聚合物及其混合物的太赫兹介电性质测定与分析方法

聚合物材料因其对太赫兹波的高透过率以及良好的塑形能力在太赫兹研究中扮演了重要的角色,由于材料的介电特性直接关系着折射率、极化率等重要性质,不同的应用场合通常需要材料呈现出特殊的太赫兹介电响应,一方面可以选取不同的聚合物材料,另一方面可以通过多种聚合物的混合实现材料介电性质的调制。聚合物材料合理的选取和设计建立在材料太赫兹介电精确表征之上,然而利用太赫兹时域光谱系统(THz-TDS)对聚合物材料进行透射式太赫兹介电表征时,材料内部空气孔隙的存在会影响表征结果的复现性,同时也会影响共混聚合物介电性质的分析和预测。因此以Landau, Lifshitz, Looyenga(LLL)模型为基础提出了考虑空气影响的介电分析模型,并选取了在太赫兹研究中广泛使用的聚合物材料聚乙烯(PE)和聚四氟乙烯(PTFE)对模型的有效性和稳定性加以验证,展开了两种材料单质和混合物两方面的介电分析。在太赫兹波透射样品之后的相位变化信息中提取出样品的介电常数,同一种物质制备的样片间太赫兹介电谱存在明显差异,使用包含气隙影响的LLL模型处理实验数据后,样品介电常数中空气的介电影响被移除,从而得到了两种材料的本征介电常数,在此基础上,使用测得的本征介电常数和混合物样品中两种材料的体积占比信息代入包含气隙影响的LLL模型计算得到了不同配比混合物的太赫兹介电常数的模拟值,并与THz-TDS实验获取的实验值进行了对比。利用所提出的有效介质模型,聚乙烯和聚四氟乙烯在10～40 cm-1波段内移除空气影响后的平均介电常数为2.315±0.003（±0.13%）和2.109±0.003（±0.14%）,在不同重量、不同厚度的单组份样品间模型测定的聚合物介电常数保持了良好的重复性,在对混合物的太赫兹介电性质测定与分析中,利用模型计算的混合物介电常数模拟值与THz-TDS测定的介电常数实验值保持了高度线性相关,其相关系数为0.964 3,全局相对误差为1.08%,体现了模型的可靠性。提出的介电分析模型可以扩展到更多的高分子材料单质及其混合物的太赫兹介电性质表征中,对太赫兹波段的共混聚合物材料设计具有参考价值。     

Nonlinear force density method for the form-finding of minimal surface membrane structures

We develop an alternative approach for the form-finding of the minimal surface membranes (including cable membranes) using discrete models and nonlinear force density method. Two directed weighted graphs with 3 and 4-sided regional cycles, corresponding to triangular and quadrilateral finite element meshes are introduced as computational models for the form-finding problem. The triangular graph model is closely related to the triangular computational models available in the literature whilst the quadrilateral graph uses a novel averaging approach for the form-finding of membrane structures within the context of nonlinear force density method. The viability of the mentioned discrete models for form-finding are studied through two solution methods including a fixed-point iteration method and the Newton–Raphson method with backtracking. We suggest a hybrid version of these methods as an effective solution strategy. Examples of the formation of certain well-known minimal surfaces are presented whilst the results obtained are compared and contrasted with analytical solutions in order to verify the accuracy and viability of the suggested methods.     

Miniaturized Salinity Gradient Energy Harvesting Devices

Harvesting salinity gradient energy, also known as “osmotic energy” or “blue energy”, generated from the free energy mixing of seawater and fresh river water provides a renewable and sustainable alternative for circumventing the recent upsurge in global energy consumption. The osmotic pressure resulting from mixing water streams with different salinities can be converted into electrical energy driven by a potential difference or ionic gradients. Reversed-electrodialysis (RED) has become more prominent among the conventional membrane-based separation methodologies due to its higher energy efficiency and lesser susceptibility to membrane fouling than pressure-retarded osmosis (PRO). However, the ion-exchange membranes used for RED systems often encounter limitations while adapting to a real-world system due to their limited pore sizes and internal resistance. The worldwide demand for clean energy production has reinvigorated the interest in salinity gradient energy conversion. In addition to the large energy conversion devices, the miniaturized devices used for powering a portable or wearable micro-device have attracted much attention. This review provides insights into developing miniaturized salinity gradient energy harvesting devices and recent advances in the membranes designed for optimized osmotic power extraction. Furthermore, we present various applications utilizing the salinity gradient energy conversion.     

Silver(I) ion induced formation of 2-D ternary lead(II)-silver(I)-4-tolythiolate [PbAg2(μ-Stol)2(μ4-Stol)2]n from 1-D binary lead(II)-4-tolythiolate [(μ-Cl)Pb2(Stol)(μ-Stol)2]n (tol = 4-tolyl)

Treatment of [Pb(Stol)₂]_n with an equiv of [Et₄N]Cl in DMF afforded a new 1-D polymeric complex, [(μ-Cl)Pb₂(Stol)(μ-Stol)₂]_n (1), with Pb–Cl–Pb links. Interaction of 1 with a suspension of [Ag(Stol)] in DMF resulted in formation of a 2-D polymeric complex, [PbAg₂(μ-Stol)₂(μ₄-Stol)₂]_n (2), with the planar four-membered Ag₂S₂ and PbAgS₂ rings bridged by μ-Stol and μ₄-Stol ligands. Both polymeric complexes were structurally characterized by single-crystal X-ray diffraction analysis.     

Properties and performance of BaxSr1−xCo0.8Fe0.2O3−δ materials for oxygen transport membranes

The present paper discusses the oxygen transport properties, oxygen stoichiometry, phase stability, and chemical and mechanical stability of the perovskites (BSCF) and (SCF) for air separation applications. The low oxygen conductive brownmillerite phase in SCF is characterized using in-situ neutron diffraction, thermographic analysis and temperature programmed desorption but this phase is not present for BSCF under the conditions studied. Although both materials show oxygen fluxes well above 10 ml/cm²·min at T=1,273 K and pO₂=1 bar for self-supporting, 200 μm-thick membranes, BSCF is preferred as a membrane material due to its phase stability. However, BSCF’s long-term stable performance remains to be confirmed. The deviation from ideal oxygen stoichiometry for both materials is high: δ>0.6. The thermal expansion coefficients of BSCF and SCF are 24×10⁻⁶ and 30×10⁻⁶ K⁻¹, respectively, as determined from neutron diffraction data. The phenomenon of kinetic demixing has been observed at pO₂<10⁻⁵ bar, resulting in roughening of the surface and enrichment with alkaline earth metals. Stress–strain curves were determined and indicated creep behavior that induces undesired ductility at T=1,073 K for SCF. Remedies for mechanical and chemical instabilities are discussed.     

Preparation and characterization of mono-valent ion selective polypyrrole composite ion-exchange membranes

Polypyrrole composite cation- and anion-exchange membranes (CEM and AEM), in which polypyrrole (PPY) coated on one surface of the membrane as a thin layer, were prepared by chemical polymerization of pyrrole in the presence of high oxidant concentration (Na₂S₂O₈). Existence of polypyrrole layer on the both types of ion-exchange membranes were confirmed by recording their coating density, SEM images and conductivity. These membranes were extensively characterized by recording their properties such as water uptake, ion-exchange capacity, contact angle, permselectivity and membrane conductivity as a function of polymerization time such as. It was observed that due to coating of PPY for 2 h, membrane permselectivity of CEM for NaCl (0.907) was reduced to 0.873, while it was increased from 0.747 to 0.889 in the case of AEM. Similar behaviors were also obtained for bi-valent electrolytes. Electrodialysis experiments were also conducted with polypyrrole composite ion-exchange membranes using mixed electrolytic systems. Relative dialytic rates for NaCl with respect to other bi-valent electrolyte were varied in between 5 and 8 (depending on bi-valent electrolyte), which suggested the feasible and efficient separation of mono-valent from bi-valent electrolyte. Slower electro-migration of bi-valent electrolyte (CaCl₂, MgCl₂ and CuCl₂) in comparison to NaCl was explained on the basis of synergetic effect of sieving of bulkier bi-valent cations by tight and rigid polypyrrole layer and the difference in electrostatic and hydrophobic–hydrophilic repulsion force between bi-valent cations and mono-valent cation. It was concluded that these composite membranes are suitable for the efficient separation of same type of charged ions by electro-driven separation techniques.     

Hydrogen Production by Water Dissociation in Surface‐Modified BaCoxFeyZr1−x−yO3−δ Hollow‐Fiber Membrane Reactor with Improved Oxygen Permeation

A porous perovskite BaCo_xFe_yZr_0.9?x?yPd_0.1O_3?δ (BCFZ‐Pd) coating was deposited onto the outer surface of a BaCo_xFe_yZr_1?x?yO_3?δ (BCFZ) perovskite hollow‐fiber membrane. The surface morphology of the modified BCFZ fiber was characterized by scanning electron microscopy (SEM), indicating the formation of a BCFZ‐Pd porous layer on the outer surface of a dense BCFZ hollow‐fiber membrane. The oxygen permeation flux of the BCFZ membrane with a BCFZ‐Pd porous layer increased 3.5 times more than that of the blank BCFZ membrane when feeding reactive CH₄ onto the permeation side of the membrane. The blank BCFZ membrane and surface‐modified BCFZ membrane were used as reactors to shift the equilibrium of thermal water dissociation for hydrogen production because they allow the selective removal of the produced oxygen from the water dissociation system. It was found that the hydrogen production rate increased from 0.7 to 2.1 mL H₂ min^?1 cm^?2 at 950 °C after depositing a BCFZ‐Pd porous layer onto the BCFZ membrane.     

A highly efficient capillary electrophoresis-based method for size determination of water-soluble CdSe/ZnS core-shell quantum dots

This paper describes a highly efficient method for size determination of water-soluble CdSe/ZnS core-shell quantum dots (QDs) by capillary electrophoresis (CE) using polymer additive as sieving medium. The influence of some factors, such as kinds and concentrations of the sieving medium, pH, concentrations of the background electrolyte (BGE) and applied voltage, on the separation of QDs was investigated. Under the optimal separation conditions, four different sized QDs were successfully separated, and the relative standard deviation (RSD) of the migration times for these QDs was below 1.013%. In addition, an equation was fit by taking into account the correlation existing between the electrophoretic mobilities and the sizes of a set of QDs. The feasibility of this equation to measure the sizes of other QDs was confirmed by comparison with the sizes obtained by transmission electron microscopy (TEM) experiment. This work offers a novel method for size determination of QDs, and provides an important reference on the study of QDs based on CE.     

Folate-targeted optical and magnetic resonance dualmodality PCL-<Emphasis Type="Italic">b</Emphasis>-PEG micelles for tumor imaging

A biodegradable tumor targeting nano-probe based on poly（ε-caprolactone）-b-poly（ethylene glycol）block copolymer（PCL-b-PEG）micelle functionalized with a magnetic resonance imaging（MRI）contrast agent diethylenetriaminepentaacetic acid-gadolinium(DTPA-Gd³⁺)on the shell and a near-infrared（NIR）dye in the core for magnetic resonance and optical dual-modality imaging was prepared.The longitudinal relaxivity（r₁）of the PCL-b-PEG-DTPA -Gd³⁺micelle was 13.4（mmol/L）^-1s^-1,three folds of that of DTPA-Gd³⁺,and higher than that of many polymeric contrast agents with similar structures.The in vivo optical imaging of a nude mouse bearing xenografted breast tumor showed that the dual-modality micelle preferentially accumulated in the tumor via the folic acid-mediated active targeting and the passive accumulation by the enhanced permeability and retention（EPR）effect.The results indicated that the dualmodality micelle is a promising nano-probe for cancer detection and diagnosis.