Water-repellent coating: formation of polymeric self-assembled monolayers on nanostructured surfaces

In this paper, we suggest a facile and effective method for water-repellent coating of oxide surfaces. As a coating material, we synthesized a new random copolymer, referred to as poly(TMSMA-r-fluoroMA), by the radical polymerization of 3-(trimethoxysilyl)propyl methacrylate (TMSMA) and a fluoromonomer(?) bearing methacrylate moiety (fluoroMA). The random copolymer was designed to consist of a 'surface-reactive part' (trimethoxysilyl group) for anchoring onto oxide-based surfaces and a 'functional part' (perfluoro group) for water repellency. The polymeric self-assembled monolayers (pSAMs) of poly(TMSMA-r-fluoroMA) were constructed on three different aluminum oxide substrates, such as flat, concave-textured, and nanoporous plates, and the static water contact angle of each surface before and after the formation of pSAMs was measured. The formation of pSAMs resulted in significantly enhanced hydrophobicity compared with the corresponding bare surfaces. In particular, among three poly(TMSMA-r-fluoroMA)-coated surfaces, the nanoporous plate showed the highest water-repellent property, with a static contact angle of ～163°, which is indicative of superhydrophobic surfaces.     

In-situ growth of copper sulfide nanocrystals on multiwalled carbon nanotubes and their application as novel solar cell and amperometric glucose sensor materials

Single-crystalline copper sulfide (beta-Cu2S) nanocrystals (NCs) were grown in situ on multiwalled carbon nanotubes (MWCNTs) by the solvothermal method. The morphology of the Cu2S NCs was varied from spherical particles (av size=4 nm) to triangular plates (av size=12 nm) by increasing the concentration of the precursors. The lattice matching between Cu2S and the MWCNTs would be an important factor in the growth of Cu2S NCs on the MWCNTs. The solar cells and the amperometric glucose sensors fabricated using these Cu2S-MWCNT hybrid nanostructures respond more sensitively than those using the Cu2S NCs (or MWCNTs) alone. The utilization of the active Cu2S NCs through direct binding with the conductive MWCNTs would lead to excellent performance of these nanodevices.     

Photocurrent imaging of p-n junctions in ambipolar carbon nanotube transistors

We use scanning photocurrent microscopy (SPCM) to investigate the properties of internal p-n junctions in ambipolar carbon nanotube (CNT) transistors. Our SPCM images show strong signals near metal contacts whose polarity and positions change depending on the gate bias. SPCM images analyzed in conjunction with the overall conductance also indicate the existence and gate-dependent evolution of internal p-n junctions near contacts in the n-type operation regime. To determine the p-n junction position and the depletion width with a nanometer scale resolution, a Gaussian fit was used. We also measure the electric potential profile of partially suspended CNT devices at different gate biases, which shows that induced local fields can be imaged using the SPCM technique. Our experiment clearly demonstrates that SPCM is a valuable tool for imaging and optimizing electrical and optoelectronic properties of CNT based devices.     

Nanocrystalline particle coatings on alpha-alumina powders by a carbonate precipitation and thermal-assisted combustion route

We have suggested ultrafine particle coating processes for preparing nanocrystalline particle coated alpha-alumina powders by a carbonate precipitation and thermal-assisted combustion route, which is environmentally friendly. The nanometric ammonium aluminum carbonate hydroxide (AACH) as a precursor for coating of alumina was produced from precipitation reaction of ammonium aluminum sulfate and ammonium hydrogen carbonate. The synthetic crystalline size and morphology were greatly dependent on pH and temperature. By adding ammonium aluminum sulfate solution dispersed the alpha-alumina core particle in the ammonium hydrogen carbonate aqueous solution, nanometric AACH with a size of 5 nm was tightly bonded and uniformly coated on the core powder due to formation of surface complexes by the adsorption of carbonates, hydroxyl and ammonia groups on the surface of aluminum oxide. The synthetic precursor rapidly converted to amorphous- and y-alumina phase without significant change in the morphological features through decomposition of surface complexes and thermal-assisted phase transformation. As a result, the nanocrystalline polymorphic particle coated alpha-alumina core powders with highly uniform distribution were prepared from the route of carbonate precipitation and thermal-assisted combustion.     

Soft-chemical synthesis and electrochemical characterization of multicomponent Mn(1-x-y)Co(x)Ni(y)O2 nanostructures

Nanostructured Mn(1-x-y)Co(x)Ni(y)O2 metal oxides are synthesized by one-pot hydrothermal reaction at low temperature. From powder X-ray diffraction and field emission-scanning electron microscopic analyses, it is found that the crystal structure and crystal morphology of the present materials are tunable by the control of the composition of precursor. 1D nanowires with alpha-MnO2-type structure are prepared with low substitution rate of Co and Ni, while the increase of substituent contents leads to the formation of delta-MnO2-structured 3D nanospheres consisting of 2D nanoplates. According to X-ray absorption near edge spectroscopy and chemical analyses, mixed valent Co(III)/Co(IV) and divalent Ni(II) ions are stabilized in the octahedral Mn sites of alpha-MnO2- and delta-MnO2-structures. The electrochemical measurements clearly demonstrate that the present nanostructured materials show promising electrode performances for lithium secondary batteries.     

Properties and interaction of cement with polymer in the hardened cement pastes added absorbent polymer

Ordinary Portland cement mixed with various amounts of absorbent polymer in the form of sodium acrylate ((–CH–)_nCOONa) have been studied. As the content of absorbent polymer increased, heat evolution of samples decreased up to 1.15 wt % of absorbent polymer addition and conversely increased over 1.75 wt %. Flexural strength of cement paste with absorbent polymer was improved more than 20%. As the content of absorbent polymer increased, the porosity values decreased and mean pore diameter shifted to small pore diameter region. Flexural strength of ordinary Portland cement paste had a linear correlation with non-evaporable water content but, that of cement paste with absorbent polymer deviated from a linear correlation with non-evaporable water content. The chemical difference between cement pastes with and without absorbent polymer was found by the inductively coupled plasma-atomic emission spectroscopy and the infrared spectroscopy. For the infrared spectra of absorbent polymer, bands at 1416 and 1560 cm^{– 1} were assigned to C–O single bond and C=O double bond respectively, namely, unidentate complex. As the curing time increased, the absorption bands near 1416 cm^{– 1} shifted to longer wave number and the absorption bands near 1560 cm^{– 1} to shorter wave number and finally bidentate complex was formed. Absorbent polymer released sodium ions to pore solution under the basic condition of pH 12.5–13.5 and became polyacrylic acid. Then some of these polyacrylic acid were crosslinked with others by calcium ions leached from cement grains. Calcium ion was regarded as a central charge connecting the negative parts in carbon-oxygen polarization of absorbent polymer' functional groups.     

Computational investigation on the flow characteristics in beam dyeing process

Abstract

Ensuring uniform addition of coloring material to the fabric is an essential requirement in the textile dyeing process. Beam dyeing machine consists of a special beam, the barrel of which is evenly perforated with holes. The dye liquor is forced into the fabric material through this beam. For uniform fabric coloring, an equal distribution of the dye liquor through the porous beam has to be ensured. The present methodology employs theoretical and computational fluid dynamics aspects of beam dyeing process to obtain better performance. The analysis of a beam with a single row of branches shows that nonuniformity increases with an increase in inlet mass flow. Further beam flow distribution with and without fabric are studied for different parameters, such as branch diameter, inlet mass flow rate, operating conditions, and flow reversal. The present results provide guidelines to improve the levelness of the dye distribution in the fabric material.     

Ultra-Fine Control of Silica Shell Thickness on Silver Nanoparticle-Assembled Structures

To study the distance-dependent electromagnetic field effects related to the enhancement and quenching mechanism of surface-enhanced Raman scattering (SERS) or fluorescence, it is essential to precisely control the distance from the surface of the metal nanoparticle (NP) to the target molecule by using a dielectric layer (e.g., SiO₂, TiO₂, and Al₂O₃). However, precisely controlling the thickness of this dielectric layer is challenging. Herein, we present a facile approach to control the thickness of the silica shell on silver nanoparticle-assembled silica nanocomposites, SiO₂@Ag NPs, by controlling the number of reacting SiO₂@Ag NPs and the silica precursor. Uniform silica shells with thicknesses in the range 5–40 nm were successfully fabricated. The proposed method for creating a homogeneous, precise, and fine silica coating on nanocomposites can potentially contribute to a comprehensive understanding of the distance-dependent electromagnetic field effects and optical properties of metal NPs.     

Prevalence and Characteristics of Phenicol-Oxazolidinone Resistance Genes in Enterococcus Faecalis and Enterococcus Faecium Isolated from Food-Producing Animals and Meat in Korea

The use of phenicol antibiotics in animals has increased. In recent years, it has been reported that the transferable gene mediates phenicol-oxazolidinone resistance. This study analyzed the prevalence and characteristics of phenicol-oxazolidinone resistance genes in Enterococcus faecalis and Enterococcus faecium isolated from food-producing animals and meat in Korea in 2018. Furthermore, for the first time, we reported the genome sequence of E. faecalis strain, which possesses the phenicol-oxazolidinone resistance gene on both the chromosome and plasmid. Among the 327 isolates, optrA, poxtA, and fexA genes were found in 15 (4.6%), 8 (2.5%), and 17 isolates (5.2%), respectively. Twenty E. faecalis strains carrying resistance genes belonged to eight sequence types (STs), and transferability was found in 17 isolates. The genome sequences revealed that resistant genes were present in the chromosome or plasmid, or both. In strains EFS17 and EFS108, optrA was located downstream of the ermA and ant(9)-1 genes. The strains EFS36 and EFS108 harboring poxtA-encoding plasmid cocarried fexA and cfr(D). These islands also contained IS1216E or the transposon Tn554, enabling the horizontal transfer of the phenicol-oxazolidinone resistance with other antimicrobial-resistant genes. Our results suggest that it is necessary to promote the prudent use of antibiotics through continuous monitoring and reevaluation.