改性POSS/苯并环丁烯树脂复合材料的制备与性能

通过分别在2种含有苯并环丁烯单元的基体树脂——4-(1’,1’-二甲基-1’-乙烯基)硅基苯并环丁烯均聚物(P(4-DMVSBCB))及4-(1’,1’-二甲基-1’-乙烯基)硅基苯并环丁烯和苯乙烯共聚物(P(4-DMVSBCB-r-St))中添加苯并环丁烯改性的笼型倍半硅氧烷(BCB-POSS),制备出介电性能优异的BCB树脂/POSS复合材料。通过红外研究了复合材料的固化过程,并通过阻抗分析、热重分析、邵氏硬度研究了不同BCB-POSS含量对复合材料的介电性能、耐热性能及硬度的影响。结果表明,在固化过程中,POSS表面的BCB四元环开环与基体树脂中的BCB四元环发生Diels-Alder反应形成共价键;复合材料的介电常数随着BCB-POSS的添加量增加而降低,当添加量达到40%时,介电常数可降低至2.35;BCB-POSS的添加使材料的耐热性能和硬度都有提高,并随着BCB-POSS的添加量的增加而上升。

Global pattern and change of cropland soil organic carbon during 1901-2010: Roles of climate, atmospheric chemistry, land use and management

Soil organic carbon(SOC)in croplands is a key property of soil quality for ensuring food security and agricultural sustainability,and also plays a central role in the global carbon(C)budget.When managed sustainably,soils may play a critical role in mitigating climate change by sequestering C and decreasing greenhouse gas emissions into the atmosphere.However,the magnitude and spatio-temporal patterns of global cropland SOC are far from well constrained due to high land surface heterogeneity,complicated mechanisms,and multiple influencing factors.Here,we use a process-based agroecosystem model(DLEM-Ag)in combination with diverse spatially-explicit gridded environmental data to quantify the long-term trend of SOC storage in global cropland area during 1901-2010 and identify the relative impacts of climate change,elevated CO2,nitrogen deposition,land cover change,and land management practices such as nitrogen fertilizer use and irrigation.Model results show that the total SOC and SOC density in the 2000s increased by 125%and 48.8%,respectively,compared to the early 20th century.This SOC increase was primarily attributed to cropland expansion and nitrogen fertilizer use.Factorial analysis suggests that climate change reduced approximately 3.2%(or 2,166 Tg C)of the total SOC over the past 110 years.Our results indicate that croplands have a large potential to sequester C through implementing better land use management practices,which may partially offset SOC loss caused by climate change.

Fabrication of solid CH-CD multilayer microspheres for inertial confinement fusion

Deuterated polymer microspheres can be used as a neutron source in conjunction with lasers because thermonuclear fusion neutrons can be produced efficiently by collisions of the resulting energetic deuterium ions.A new type of solid deuterated polymer microsphere with a carbon hydrogen–carbon deuterium(CH-CD)multilayer has been designed for preparing the target for inertial confinement fusion(ICF)experiments.To fabricate these solid CH-CD multilayer microspheres,CH beads are first fabricated by a microfluidic technique,and the CD coating layer is prepared by a plasma polymerization method.Both polystyrene(PS)and poly(α-methylstyrene)(PAMS)are used as the material sources for the CH beads.The effects of the PS and PAMS materials on the quality of the solid CH beads and the resulting CH-CD multilayer polymer microspheres are investigated.The solid PS beads have better sphericity and a smoother surface,but large vacuoles are observed in solid PS-CD multilayer microspheres owing to the presence of residual fluorobenzene in the beads and a glass transition temperature of the solid PS beads that is lower than the temperature of plasma polymerization.Therefore,solidPAMSbeads are more suitable as a mandrel for fabricating solid CH-CD multilayer polymer microspheres.Solid CH-CD multilayer microspheres with specified size have been successfully prepared by controlling the droplet size and the CD deposition rate and deposition time.Compared with the design value,the diameter deviation of the inner CH beads and the thickness deviation of the CD layer can be controlled within 20μmand 2μm,respectively.Thus,an approach has been developed to fabricate solid CH-CD multilayer microspheres that meet the physical design requirements for ICF.

Progress and challenges in the fabrication of DPS shells for ICF

To improve the quality of deuterated polystyrene(DPS)shells,the synthesis and purification of DPS as well as the fabrication of DPS shells are investigated.The molecular weight and molecular weight distribution,measured by GPC-MALLS,are about 350 kg mol^(-1) and less than 2.0,respectively.The results of TG and GC-MS indicate that the residual solvent is almost completely removed.DPS shells with;300 mm–2500 mmdiameter and;10 mm–100mmwall thickness are successfully prepared by a microfluidic device.The monodispersity of the diameter ismuchbetter than that of the wall thickness in a batch ofDPSshells.The vacuoles can be suppressed by both reducing hydrophilic residues in DPS and adding some salts into the outer water phase(W2).The defects appearing during the drying process decrease by heat treatment,ethanol exchange,and lowered drying temperature.The results presented in this work not only provide guidelines for the preparation of DPS shells of better quality,but also indicate challenges for the future.

Interannual evolution of the chemical composition,sources and processes of PM_(2.5)in Chengdu,China:Insights from observations in four winters

The air quality in China has improved significantly in the last decade and,correspondingly,the characteristics of PM_(2.5)have also changed.We studied the interannual variation of PM_(2.5)in Chengdu,one of the most heavily polluted megacities in southwest China,during the most polluted season(winter).Our results show that the mass concentrations of PM_(2.5)decreased significantly year-by-year,from 195.8±91.0μg/m~3in winter 2016 to 96.1±39.3μg/m^(3)in winter 2020.The mass concentrations of organic matter(OM),SO_()4^(2-),NH_(4)^(+)and NO_(3)^(-)decreased by 49.6%,57.1%,49.7% and 28.7%,respectively.The differential reduction in the concentrations of chemical components increased the contributions from secondary organic carbon and NO_(3)^(-)and there was a larger contribution from mobile sources.The contribution of OM and NO_(3)^(-)not only increased with increasing levels of pollution,but also increased year-by-year at the same level of pollution.Four sources of PM_(2.5)were identified:combustion sources,vehicular emissions,dust and secondary aerosols.Secondary aerosols made the highest contribution and increased year-by-year,from 40.6%in winter 2016 to 46.3% in winter 2020.By contrast,the contribution from combustion sources decreased from 14.4% to 8.7%.Our results show the effectiveness of earlier pollution reduction policies and emphasizes that priority should be given to key pollutants(e.g.,OM and NO_(3)^(-))and sources(secondary aerosols and vehicular emissions)in future policies for the reduction of pollution in Chengdu during the winter months.

Self-driven directional dehydration enabled eco-friendly manufacture of chrome-free leather

Manufacture of eco-friendly chrome-free leather is of great significance for realizing sustainable development of leather industry.Conventional tanning theory believes that it is impossible to convert raw hide to leather without the utilization of cross-linking agent(e.g.,chrome salts)among collagen fibers in raw hide.Here,we developed a brand-new leather manufacture strategy that relied on the composite dehydration media enabled self-driven directional dehydration mechanism to accomplish chrome-free leather manufacture for the first time,rather than followed the classic cross-linking mechanism that has been obeyed for more than one century in leather industry.We demonstrated that the essence of leather making is to regulate the water content in raw hide rather than to form cross-linkage among collagen fibers.The composite dehydration media comprised of anhydrous ethanol and molecular sieves(3A activated zeolite powder)successfully guaranteed continuous self-driven directional dehydration of raw hide by establishing stable water concentration gradient between raw hide and ethanol,which significantly increased the dispersity of collagen fibers in raw hide(with the water content reduced from 56.07%to 5.20%),thus obtaining chrome-free leather that is more ecological than chrome-tanned leather due to the elimination of any tanning agent.The as-prepared chrome-free leather exhibited outstanding tear force(174.86 N),tensile strength(24.56 N mm−2),elongation at break(53.28%)and dry-thermal stability,superior to chrome-tanned leather.Notably,the used compos-ite dehydration media was recyclable for chrome-free leather manufacture,therefore facilitating an environmentally benign leather manufacture process.Our investigations are expected to open up a new conceptual leather making strategy that is applicable for realizing substantial manufacture of eco-friendly leather.