Effects of defect dipoles on tunable dielectric response in relaxor ferroelectric ceramics

Tunable dielectric materials have drawn much attention due to their wide applications including capacitors and microwave tunable devices. Ferroelectrics materials have special spontaneous polarization which can be reversibly switched by an external electric field. Therefore, tunable dielectric constant can be easily achieved in ferroelectrics. However, the study of nonlinear dielectric response induced by defect dipoles is rarely concerned. Here, we report the effects of defect dipoles on tunable dielectric response under alternative current (AC) and direct current (DC) electric field in defect dipoles introduced Pb(Lu_1/2Nb_1/2)O₃–PbTiO₃ ceramics. A modified Rayleigh model is proposed to successfully characterize dielectric nonlinearity and reveals the interaction between domain walls and defect dipoles. The defect dipoles had more sensitive effect on dielectric response under AC field than that of defect dipoles-free samples. The drop of intrinsic dielectric contribution under AC field results from the detriment effect of defect dipoles. The irreversible contribution is altered by the movements of defect dipoles under AC field, subsequently inducing the nonlinearity of dielectric response. Samples with defect dipoles have larger tunable scope of dielectric properties than that of defect dipoles-free samples. The present work discovers the potential of application of defect dipoles-tuned dielectric response ferroelectrics in devices which requires both high AC and DC biases, and help to better understand the complex dielectric response of ferroelectrics.     

Polyurethane foaming with CO2 adducts from C8 alkyl grafted polyethyleneimines: Optimization of the grafting rate and application of the blowing agents

We previously explored a series of CO₂ adducts from alkylated polyethylenimines with C₄ to C₁₆ alkyl side chains, serving as climate-friendly blowing agents for polyurethanes (PUs). Among them, the polyethylenimine with C₈ alkyl (2-ethylhexyl) side chains demonstrated the highest foaming efficiency. In this study, we further changed the grafting rate of the C₈ alkyl, from 7 to 16%, and investigated the effects of the resulting blowing agents on the foaming process. For both foaming systems containing a castor oil-derived polyol (Polycin T-400) or a poly(propylene glycol) polyol (Polyether 4110), the CO₂ adducts with a grafting rate of 13% displayed the best foaming performance in terms of high dispersibility in the foaming systems, homogenous cellular morphology, and good mechanical properties. Moreover, the 13%-C₈-alkylated blowing agent demonstrated high suitability for the foaming systems from biomass-sourced polyols (like Polycin T-400). Therefore, the optimized CO₂-adduct blowing agent could replace the currently used climate-changing hydrochlorofluorocarbons and hydrofluorocarbons, as well as might contribute to the development of future renewable PU foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48752.     

Polytetrafluoroethylene-intercalated MXene membranes with good photothermal performance for enhanced laser ignition

Photothermal effect has been widely used in many areas such as cancer therapy, photothermal energy harvesting, and laser ignition. However, exploring reliable and efficient free-standing energy converter for enhancing the photothermal performance is still a challenge. Herein, free-standing membrane based on two-dimensional MXene (Ti₃C₂) nanosheets and polytetrafluoroethylene (PTFE) was fabricated and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, which demonstrated a drastic temperature rise by laser irradiation and was further used as energy converter for enhancing the photothermal performance of laser ignition. Furthermore, the initiating power of the laser initiator can be largely reduced by adding a thin layer of MXene/PTFE membrane above the B/KNO₃ cylinder. This work can give great promise for MXene-based membranes as the laser energy converter for reducing the initiating energy and promote the development of laser initiators with low initiating energy.     

Synthesis of 3,13-diglycidyloxypropyloctaphenyl double-decker polyhedral oligomeric silsesquioxane and the thermal reaction properties with thermosetting phenol-formaldehyde resin

3,13-Diglycidyloxypropyloctaphenyl double-decker silsesquioxane (EP-DDSQ) was synthesized by process of alkaline hydrolysis condensation of phenyltrimethoxysilane and corner capping reaction of methyldichlorosilane, followed by hydrosilylation with allyl glycidyl ether, and the resultant structure was confirmed by fourier transform infrared spectrometer (FTIR) and nuclear magnetic resonance (NMR), respectively. The thermosetting phenol-formaldehyde (PF) resin was then modified by EP-DDSQ, and the reactivity of PF resin with EP-DDSQ and thermal pyrolysis of modified cured resin were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The surface morphologies of modified resins at high temperature were characterized with field emission scanning electron microscope (FESEM), and chemical structure of modified resins was analyzed through X-ray photoelectron spectrometer (XPS). The results showed that the appropriate addition of EP-DDSQ did not affect the curing temperature of the PF resin itself, but could improve the heat resistance of the system. When the amount of EP-DDSQ added was 10%, the initial degradation temperature of PF resin was increased by 49.31°C, and when the amount of EP-DDSQ added was 16%, the char yield of which was reached up to 61.39%, compared with that of pure PF resin (TGA_1,000°C of 57.62%) at Ar atmosphere. More importantly, the modified resin formed a regular and dense layer of SiC and SiO_x ceramic on the surface after ablation in the muffle furnace at 800°C air atmosphere, which is very important for ablative resistant materials.     

Synthesis of pH-responsive isolated soy protein/carboxymethyl chitosan microspheres for sustained pesticide release

In order to improve the utilization rate of avermectin (AVM), a complex was prepared by electrostatic self-assembly using isolated soy protein (ISP) and carboxymethyl chitosan (CMCS) for loading AVM to obtain ISP/CMCS@AVM microspheres. The encapsulation efficiency (EE), sustained release property, ultraviolet (UV) protective ability, and toxicity of the microspheres were evaluated, and the release kinetics of AVM from the microsphere at different pHs were investigated. The results demonstrated that the average particle size of ISP/CMCS@AVM was 283.95 nm, and the EE reached 88.42% for AVM after denaturation. After 70 h of exposure to UV light, the residual rate of AVM in ISP/CMCS@AVM was 78.12%, which was significantly higher than 35.18% in the AVM emulsion. Moreover, the formulation imparted pH sensitivity and sustained-release property to AVM and was consistent with the Korsmeyer–Peppas model, controlled by Fick diffusion. Finally, the insecticidal toxicity of ISP/CMCS@AVM did not differ significantly from that of unmodified AVM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48358.     

Innovene工艺聚丙烯装置反应器结块原因分析与控制

对Innovene聚丙烯工艺进行分析,探讨了导致粉料结块的原因,并分别从催化剂类型、反应控制、催化剂分散性、催化剂喷嘴问题、共聚牌号生产和牌号切换等进行了分析,列举了各种原因导致的结块。从生产实际出发,针对性地采取措施,对工艺控制、设备设施、生产操作和检修维护等进行优化,减少或者消除反应器结块现象,保障Innovene工艺聚丙烯装置生产的顺利进行。     

Fabrication of novel silicon carbide-based nanomaterials with unique hydrophobicity and microwave absorption property

Novel SiC-based nanomaterials, namely the nitrogen and aluminum co-doped SiC@SiO₂ core-shell nanowires and nitrogen-doped SiO₂/Al₂O₃ nanoparticles, have been fabricated through a facile thermal treatment process based on the chemical vapor deposition and vapor-liquid reaction. These nanomaterials show remarkable hydrophobicity with a water contact angle (CA) over 140°, which are aroused by the surface zigzag morphology of the nanostructures and the hydrocarbyl groups generated during the preparation process. Moreover the nanocomposites also exhibit relatively prominent microwave absorption (MA) properties in the frequency range of 2.0-18.0 GHz. The minimum reflection loss (RL) value as low as −23.68 dB can be observed at 14.16 GHz when the absorber thickness is 2.6 mm with a loading rate of 16.7 wt%. And the nanocomposites-based absorbent can achieve an effective absorption bandwidth (RL < −10 dB) of 4.48 GHz with the absorbent thickness of 2.5 mm. This enhanced microwave attenuation performance can be attributed to multiple polarizations and perfect impedance matching conditions, as well as multiple internal reflections. These marvelous properties make these N and Al co-doped SiC@SiO₂ core-shell nanowires and N-doped SiO₂/Al₂O₃ nanoparticles display extensive application potential as MA materials in harsh environment.     

MES表面活性剂的工业化精制工艺

将α-磺基脂肪酸甲酯钠盐（MES）产品（含活性物质70%）在加热熔融的状态下滴加到50~55℃低沸点水溶性有机溶剂中,经冷却、结晶、过滤和干燥,得到高纯MES粉剂产品。考察了低沸点水溶性有机溶剂种类、原料与溶剂的投料质量比、冷却温度和结晶时间等工艺条件对产品回收率、活性物质量分数和过筛率的影响,得到了最佳纯化精制工艺：以甲醇为溶剂,5 kg MES,MES与溶剂的投料质量比为1：3,冷却温度为5℃,结晶时间为120 min,干燥时间60 min,干燥温度45℃,溶剂使用3次。本工艺条件下,所制得MES粉剂产品回收率大于98%,含活性物质量分数大于93.0%,产品在40℃密封保存12 h后,过0.850 mm筛孔的筛,过筛率达100%。     

子午线轮胎硫化时间的仿真优化

通过建立模具、轮胎和硫化胶囊仿真模型,对比轮胎关键部位硫化过程中实际测温与仿真的温度-时间曲线,对仿真结果进行验证。结果表明,对轮胎温度场的模拟仿真分析能比较准确地预测轮胎硫化过程不同位置点温度变化的趋势,可以作为优化轮胎硫化工艺的一种手段。     

获各琦铜矿利用采空区及废旧巷道预热冬季入风流的研究

获各琦铜矿利用地温预热的原理,设计了冬季井筒防冻通风系统。该预热系统经过一年多的运行,采空区及废旧巷道可使约63m^3/s的冷空气由-26℃预热到+2℃以上,有效地降低了冬季期间进风井的预热压力及预热成本,节省了大量能源消耗。在实践上证明了利用采空区及废旧巷道预热冬季入风流在技术上的有效性、经济上的合理性和安全上的可靠性。