Thermoreversible hydrogels. VIII. Effect of a zwitterionic monomer on swelling behaviors of thermosensitive hydrogels copolymerized by N‐isopropylacrylamide with N,N′‐dimethyl (acrylamidopropyl) ammonium propane sulfonate

A series of thermosensitive hydrogels were prepared from the various molar ratios of N‐isopropylacrylamide, zwitterionic monomer, N,N′‐dimethyl (acrylamidopropyl) ammonium propane sulfonate (DMAAPS), and N,N′‐methylene‐bis‐acrylamide. The influence of the amount of DMAAPS in the copolymeric gels on the swelling behaviors in water, various saline solutions, and various temperatures was investigated. Results indicated that the higher the DMAAPS content in the hydrogel system, the higher the swelling ratio and the gel transition temperature. In the saline solution results showed that, when the salt concentration was greater than the minimum salt concentration (MSC) of poly(DMAAPS), the deswelling behavior of the N‐isopropylacrylamide gel was suppressed more effectively when more DMAAPS was added into the copolymeric gels; but the swelling ratios of the present copolymeric gels did not significantly change while the salt concentration was lower than the MSC of poly(DMAAPS). In addition, only the sample containing 12 mol % DMAAPS (D4) exhibited an antipolyelectrolyte's swelling behavior when the salt concentration was greater than the MSC of poly(DMAAPS). In other words, only when the amount of DMAAPS added into the gel is over some proportion, can the hydrogel show an antipolyelectrolyte's swelling behavior in concentrated salt solution. In saline solutions, the anion effects were greater than the cation effects in the presence of common anion (Cl⁻) with different cations and common cation (K⁺) with different cations for these gels. Finally, the more DMAAPS content in the hydrogel, the higher the diffusion coefficient in dynamic swelling. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2170–2180, 1999     

Micro-Cup Architecture for Printing and Coating Asymmetric 2d-Material-Based Solid-State Supercapacitors

High energy density micro-supercapacitors (MSCs) are in high demand for miniaturized electronics and microsystems. Research efforts today focus on materials development, applied in the planar interdigitated, symmetric electrode architecture. A novel “cup & core” device architecture that allows for printing of asymmetric devices without the need of accurately positioning the second finger electrode here have been introduced. The bottom electrode is either produced by laser ablation of a blade-coated graphene layer or directly screen-printed with graphene inks to create grids with high aspect ratio walls forming an array of “micro-cups”. A quasi-solid-state ionic liquid electrolyte is spray-deposited on the walls; the top electrode material -MXene inks- is then spray-coated to fill the cup structure. The architecture combines the advantages of interdigitated electrodes for facilitated ion-diffusion, which is critical for 2D-material-based energy storage systems by providing vertical interfaces with the layer-by-layer processing of the sandwich geometry. Compared to flat reference devices, volumetric capacitance of printed “micro-cups” MSC increased considerably, while the time constant decreased (by 58%). Importantly, the high energy density (3.99 µWh cm⁻²) of the “micro-cups” MSC is also superior to other reported MXene and graphene-based MSCs.     

Modeling of the impact of cycling operating conditions on durability of polymer electrolyte fuel cells and its sensitivity analysis

In the paper, the impact on durability of polymer electrolyte membrane fuel cells is investigated when varying operating conditions applied in accelerated stress tests. By this, the electric potential cycling protocol in given by a non-symmetric square profile. The electrochemical degradation of a catalyst layer is caused by platinum ion dissolution and oxide coverage. These mechanisms are described by the one-dimensional Holby–Morgan model with a modified Butler–Volmer equation for the reaction rates. For efficient numerical solution of the underlying nonlinear reaction-diffusion system, a variable time-step implicit-explicit method is suggested. Computer simulations predict durability for the catalyst by using a linear extrapolation up to the full platinum surface blockage. A parameter sensitivity analysis is presented on different time scales and measures how the platinum mass loss is impacted by the variation of specific parameters.     

基于FEA的蜂窝铝芯平压分析

利用非线性有限元分析软件MSC.Marc对蜂窝铝芯平压过程进行了模拟计算,得到了应力分布图和应力沿路径分布曲线,结合图形和曲线分析了蜂窝铝芯的应力分布规律和变形特点。结果表明,平压过程中应力集中出现在交棱处,在外力作用下这些位置最容易发生失稳,而面板中间的应力值始终相对交棱处应力值较小;由于交棱和壁板中部受到的约束不同,最大应力分布区域与变形最大区域不一致。