Eun-Ho Sohn

Silver-perfluorodecanethiolate complexes having superhydrophobic, antifouling, antibacterial properties

Silver-perfluorodecanethiolate complexes having superhydrophobic, antifouling, antibacterial properties were prepared by a reaction of silver nitrate with perfluorodecanethiol. When the silver nitrate to perfluorodecanethiol molar ratio was 1/2, silver-perfluorodecanethiolate complexes having hierarchical micro-/nano-sized wire shapes were obtained, and they showed superhydrophobic and antifouling properties. After UV irradiation, silver nanoparticles were generated on the wires and exhibited antibacterial properties.

Inhibition of bacterial adhesion on well ordered comb-like polymer surfaces

The surfaces of comb-like poly(oxyethylene) derivatives with n-alkylsulfonyl side groups were more effective at reducing Pseudomonas aeruginosa adhesion than the surfaces of common materials such as polystyrene, poly(methyl methacrylate), poly(dimethylsiloxane), fluorinated polyacrylate, and glass. When the comb-like poly(oxyethylene) was mixed with polystyrene and poly(methyl methacrylate), the topology and roughness of the surfaces varied according to the mixture compositions. However the surface energies of the mixtures were close to that of the comb-like poly(oxyethylene) in the range of 21-23 mN/m and bacterial adhesion resistances of the mixture surfaces were also comparable to that of the pure comb-like poly(oxyethylene) surface.

Effect of n-alkyl and sulfonyl groups on the wetting properties of comblike poly(oxyethylene)s and stick-slip behavior.

The influence of side chain length and sulfonyl moiety on the molecular structures and wettability behavior of poly(oxyethylene)s with alkyl sulfonyl side chains (CH(3)-nSE, n = 1, 2, 3, 4, 5, 6, 8, 10), where n is the number of the carbon atom in the n-alkyl side group, was investigated. CH(3)-nSEs having shorter side chains (n < 5) do not have ordered structures, and their surfaces were found to be more polar than those of CH(3)-nSEs having longer side chains (n ≥ 5). The CH(3)-nSEs having longer side chains show double-layered lamellar structures (n ≥ 5) with well-aligned side chains and low surface energies in the range 21.2-25.8 mN/m. Interestingly, stick-slip behavior was observed only on the surfaces of CH(3)-3SE and CH(3)-4SE when water was used as the test liquid. The surface deformation at the three-phase line was generated from interactions between water and sulfonyl groups, and the optimum side chain lengths were believed to cause the stick-slip behavior.

Comb-like polymer blends of poly(oxyethylene)s with CH3-terminated and CF3-terminated alkylsulfonylmethyl side chains: Effect of terminal CF3 moiety on the surface properties of the blends

The surface properties of comb-like polymer blends of poly(oxyethylene)s having CH(3)-terminated and CF(3)-terminated alkylsulfonylmethyl side chains were studied. These side chains were found to be well oriented on the surface of the blends, while being phase separated, forming various surface morphologies composed of holes, islands, or connected islands, because of their immiscibility resulting from their different polarities. The domain size of each polymer on the blend surface was found to be almost linearly proportional to the bulk compositions of the mixture, and the CF(3)-terminated alkylsulfonylmethyl side chain domains were found to be located in the lower region of the surface. The polar CF(3)-terminal groups in the lower regions were deemed to control the surface properties, because the contact angles and stick-slip behaviors of the blends containing more than 40 mol% of poly(oxyethylene) with CF(3)-terminated side chains were almost identical.

Liquid crystal alignment properties of n-alkylsulphonylmethyl-substituted polyoxyethylenes

The liquid crystal (LC) alignment properties of LC cells fabricated with films of n-alkylsulphonylmethyl-substituted polyoxyethylenes (#S-PEO, # = 4, 6, 7, 8 and 10), where # is the number of carbon atoms in the n-alkyl side groups having different n-alkyl chain length, were investigated as a function of the rubbing density. The LC cells made from unrubbed #S-PEO (# ≥8) films having more than eight carbon atoms in the n-alkyl side groups showed homeotropic LC alignment. The homeotropic LC alignment behaviour correlated well with the surface energy values of the unrubbed #S-PEO films; homeotropic LC alignment was observed when the surface energy values of the unrubbed #S-PEO films were smaller than about 21.62 mJ m−2. The LC cells made from rubbed #S-PEO (# ≥7) films having more than seven carbon atoms with a rubbing density of 150 showed homeotropic LC alignment. It was also found that the tilt angle of the LCs on the rubbed #S-PEO films was affected not only by the n-alkyl chain length of the polymers, but also by the rubbing density, regardless of the surface energy value of the #S-PEO film.

Wettability of the morphologically and compositionally varied surfaces prepared from blends of well ordered comb-like polymer and polystyrene

Phase-separated surfaces of blends of polystyrene (PS) and well ordered comb-like polymer, poly[(oxy(decylsulfonylmethyl)ethylene)] (CH(3)-10SE), were prepared by spin casting polymer mixtures. Various surface morphologies, such as holes, islands, connected islands and pillars, were prepared by changing the blend compositions. Due to the influence of the CH(3)-10SE domain with a well ordered molecular conformation, a very low energy surface (≈22mN/m) was created, which is close to the value of the pure polymer (≈20mN/m), even when the blends contained only 20wt.% of the pure polymer. Furthermore, by selective etching the PS domain in the blend surfaces, the advancing contact angles of water and n-hexadecane were highly increased from 113.5° and 43.2° for the pure CH(3)-10SE surface to 133.3° and 67.2° for the CH(3)-10SE structural surfaces with holes prepared using the solvent etching method, respectively. The result of the water advancing contact angles measured on the samples immersed in water over 20days showed that the film stability of CH(3)-10SE could be improved considerably by even adding small amounts of PS.

Biocompatible Ag nanoparticle-embedded poly(2-hydroxyethyl methacrylate) derivative films with bacterial adhesion-resistant and antibacterial properties

Polymeric nanocomposite films of poly(2-hydroxyethyl methacrylate) (PHEMA) derivative, with ester side groups containing well-dispersed Ag nanoparticles, were prepared, using a very simple coating and reduction process. The nanocomposite films were stable in water because the matrix polymer, PHEMA derivative with ester side groups is relatively hydrophobic, while Ag nanoparticles are well dispersed in the polymer matrix, due to the oxygen-rich ester side groups of the polymer. By integrating the antibacterial effect of Ag nanoparticles onto the bacterial adhesion-resistant and biocompatible characters of the PHEMA derivative, polymer-Ag nanocomposite films having biocompatible, bacterial adhesion-resistant, and antibacterial properties could be produced. Moreover, a very small amount of Ag nanoparticles was found to greatly increase the stability of the polymer film in water, a leading to extending the applicable window in biological fields.

Ultra-hydrophobic sticky polymer surfaces formed by water-induced surface deformation

Surface properties of poly(oxyethylene)s with alkyl thioether side chains (CH3-nTE; n=carbon atoms in the side chain) were investigated. CH3-nTEs having shorter side chains (n=6, 8, 10) did not have ordered structures, while those with longer chains (n=12, 14) showed well-ordered, lamellar structures with side chain crystalline domains. Accordingly, CH3-12TE and CH3-14TE film surfaces were much more enriched with hydrophobic alkyl side chains than CH3-8TE and CH3-10TE surfaces. However, CH3-12TE and CH3-14TE films had smaller water contact angles (≈114°) than CH3-8TE and CH3-10TE films (>130°). This unexpected behavior is ascribed to the formation of very rough CH3-8TE and CH3-10TE film surfaces (Rrms>100nm) on contact with water. The CH3-10TE/poly(methyl methacrylate) (PMMA) surfaces also showed high water contact angles (>125°), even with low CH3-10TE content (30wt%), because the CH3-10TE moiety roughened the surfaces. Furthermore, ultra-hydrophobic sticky behavior was observed for CH3-nTEs (n=8, 10) and CH3-10TE/PMMA surfaces.

Bacterial adhesion-resistant poly(2-hydroxyethyl methacrylate) derivative for mammalian cell cultures.

In an attempting to find new biomaterials for mammalian cell culture, PHEMA derivatives with ester side groups are synthesized by one-step polymer-analogous reaction. These polymers show excellent antifouling properties against S. epidermidis and P. aeruginosa while their cytotoxicity and proliferation activity for HDF cell are on a similar level as commercially available TCPS. The interesting bioadhesion property is systematically correlated with surface properties of the PHEMA derivatives.

Synthesis of pillar and microsphere-like magnesium oxide particles and their fluoride adsorption performance in aqueous solutions

We synthesized pillar and microsphere-like MgO particles and their fluoride removal performance. Samples of MgO were synthesized by calcination of precursors derived from MgCO3·3H2O and characterized using field emission scanning electron microscopy, X-ray diffraction, and N2 adsorption-desorption isotherms. The fluoride removal performance of the MgO samples was investigated in terms of adsorption kinetics and adsorption equilibrium. The effects of pH and the presence of other anions on the fluoride adsorption were also considered. The adsorption capacities of pillar and microsphere-like MgO particles were 151.51 and 166.66 mg/g, respectively. The pH of the aqueous solutions did not significantly affect the fluoride adsorption at pH 9 or lower. Except for phosphate, the effect of co-existing anions on fluoride adsorption was not considerable. Fluoride removal occurred through the substitution of hydroxyl groups on the surface of MgO with fluorides.