Designing Semipermeable Hydrogel Shells with Controlled Thickness through Internal Osmosis in Triple-Emulsion Droplets

Hydrogel shells that compartmentalize the water core from the aqueous surrounding provide molecular selectivity on size and charge in transmembrane transport. It is highly demanding to produce thin hydrogel shells to minimize diffusion length and maximize core volume. Here, internal osmosis in water-in-oil-in-water-in-oil (W/O/W/O) triple-emulsion droplets is used to produce thin hydrogel shells enclosing a large water core. The triple-emulsion droplets are prepared to have an ultrathin middle oil layer using a capillary microfluidic device. The innermost water droplet has a higher osmolarity than the outer water layer containing photopolymerizable hydrogel precursors, which pumps water from the outer layer to the core through the ultrathin oil layer by the osmosis. Therefore, the outer layer gets thinner and hydrogel precursors are enriched while the size of the triple-emulsion droplets remains unchanged. Through photopolymerization of precursors and phase transfer from oil to water, hydrogel shells enclosing water core are produced in the water environment; the oil layer is ruptured for molecular exchange through the shells. The thickness and composition of the hydrogel shells are precisely controllable by the osmotic conditions. The shells show a high permeation rate due to the thinness as well as controlled cut-off threshold of permeation for neutral and charged molecules.     

Influence of mixing cycle on the degree of mixing of calcite‐filled polyethylene upon stretching

The mixing cycle‐dependent degree of dispersion and degree of mixing of a calcite (calcium carbonate) agglomerate in high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), and linear low‐density polyethylene (LLDPE) matrices upon stretching was investigated using three different techniques: mechanical property, morphological behavior, and image analyzer analyses. The mechanical properties analyzed in terms of the tensile strength and maximum elongation resulted in that the second mixing was the best for giving a better property for all systems except the LDPE system, which exhibited no significant difference between the second and third mixings. The morphological behavior of the three compounds were different, but no distinctive difference was observed to differentiate the degree of mixing from system to system. The number‐, weight‐, and z + 1‐average diameters of the air hole and the aspect ratio upon the stretching and mixing cycle were calculated to analyze the degree of mixing of the calcite‐filled composites. As a consequence, no difference in the average diameter of the air hole was obtained among the three systems, but the aspect ratios of the air hole varied significantly. Thus, the degree of dispersion and the degree of mixing may be influenced by the average calcite agglomerate size, the average diameter of the air hole, and the aspect ratio upon stretching and mixing cycles. Those factors would be formed by the difference in chemical characteristics upon various microstructures of polyethylene and its molecular weight and molecular weight distribution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 311–321, 2003     

Hydrodynamic trap-and-release of single particles using dual-function elastomeric valves: design, fabrication, and characterization

This paper introduces a simple method for trapping and releasing single particles, such as microbeads and living cells, using dual-function elastomeric valves. Our key technique is the utilization of the elastomeric valve as a dual-function removable trap instead of a fixed trap and a separate component for releasing trapped particles, thereby enabling a simple yet effective trap-and-release of particles. We designed, fabricated, and characterized a microfluidic-based device for trapping and releasing single beads by controlling elastomeric valves driven by pneumatic pressure and a fluid flow action. The fluid flow is controlled to ensure that beads flowing in a main stream enter into a branch channel. A bead is trapped by deflected elastomeric valves positioned at the entrance of a branch channel. The trapped bead is easily released by removing the applied pressure. The trapping and releasing of single beads of 21?μm in diameter were successfully performed under an optimized pressure and flow rate ratio. Moreover, we confirmed that continuous trapping and releasing of single beads by repeatedly switching elastomeric valves enables the collection of a controllable number of beads. Our simple method can be integrated into microfluidic systems that require single or multiple particle arrays for quantitative and high-throughput assays in applications within the fields of biology and chemistry.     

Development of a catalytic combustor for a stationary fuel cell power generation system

The anode off-gas of high temperature stationary fuel cell stacks still includes fuel components such as hydrogen, carbon monoxide, and hydrocarbon due to the innate characteristics of the fuel cell operation. Even though the anode off-gas has fuel contents, the flammability is very limited due to the vapor concentration of the anode off-gas. A catalytic combustor is applied as an off-gas combustor so as to utilize the waste energy of anode off-gas by stimulating a chemical reaction over selected operating conditions. Temperature and flow uniformity in the radial direction are very significant factors of the durability, because the catalytic combustion is carried out on the surface of the catalyst site. On the other hand, the catalyst selection is also very important due to the composition of the anode off-gas. In this study, the flow uniformity is presented prior to a catalyst screening test. From the results of the screening test, where three commercially available catalysts are tested, KIMM-I and KIMM-II are selected as candidates for a catalytic combustor of anode off-gas.     

Enhanced Crystallinity,Dielectric, and Energy Harvesting Performances of Surface‐Treated Barium Titanate Hollow Nanospheres/PVDF Nanocomposites

Enhancement of the energy harvesting performance and dielectric constants of poly(vinylidene fluoride) (PVDF)‐based capacitors is realized by incorporating 16 wt% of surface‐treated BaTiO₃ hollow nanospheres (HNSs) in comparison with the pristine PVDF. The fabricated BaTiO₃ HNSs with particle sizes of ≈20 nm and BET surface area of 297 m² g⁻¹ are treated by three different surface modifiers. The changes in crystallinity of the PVDF containing the surface‐treated BaTiO₃ HNSs are induced by both enlarged surface areas and increased surface functionality of the HNSs. Effects of such surface functionalities on the crystalline, dielectric, and energy harvesting performances of the nanocomposites are systematically investigated to identify the optimal surface modifier to enhance the energy density of the nanocomposites. Consequently, these changes in crystallinity lead to higher dielectric constants (ε′ ≈ 109.6) and energy density (U_e ≈ 21.7 J cm⁻³) with highly retained breakdown strength (E = 3.81 × 10³ kV cm⁻¹) compared to pristine PVDF (ε′ ≈ 11.6 and U_e ≈ 2.16 J cm⁻³ at 3.98 × 10³ kV cm⁻¹), indicating their potential as high energy density capacitors.     

Gravimetric analysis of CO2 adsorption on activated carbon at various pressures and temperatures using piezoelectric microcantilevers

We investigated the adsorption and desorption of CO(2) on activated carbon using piezoelectric microcantilevers. After coating the free end of a cantilever with activated carbon, variations in the resonance frequency of the cantilever were measured as a function of CO(2) pressure, which is related to mass changes due to the adsorption or desorption of CO(2). The pressure-dependent viscous damping effects were compensated in the calculation of the CO(2) adsorption capacity of the activated carbon by comparing the frequency differences between the coated and uncoated cantilevers. The mass sensitivity of the piezoelectric cantilever was found to be better than 1 pg. The fractional coverage of CO(2) agreed with a Langmuir adsorption isotherm, indicating that a submonolayer of adsorbed CO(2) occurred on the surface of the activated carbon under the experimental conditions. The heat of adsorption was determined using the Clausius-Clapeyron relation and the fractional coverage of CO(2) at various temperatures and pressures.     

Performance Optimization of Vertical Nanowire‐based Piezoelectric Nanogenerators

The integrated nanogenerator (NG) based on vertical nanowire (NW) arrays is one of the dominant designs developed to harvest mechanical energy using piezoelectric nanostructures. Finite element method (FEM) simulations of such a NG are developed using ZnO NWs in compression mode to evaluate its performances in term of piezoelectric potential generated, capacitance, induced mechanical energy, output electrical energy, and efficiency. This evaluation is essential to correctly understand NG operation. Three main issues are highlighted. The mechanical and electrical structures of the NG as an integrated system are optimized, and strategies for concentrating the mechanical strain field in the NWs and increasing the force sensitivity are developed. In addition, the influence of NWs length and diameter on NG performances is investigated. The optimization results in a piezoelectric nano composite material where global performances are improved by mean of long and thin NWs.     

Triboelectric Nanogenerator as an Active UV Photodetector

Self‐powered nanosensors and nanosystems have attracted significant attention in the past decades and have gradually become the most desirable and promising prototype for environmental protection/detection because no battery is needed to power the device. Therefore, in this paper a design is proposed for a self‐powered photodetector based on triboelectric nanogenerator (TENG) configuration. 3D dendritic TiO₂ nanostructures are synthesized as the built‐in UV photodetector as well as the contact material of the TENG. The cost‐effective, robust, and easily fabricated TENG‐based photodetector presents superior photoresponse characteristics, which include an excellent responsivity over 280 A W^?1, rapid rise time (18 ms) and decay time (31 ms), and a wide detection range of light intensity from 20 μW cm^?2 to 7 mW cm^?2. In the last part of the paper, a stand‐alone and self‐powered environmental sensing device is developed by applying poly(methyl methacrylate) (PMMA) substrates and springs to assemble the TENG‐based photodetector. These results indicate that the new prototype sensing device based on the TENG configuration shows great potential as a self‐powered photodetector.