Jaewoong Lee

Antibacterial cotton fibers treated with silver nanoparticles and quaternary ammonium salts.

Cotton fibers were treated chemically with glycidyltrimethylammonium chloride (GTAC), a quaternary ammonium salt, and coated with silver nanoparticles/3-mercaptopropyltrimethoxysilane (3-MPTMS) to increase the antibacterial efficacy. The coating process was accomplished by soaking the cotton fibers into a GTAC solution followed by a dry-cure method, and silver colloid/3-MPTMS solution was then applied at 43°C for 90min. The properties of the cotton fibers were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis. SEM showed a rough surface when the cotton fibers were treated with GTAC/3-MPTMS/silver nanoparticles due to the increasing surface attachment. The existence of silver and 3-MPTMS on the cotton fibers was confirmed by XPS. The cotton fibers treated with both GTAC and silver nanoparticles showed synergistic antibacterial properties against P. aeruginosa.

Improved Antimicrobial Efficacy of m-Aramid

Poly(m-phenyleneisophthalamide), m-aramid has no adjacent α-hydrogen of a nitrogen-halogen bond causes dehydrohalogenation. This fact proposes that m-aramid is one of good antimicrobial precursors. To enhance the surface area of m-aramid, electrospinning was employed. Scanning electron microscopy(SEM) was conducted to inspect the morphology change of m-aramid. The surface area of regular and electrospun m-aramid was calculated. Swatch test was applied to measure antimicrobial activity of the samples. The results showed that within 10 min contact time the electrospun m-aramid inactivated Escherichia coli KCTC 1039 (Gram-negative bacteria) with 8 log reductions.

The Deformation of Polydimethylsiloxane (PDMS) Microfluidic Channels Filled with Embedded Circular Obstacles under Certain Circumstances

Experimental investigations were conducted to determine the influence of polydimethylsiloxane (PDMS) microfluidic channels containing aligned circular obstacles (with diameters of 172 µm and 132 µm) on the flow velocity and pressure drop under steady-state flow conditions. A significant PDMS bulging was observed when the fluid flow initially contacted the obstacles, but this phenomenon decreased in the 1 mm length of the microfluidic channels when the flow reached a steady-state. This implies that a microfluidic device operating with steady-state flows does not provide fully reliable information, even though less PDMS bulging is observed compared to quasi steady-state flow. Numerical analysis of PDMS bulging using ANSYS Workbench showed a relatively good agreement with the measured data. To verify the influence of PDMS bulging on the pressure drop and flow velocity, theoretical analyses were performed and the results were compared with the experimental results. The measured flow velocity and pressure drop data relatively matched well with the classical prediction under certain circumstances. However, discrepancies were generated and became worse as the microfluidic devices were operated under the following conditions: (1) restricted geometry of the microfluidic channels (i.e., shallow channel height, large diameter of obstacles and a short microchannel length); (2) operation in quasi-steady state flow; (3) increasing flow rates; and (4) decreasing amount of curing agent in the PDMS mixture. Therefore, in order to obtain reliable data a microfluidic device must be operated under appropriate conditions.

Water disinfection activity of cellulose filters treated with polycarboxylic acid and aromatic amine

A cellulose filter for water disinfection was developed using a polycarboxylic acid and an aromatic amine via a simple process with water as a solvent. 1,2,3,4-Butanetetracarboxylic acid/m-phenylenediamine solution was applied to cellulose filters using a pad–dry–curing process. The surfaces of treated cellulose filters were examined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The liquid permeabilities of treated cellulose filters were determined by capillary flow porometry, and their water disinfection efficacies were measured by non-pressure-driven filtration. Chlorinated cellulose filters disinfected Escherichia coli- and Staphylococcus aureus-containing solutions to a much higher degree than observed for nonchlorinated cellulose filters.

In Vitro Studies on a Microfluidic Sensor with Embedded Obstacles Using New Antibacterial Synthetic Compounds (1-TDPPO) Mixed Prop-2-en-1-one with Difluoro Phenyl

This paper describes the use of an analytical microfluidic sensor for accelerating chemo-repellent response and strong anti-bacterial 1-(Thien-2-yl)-3-(2, 6-difluoro phenyl) prop-2-en-1-one (1-TDPPO). The chemically-synthesized antimicrobial agent, which included prop-2-en-1-one and difluoro phenyl groups, was moving through an optically transparent polydimethylsiloxane (PDMS) microfluidic sensor with circular obstacles arranged evenly. The response, growth and distribution of fluorescent labeling Pseudomonas aeruginosa PAO1 against the antimicrobial agent were monitored by confocal laser scanning microscope (CLSM). The microfluidic sensor along with 1-TDPPOin this study exhibits the following advantages: (i) Real-time chemo-repellent responses of cell dynamics; (ii) Rapid eradication of biofilm by embedded obstacles and powerful antibacterial agents, which significantly reduce the response time compared to classical methods; (iii) Minimal consumption of cells and antimicrobial agents; and (iv) Simplifying the process of the normalization of the fluorescence intensity and monitoring of biofilm by captured images and datasets.

Effective surface attachment of Ag nanoparticles on fibers using glycidyltrimethylammonium chloride and improvement of antimicrobial properties

Functional poly(m-phenylene isophthalamide), m-aramid (known as Nomex®) fibers with antimicrobial properties were prepared by applying quaternary ammonium salts (such as glycidyltrimethylammonium chloride (GTAC)) in combination with silver nanoparticles (AgNPs). The fibers treated by this simple process exhibited enhanced antimicrobial activity. In the coating process, the m-aramid fibers were immersed in a GTAC solution and reacted via the pad-dry-cure process. The GTAC-treated m-aramid fibers were then reacted with an Ag colloid solution at 40 °C for 90 min to prepare GTAC/AgNP-treated m-aramid fibers. Scanning electron microscopy was used to confirm the surface morphology of the m-aramid fibers treated with GTAC and AgNPs. Changes in the chemical composition before and after GTAC and AgNP treatment were analyzed by scanning electron microscopy with energy-dispersive X-ray spectroscopy. The tensile strength of the GTAC/AgNP-treated m-aramid fibers declined by about 3.5% compared to that of untreated m-aramid fibers. Durability of the AgNPs on the m-aramid fibers treated with GTAC/AgNPs was demonstrated through a washing-fastness test, indicating 76% retention after five washing cycles. The antimicrobial activity analysis showed that the synergistic antimicrobial properties of the GTAC/AgNP-treated m-aramid fibers resulted in efficacy against P. aeruginosa.

Physical Properties of PDMS (Polydimethylsiloxane) Microfluidic Devices on Fluid Behaviors: Various Diameters and Shapes of Periodically-Embedded Microstructures

Deformable polydimethylsiloxane (PDMS) microfluidic devices embedded with three differently-shaped obstacles (hexagon, square, and triangle) were used to examine the significant challenge to classical fluid dynamics. The significant factors in determining a quasi-steady state value of flow velocity (v)QS and pressure drop per unit length (∆P/∆x)QS were dependent on the characteristic of embedded microstructures as well as the applied flow rates. The deviation from the theoretical considerations due to PDMS bulging investigated by the friction constant and the normalized friction factor revealed that the largest PDMS bulging observed in hexagonal obstacles had the smallest (∆P/∆x)QS ratios, whereas triangle obstacles exhibited the smallest PDMS bulging, but recorded the largest (∆P/∆x)QS ratios. However, the influence of (v)QS ratio on microstructures was not very significant in this study. The results were close to the predicted values even though some discrepancy may be due to the relatively mean bulging and experimental uncertainty. The influence of deformable PDMS microfluidic channels with various shapes of embedded microstructures was compared with the rigid microchannels. The significant deviation from the classical relation (i.e., f~1/Re) was also observed in hexagonal obstacles and strongly dependent on the channel geometry, the degree of PDMS deformation, and the shapes of the embedded microstructures.

m-Aramid Films in Diverse Coagulants

m-Aramid dissolved in N,N-dimethylacetamide (DMAc), were coagulated in different coagulants such as water, methanol, ethanol, propanol and butanol. Various concentrations and temperatures of the coagulants were also used to evaluate dyeing properties of coagulated m-aramid films. Field emission scanning electron microscopy (FE-SEM) was employed to investigate the surface morphology of m-aramid films. Wide angle X-ray diffraction (WAXD) was conducted in order to measure crystallinity change of m-aramid fibers and films. WAXD patterns showed that crystallinity of m-aramid fibers was reduced after film formation. In addition, color depth (K/S value) was measured and the results revealed that the film coagulated in water possessed fairly enhanced color depth.

Investigation of binary blends of m-aramid and sodium ionomer: Mechanical, thermal, and morphological properties

Novel hybrid blend with the composition of m-aramid and sodium ionomers with different weight ratio percentage were prepared by the solution blending technique. The prepared composite films were characterized by the Fourier-transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The phase structure, compatibility, and morphologies of the composite film were investigated with SEM, DMA, XRD, and transmission electron microscopy (TEM) analysis. The TGA of the composite films shows improvement in the thermal stability. The temperature corresponding to 5% (T 5%) weight losses is in the range of 101–414°C. The storage modulus (in the range of 01.55–3.0 GPa) and glass transition temperature (in the range of 244–276°C) decreased with an increase in the content of sodium ionomers. The tensile strength of the composite films is in the range of 160–185 MPa. This effective approach shows a potential application in the field of m-aramid-based composites.

Orientation measurement of graphically simulated nanoscale electrospun fibrous structures using particle-based modeling and 2-D metaball fitting

Purpose The purpose of this paper is to provide an efficient tool for simulating electrospinning process in virtual 3D space and optimizing experimental parameters. The fiber orientation from virtual or real electrospinning process can be easily measured using the image analysis technique. Using the semi-implicit Euler integration, the time integration can be more fast and stable, which enabled optimization of the electrospinning process. Also boundary conditions can be easily adopted during conjugate gradient matrix solving step. Design/methodology/approach To simulate the electrospinning process, the authors have adopted a particle-based modeling technique using the molecular dynamics theory, which is known to be suitable for modeling materials with nonlinear and nonhomogeneous behavior such as fibers or fabrics. Gravitational, tensional, and electrostatical forces and their Jacobians were carefully defined and chosen to maintain the stability of the governing equation. Preconditioned conjugate gradient method was used to solve the matrix iteratively with boundary conditions. The 2-D metaball fitting technique, which was applied in the previous research (Sul et al., 2009) on experimental nanofiber scanning electron microscopy images, was utilized with virtual nanofiber images. A staircase function and a new shading language were proposed to automatically calculate the orientation and radius distribution of the graphically simulated electrospun fiber structures. The automatic measurement procedure was verified via graphically designed virtual replica images. Also the orientation tendency acquired from the simulation was compared with that of experimental data. Findings Simulation result of fiber orientation showed linear relationship with the collecting drum speed. Use of particle-based method generated a simple system to simulate electrospinning process. Originality/value The semi-implicit Euler integration was applied to the electrospinning process and the final linear system was numerically stable to solve.