Kyoung-Hee Shin

Photocatalytic activity of TiO2 film containing Fe2O3 via plasma electrolytic oxidation

This study investigated the photocatalytic activity of an Fe containing TiO2 film produced in the FePO4 electrolyte via the plasma electrolytic oxidation (PEO) method. For this purpose, the PEO process was carried out on titanium substrate under ac condition in two different alkaline electrolytes containing K3PO4 and FePO4 respectively. The structure, chemical composition and constituent phases of the PEO treated samples were analysed via SEM, X-ray photoelectron spectroscopy and X-ray diffraction. The optical properties of the samples were also examined by an ultraviolet–visible spectrophotometer. In terms of the photocatalytic activity judging from the decomposition of methylene blue under visible light illumination, the sample formed in the FePO4 electrolyte was better than that in the K3PO4 electrolyte due to the incorporation of an Fe compound that has a narrow band gap.

Pore size effect on cell response via plasma electrolytic oxidation

Using a plasma electrolytic oxidation (PEO) process, this study investigated how the pore size of the coating surface influences the growth of osteoblast cells and their morphology in pure titanium. With this aim, PEO coatings were applied using four different electric and electrolyte conditions to vary the mean pore sizes of the coatings from ∼2 to ∼5 μm. In vitro examinations showed that the osteoblast cells on the surface of the coating with ∼2 μm pores had grown healthily with good attachment by multiple pseudopodia connections; cells were highly proliferated, compared to those of other samples. In addition, the coating with ∼2 μm pores showed the highest cell viability among the samples.

Structurally Stable Attractive Nanoscale Emulsions with Dipole-Dipole Interaction-Driven Interdrop Percolation

This study introduces an extremely stable attractive nanoscale emulsion fluid, in which the amphiphilic block copolymer, poly(ethylene oxide)-block-poly(ϵ-caprolactone) (PEO-b-PCL), is tightly packed with lecithin, thereby forming a mechanically robust thin-film at the oil-water interface. The molecular association of PEO-b-PCL with lecithin is critical for formation of a tighter and denser molecular assembly at the interface, which is systematically confirmed by T2 relaxation and DSC analyses. Moreover, suspension rheology studies also reflect the interdroplet attractions over a wide volume fraction range of the dispersed oil phase; this results in a percolated network of stable drops that exhibit no signs of coalescence or phase separation. This unique rheological behavior is attributed to the dipolar interaction between the phosphorylcholine groups of lecithin and the methoxy end groups of PEO-b-PCL. Finally, the nanoemulsion system significantly enhances transdermal delivery efficiency due to its favorable attraction to the skin, as well as high diffusivity of the nanoscale emulsion drops.

Fabrication and stabilization of nanoscale emulsions by formation of a thin polymer membrane at the oil–water interface

This study introduces a robust approach for the fabrication of extremely stable oil-in-water nanoemulsions in which the interface is stabilized by assembly of amphiphilic poly(ethylene oxide)-block-poly(e-caprolactone) (PEO-b-PCL) copolymers. Phase inversion emulsification, induced by variation of the water volume fraction, facilitated effective assembly of the block copolymers at the oil–water interface. Subsequent application of simple probe-type sonication reduced the droplet size of the precursor emulsions to approximately 200 nm. The prepared nanoemulsions were surprisingly stable against drop coalescence and aggregation, as confirmed by analysis of changes in the droplet size after repeated freeze–thaw cycling and by monitoring the creaming kinetics under conditions of high ionic strength and density mismatch. The results highlight that good structural assembly of the PEO-b-PCL block copolymers at the oil–water interface generated a mechanically flexible but tough polymer film, thereby remarkably improving the emulsion stability.