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.     

Collective reflection strategy for moderating conformity tendency and promoting reflective judgment performance

Reflective judgement is crucial for medical-related practitioners in dealing with controversial issues. However, the conformity phenomenon is likely to occur and interfere with reflective judgement learning during interactive activities. Effective strategies are required to moderate the conformity behaviour tendency (CBT) and improve reflective judgement performance (RJP). This study demonstrates two significant results: (a) Compared with the guided self-reflection learning strategy, the online collective reflection (OCR) learning strategy effectively weakened the learners' general CBT while dealing with professional controversial issues; and (b) a significantly negative correlation between the RJP achieved and the change of CBT in online environment was detected in the OCR group. The implications and potential applications in higher education were discussed. Further studies are needed to confirm the long-term effects and the extending application to other professional studies.     

Porous Si3N4 ceramics prepared by aqueous gelcasting using low–toxicity DMAA system: Regulatable microstructure and properties by monomer content

In this study, the low–toxicity monomer N, N–dimethylacrylamide (DMAA), serving as both gelling agent and pore–forming agent, was adopted to fabricate porous Si₃N₄ ceramics with a regulatable microstructure and property by aqueous gelcasting. Results indicate that monomer content played an important role in regulating and optimizing the properties of sintered bodies. With increasing monomer content (5.94–30.69?wt%), both slurry viscosity (maximum 0.14?Pa?s at 95.40 s^?1) and green body strength (11.35–49.23?MPa) exhibited monotonic increasing trends, demonstrating superior mechanical properties to those obtained using the neurovirulent acrylamide (AM) gelling system. The increased monomer content not only improved porosity, but also promoted α→β–Si₃N₄ transformation as well as β–Si₃N₄ grain growth through enhancing the connectivity of interlocking pores and accelerating the vapor phase transport during liquid–phase sintering. These variations in phase composition and microstructure derived from the varied monomer content further resulted in monotonic changes in porosity (40.32–51.50%), mean pore size (0.27–0.38?μm), flexural strength (202.77–132.15?MPa), fracture toughness (2.93–2.32?MPa?m^1/2), dielectric constant (3.48–2.78) and loss (3.52–3.09?×?10^?3) at 10?GHz for sintered bodies, displaying an excellent comprehensive properties. This study suggests a promising prospect for DMAA in preparation of high–performance porous Si₃N₄ ceramics by aqueous gelcasting.     

Microstructure and hydrogen absorption/desorption properties of Mg24Y3M (M = Ni,Co, Cu,Al) alloys

Ternary alloys with the nominal composition of Mg₂₄Y₃M (M = Ni, Co, Cu, Al) have been fabricated by using vacuum induction melting method. Their microstructure and phase composition are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The isothermal hydrogen absorption and desorption kinetics are measured by a Sievert's-type apparatus. The dehydrogenation behaviors of the full hydrogenated alloys are also analyzed by differential scanning calorimetry (DSC) method. Results show that each and every alloy has a distinct multiphase structure containing the main phase Mg₂₄Y₅ and some amount of Mg. Intermetallic compounds of YCo₂ and Al₂Y are detected in the M = Co and M = Al alloy, while long-period stacking ordered (LPSO) phase can be also observed in M = Ni and M = Cu alloy. The hydrogen absorption and desorption kinetics shows a decreased trend in the following order: (M = Ni) > (M = Al) > (M = Co) > (M = Cu). The M = Ni alloy has the best hydrogen storage performance among the investigated alloys. The dehydrogenation activation energy (E_a) of the M = Ni alloy decreases to 66 kJ/mol, and its decomposition peak temperature is also reduced to 313 °C. Moreover, the p–c–T (pressure-composition isotherms) curves of the studied alloys are also discussed.     

Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers

Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp² bonding between carbon atoms.     

Evaluation and verification of the virgin–recycled mixing ratio of polypropylene plastic

This study has analyzed the properties of blended polypropylene (PP) specimens and employed statistical analysis to develop a method for determining the virgin–recycled mixing ratio of a specimen. Morphological observations and analyses of thermal and mechanical properties were conducted to examine specimen properties. The results were incorporated into regression analysis to create relationship equations. The results revealed that the melt temperature ranged between 167 and 169 °C, melt index (MI) ranged between 7.59 and 18.36 g/10 min, viscosity decreased when the amount of recycled PP and the rotation speed increased, the maximum decomposition temperature decreased with an increase in recycled PP content and increased with the heating rate, activation energy (E_a) ranged between 39.91 and 12.07 kcal/mol, Young’s modulus ranged between 1121.1 and 1910.2 MPa, and impact strength ranged between 37.94and 49.41 J/m (no significant trends). Scanning electron microscopy showed unbroken fibrils distributed on the fracture surface of Specimens 1–3. Additionally, the tensile strain of these specimens was comparatively high. The fracture surfaces of the specimens showed favorable compatibility after undergoing impact tests. The results of regression analysis indicated that the mixing ratio achieved significant correlations with E_a, MI, and Young’s modulus. Thus, regression and multiple regression analysis were performed to create relationship equations.     

采用酯类捕收剂PZA提高铜、银回收率的选矿试验研究

在某硫化铜矿浮选过程中,进行了酯类捕收剂PZA与丁基黄药、丁基铵黑药、Z200等对比研究,发现PZA对铜、银具有良好的选择性,与丁基黄药组合效果更佳。原矿铜、银品位分别为0.28%和8.50g/t情况下,采用铜硫混合浮选—铜硫分离工艺流程,最终获得了铜精矿Cu品位21.58%、回收率83.94%,Ag品位500.10g/t、回收率62.99%的技术指标,较好的实现了银在铜精矿的定向富集。