Re‐Engineering Poly(Acrylic Acid) Binder toward Optimized Electrochemical Performance for Silicon Lithium‐Ion Batteries: Branching Architecture Leads to Balanced Properties of Polymeric Binders

Silicon is a promising anode material for lithium‐ion batteries with its superior capacity. However, the drastic volume changes during lithiation/delithiation cycles hinder the cycling performance, resulting in particle pulverization, conductivity loss, and an unstable electrode–electrolyte interface. Herein, a series of synthetic polymeric binders, poly(acrylic acid‐co‐tetra(ethylene glycol) diacrylate)—featuring a poly(acrylic acid) (PAA) backbone branched via tetra(ethylene glycol) diacrylate (TEGDA)—are developed that edge toward evidencing well‐balanced properties to confront capacity fading in Si‐based electrodes. The incorporation of ether chain not only leads to the branching architecture of the PAA backbone, thus affecting its mechanical properties, but also promotes the conductivity of Li ions. As a result, a synergistic performance improvement is observed in both half and full cells. The best‐performing cell using a branched PAA binder (bPAA) with a feeding molar ratio ([TEGDA]:[acrylic acid(AA)]) of 0.2 results in a 10% increase in initial capacity and a 31% increase in capacity retention over 100 cycles compared to the linear PAA cell. The cross‐sectional microscopic images of the cycled electrodes reveal that bPAA binders can drastically reduce the electrode expansion. This improvement results from the well‐balanced properties of the polymer design, which could guide further development for more advanced binder materials.     

Fatigue Crack Growth in Epoxy/Aluminum and Epoxy/Steel Joints

The fatigue crack growth rate within epoxy/aluminum and epoxy/steel joints was evaluated as a function of a) type of surface pretreatment, b) water soak, c) fatigue cycle rate (Hz), d) adhesive thickness and e) type of epoxy adhesive.

For both adherends, aluminum and steel, a significant improvement in the fatigue behavior was obtained by use of a mercaptoester coupling agent. After an 8-day, 57°C water soak, the metal surfaces which were pretreated with coupling agent (CA) or by phosphoric acid anodization (PAA) still resulted in cohesive failure, while the controls had higher crack growth rate and showed greater scatter. The room-temperature cure matrix with CA-treated aluminum showed a less dramatic improvement, probably because of a known difference in the application procedure. For the steel joints and room-temperature adhesive the improvement in the fatigue behavior of CA-treated samples was maintained after the 8-day hot water soak. No significant change was found in the fatigue crack growth rate over a frequency range of 1 to 5 Hz, but a significant change was found as a function of the bondline thickness. The room temperature curing adhesive evaluated herein exhibited a much lower fatigue resistance than a heat-cured commercial structural adhesive FM-73.     

Synthesis and characterization of nanostructured PZT encapsulated PVA–PAA hydrogel

Hydrogel/PZT composite was prepared by encapsulating, Pb(Zr_0.52Ti_0.48)O₃ (PZT) nanoparticles in an electroactive (PVA–PAA) hydrogel. The XRD studies confirmed the presence of pure tetragonal phase in PZT with crystallite size of 13 nm in the composite matrix. PZT nanoparticles were found to be embedded in the micro pores of PVA–PAA hydrogel as indicated by the SEM images. The composite shows three step degradation process in the TG/DTA measurements. Dielectric properties were studied from room temperature to 120 °C within wide frequency range of 100 Hz–600 kHz. At room temperature and intermediate frequency range, the composite shows a high dielectric constant of ~225 to 600 and low dielectric loss of 0.08.     

Characterization of the anomalous luminescence properties from self-ordered porous anodic alumina with oxalic acid electrolytes

The pore height and diameter of the nanoscale structure of porous anodic alumina (PAA) film produced by the anodization technique are controllable. The structures can be applied for the fabrication of visible spectral range optical devices. In this study we characterized the luminescence properties of self-ordered PAA films evaporated onto silicon substrates. Anomalous luminescence properties produced by carrier confinement were observed in PAA films fabricated with the introduction of oxalic acid electrolytes during the anodization process. The recombination mechanisms were characterized by measuring the temperature-dependent photoluminescence (PL) spectra. The PL spectra of PAA films show an asymmetrical luminescence profile in the blue emission region. The Gaussian function divides these into two subbands. The subbands originate from two different kinds of oxygen-deficient defect centers, namely, F⁺ (oxygen vacancy with only one electron) and F (oxygen vacancy with two electrons) centers. The F centers are densest at the surface but show a gradual decrease with an increase in the pore wall depth and electrolyte concentration. However, the reverse trend is observed for the F⁺ centers. In strong contrast to the commonly expected trend of a uniform reduction in non-radiative recombination with decreasing lattice temperature, we observed an anomalous low-temperature PL growth and decline between the F and F⁺ centers. Theoretical models corroborate the anomalous temperature behavior. All the calculations are in agreement with the experimental observations.     

Electrochemical behaviour of polyacrylic acid coated gold electrodes: An application to remove heavy metal ions from wastewater

An efficient and low cost preparation method (Diazonium-Induced Anchoring Process) to graft polyacrylic acid (PAA) on the gold substrate has been reported. IR, XPS and AFM techniques were used to characterize the obtained polymer film. The interfacial electrochemistry of the PAA coated gold electrodes was studied by means of impedance spectroscopy and cyclic voltammetry transition techniques. The ability of PAA-grafted onto a gold electrode to reversibly bind or release metal ions was confirmed. As a broad-range chelating material, PAA is able to capture several heavy metal ions at low concentration. The release of those metal ions from the grafted PAA film was obtained under electro-induced-acidification by applying an anodic potential at the electrode to promote a localized water electrolysis. Application of electrochemical-pH-switchable PAA films can be considered within the field of heavy metal waste treatments.     

高聚物絮凝剂在水质处理中应用的现况

论述了高聚物絮凝剂的研究开发与应用的现况,分别对聚丙烯酰胺、淀粉衍生物及甲壳素、壳聚糖类絮凝剂的制备及应用进行分析探讨.     

pH响应性PAA/毒死蜱/氨基化介孔硅缓释体系的制备与性能

以共缩聚法合成氨基化介孔硅,采用浸渍法制备毒死蜱/氨基化介孔硅,并以带负电荷的聚丙烯酸（PAA）为功能分子,通过静电吸附作用制备了具有pH响应的PAA/毒死蜱/氨基化介孔硅缓释体系。利用XRD、N₂吸附-脱附、TEM、SEM、TG、Zeta电位和FTIR对PAA/毒死蜱/氨基化介孔硅的结构进行了表征,并探究了其在不同pH和温度下的释药行为。结果表明,PAA通过静电作用包覆于毒死蜱/氨基化介孔硅的表面。缓释体系的药物释放主要受到PAA的阻碍作用,PAA修饰载药氨基化介孔硅显示出明显的pH响应性,当pH≤7时,其药物释放速率随pH减小而增大,而在偏碱性条件下的释药速率稍大于中性环境。同时,载药体系的释药速率还受到温度的影响。其释药行为可用Korsmeryer-Pappas动力学模型来描述。     

聚丙烯酸法合成锂离子电池正极材料LixMn2O4

以聚丙烯酸为载体通过溶胶凝胶法合成纳米级尖晶石结构的锂离子电池正极材料LixMn2O4(1＜x＜1.12).讨论锂锰摩尔比、烧结温度对产物结构的影响.此外,改进了传统烧结方法,对烧结产物进行回火处理.实验结果表明,烧结温度为550℃时晶化完全,结构完整;当锂锰比为1.082时性能较佳,初始容量为125mAh/g;回火可改善LixMn2O4材料的性能.     

Mass transfer of carbon dioxide in aqueous polyacrylamide solution with methyldiethanolamine

Carbon dioxide was absorbed into aqueous polyacrylamide (PAA) solution containing methyl-diethanolamine (MDEA) in a flat-stirred vessel to investigate the effect of non-Newtonian rheological behavior of PAA on the rate of chemical absorption of CO₂, where the reaction between CO₂ and MDEA was assumed to be a first-order reaction with respect to the molar concentration of CO₂ and MDEA, respectively. The liquid-side mass transfer coefficient (k_L), which was obtained from the dimensionless empirical equation containing the viscoelasticity properties of a non-Newtonian liquid, was used to estimate the enhancement factor due to chemical reaction. PAA with elastic property of non-Newtonian liquid made the rate of chemical absorption of CO₂ accelerate compared with a Newtonian liquid