced proton conductivity compared with pristine and recast Nafion membranes. The Nafion/PW-mGO hybrid membrane exhibited a maximum power density of 841 mW cm−2, whereas the pristine Nafion membrane showed a power density of 210 mW cm−2 operated at 80 °C under 20% RH. In comparison, our hybrid membrane showed a 4-fold higher maximum fuel cell power density when operated at 80 °C under 20% RH, than that of a state-of-the-art pristine membrane (Nafion-212). The remarkably enhanced performance of the Nafion/PW-mGO composite membrane was mainly attributed to the reduction of ohmic resistance by the hygroscopic solid acids, which can retain water in their framework through hydrogen bonding with protons at elevated temperatures and facilitates proton transport through the membrane.

Fabrication and characterization of electrospun curcumin-loaded polycaprolactone-polyethylene glycol nanofibers for enhanced wound healing

This study focused on the development of biomedicated electrospun nanofiber mats for preventing wound infections and accelerating wound healing. Polycaprolactone (PCL) nanofibers-loaded curcumin (Cur) and polyethylene glycol (PEG) were generated by an electrospinning technique. The change in surface morphology of the electrospun nanofibers to porous surface after immersion was obtained by field emission scanning electron microscopy (FE-SEM). The biological characteristics of the Cur-loaded PCL-PEG nanofiber mats such as cell viability, cell attachment, anti-inflammatory and antibacterial properties, and in vivo wound healing capability were examined. The blending of PEG with PCL resulted in the formation of pores on the nanofibers after immersion, which supports cell viability and proliferation. The mouse myoblast cell line C2C12 showed about 80% viability on the Cur-loaded PCL-PEG nanofiber mat. SEM images showed that the cells could extremely attach and spread out over the surface of the Cur-loaded PCL-PEG nanofiber mat. The inclusion of 0.5 wt% Cur (with respect to PCL) in both the PCL and PCL-PEG blended nanofiber mats inhibited excessive production of nitric oxide (NO) in RAW264.7 mouse macrophages and exhibited good antibacterial activity against Staphylococcus aureus (S. aureus). In vivo wound healing showed that the treatment using Cur-loaded PCL-PEG nanofiber mat significantly increased the rate of wound closure (99%) on day 10 as compared that using PCL nanofiber mat (59%). These results suggest that the PCL nanofiber matrix containing Cur and PEG can facilitate wound healing with cell proliferation and anti-inflammatory properties.

Fabrication of form-stable poly(ethylene glycol)-loaded poly(vinylidene fluoride) nanofibers via single and coaxial electrospinning

Two types of form-stable phase change material based on poly(ethylene glycol)-loaded poly(vinylidene fluoride) (PVDF) nanofibers were fabricated via single and coaxial electrospinning. Blends of two different kinds of poly(ethylene glycol) (PEG600 and PEG1000) were used as the phase change material (PCM) and PVDF was used as supporting polymers in the PCM-loaded electrospun PVDF nanofibers. By single electrospinning, SiO2 was added into the PEGs-loaded PVDF to prevent PEGs leakage and to maintain the shape of the nanofibers during the melting and solidifying processes. The addition of SiO2 also increased the mechanical strength of the nanofibers. By coaxial electrospinning, the core/shell structured nanofibers, in which the PEGs and PVDF were the active core and protective shell layers, respectively, were fabricated. The microstructure of the e-spun nanofibers was investigated by FE-SEM. TEM images show that PEGs were encapsulated by PVDF shell. The ATR-FTIR analysis and water contact angle measurements confirm that good core/shell-structured nanofibers were obtained when the core feed rate was lower than 4.0 µL/min. During the water immersion test, the PEGs on the surface of the PVDF/SiO2 composite nanofibers were dissolved, while no leakage of PEGs from the core/shell-structured nanofibers was observed. A hot oven and a DSC cycling tests were conducted to evaluate the thermal stability. These results show that the PEGs-loaded core/shell nanofibers had better thermal stability than the PEGs-loaded PVDF/SiO2 composite nanofibers. Therefore, the non-woven mats of the core/shell-structured nanofibers could have extensive applications in thermal energy storage and fabrication of smart textile.