Aqueous-phase exfoliation of graphite in the presence of polyvinylpyrrolidone for the production of water-soluble graphenes

Treatment of crystalline graphite fine powder with an aqueous solution of the harmless and versatile substance polyvinylpyrrolidone under sonication results in water-soluble, polymer-protected graphene single layers without oxidation or destruction of the sp² character of the carbon core. The liquid-phase extraction of graphene monolayers was evidenced by TEM and AFM techniques, while their graphitic character was checked with Raman spectroscopy. Besides PVP, the water-soluble biopolymers albumin and sodic carboxymethylcellulose were also employed successfully in the aqueous-phase exfoliation of graphite, thereby supporting the generic character of the present method using a variety of suitable polymeric extractants.     

传热传质分离的绝热吸收过程实验研究

根据传热传质分离的吸收形式,设计加工了一台溴化锂绝热降膜吸收的实验装置,对溴化锂水溶液在倾斜平板上对水蒸气的吸收特性进行了实验研究,分析了预冷却温差、溶液流量及平板倾角对吸收过程的影响。实验结果表明:预冷却温差、溶液流量及平板倾角越大,溴化锂溶液对水蒸气的吸收效果越好,并认为吸收过程可以分成三个步骤,另外就热质分离吸收器的设计过程中的溴化锂溶液的最小速度提出建议。     

An extension of the SIMPLE based discontinuous Galerkin solver to unsteady incompressible flows

In this paper, we present a SIMPLE based algorithm in the context of the discontinuous Galerkin method for unsteady incompressible flows. Time discretization is done fully implicit using backward differentiation formulae (BDF) of varying order from 1 to 4. We show that the original equation for the pressure correction can be modified by using an equivalent operator stemming from the symmetric interior penalty (SIP) method leading to a reduced stencil size. To assess the accuracy as well as the stability and the performance of the scheme, three different test cases are carried out: the Taylor vortex flow, the Orr‐Sommerfeld stability problem for plane Poiseuille flow and the flow past a square cylinder. (1) Simulating the Taylor vortex flow, we verify the temporal accuracy for the different BDF schemes. Using the mixed‐order formulation, a spatial convergence study yields convergence rates of k + 1 and k in the L²‐norm for velocity and pressure, respectively. For the equal‐order formulation, we obtain approximately the same convergence rates, while the absolute error is smaller. (2) The stability of our method is examined by simulating the Orr–Sommerfeld stability problem. Using the mixed‐order formulation and adjusting the penalty parameter of the symmetric interior penalty method for the discretization of the viscous part, we can demonstrate the long‐term stability of the algorithm. Using pressure stabilization the equal‐order formulation is stable without changing the penalty parameter. (3) Finally, the results for the flow past a square cylinder show excellent agreement with numerical reference solutions as well as experiments. Copyright © 2015 John Wiley & Sons, Ltd.     

Fabrication and room-temperature exciton photoluminescence stability studies of inorganic–organic hybrid (C12H25NH3)2SnI4 thin films

A new methodology has been developed to fabricate the thin films of Tin (II) iodide based inorganic–organic (IO) hybrid, (C₁₂H₂₅NH₃)₂SnI₄, from direct and cost-effective three-step processing. The fabrication is based on room-temperature electrochemical deposition followed by simple solution processing. These IO hybrid films show room-temperature exciton related photoluminescence at 616 nm due to quantum and dielectric confinement effects. Systematic X-ray diffraction and optical studies are performed to understand the structural modification due to oxidation and consequent emission degradation. Post-processing methods to avoid emission degradation are also been demonstrated. The simple solution processing methodology and unique highly red-emitting IO hybrids, would be of interest for many multi-functional optoelectronic applications.     

Gram determinant solutions to nonlocal integrable discrete nonlinear Schrödinger equations via the pair reduction

In this paper, Gram determinant solutions of local and nonlocal integrable discrete nonlinear Schrödinger (IDNLS) equations are studied via the pair reduction. A generalized IDNLS equation is firstly introduced which possesses the single Casorati determinant solution. Two kinds of Gram determinant solutions are presented from Casorati determinant ones due to the gauge freedom. The different pair constraint conditions for wave numbers are imposed and then solutions of local and nonlocal IDNLS equations are derived in terms of Gram determinant.     

Branched polyacrylamides: Synthesis and effect of molecular architecture on solution rheology

Linear, star and comb-like polyacrylamides (PAM) have been prepared by atomic transfer radical polymerization (ATRP) in aqueous media at room temperature. The influence of the molecular architecture of PAM on the rheological properties in aqueous solution has been investigated. The well-known theory of increased entanglement density by branching for polymers in the melt can also be applied to polymers in the semi-dilute water solutions. We have demonstrated this by investigating the rheological properties of PAM of similar molecular weights with different molecular architectures. Interestingly, the solution viscosity of a comb PAM is higher compared to its linear and star analogues (both at equal span molecular weight, M_n,SPAN, and total molecular weight, M_n,tot). In addition to the pure viscosity, we also demonstrate that the visco-elastic properties of the polymeric solutions depend significantly on the molecular architecture of the employed PAM. The elastic response of water solutions containing comb PAM is more pronounced than for solutions containing either linear or star PAM at similar M_n,SPAN and M_n,tot. The obtained results pave the way for application of these polymeric materials in Enhanced Oil Recovery (EOR).     

Small asymmetric anthracene–thiophene compounds as organic thin-film transistors

Anthracene and thiophene compounds are promising materials for OTFTs. We report here, the synthesis, as well as the physical, thermal, and optoelectronic properties of alkyl-substituted asymmetric anthracene–thiophene compounds connected by a bridged triple bond. The target molecules were synthesized using 2-bromoanthracene as the starting material, and the proceeding reactions included alkylation, bromination, and the Sonogashira coupling reaction. The synthesized compounds were both thermally and electrochemically stable. Among the synthesized compounds, HTEA (7a) and DTEA (7b) showed mobility and on/off ratio values of 1.3×10⁻¹ cm²/V s, 2.6×10⁶ and 2.0×10⁻² cm²/V s, 1.0×10⁶, respectively.     

胶束电动色谱法测定五维他口服溶液中维生素B_1、B_2、B_6、烟酰胺、泛酸钙与苯甲酸钠

建立了胶束电动色谱(MEKC)法通过波长切换同时测定五维他口服溶液中的维生素B_1、B_2、B_6、烟酰胺、泛酸钙及苯甲酸钠含量的方法,并优化了检测波长、十二烷基硫酸钠(SDS)的浓度、分离电压、缓冲液浓度及pH值等实验条件。最佳分离条件为以未涂渍的标准熔融石英毛细管柱(75μm×50 cm,有效长度42 cm)为分离通道;40 mmol/L硼酸+40 mmol/L硼砂+20 mmol/L SDS(pH 9.0)为运行缓冲液,分离电压20 kV,柱温25℃,检测波长为270 nm(维生素B_1、B_2、B_6、烟酰胺及苯甲酸钠)和200 nm(泛酸钙),电动进样10 kV、进样时间10 s。结果显示,6种化合物可在13 min内实现基线分离,且在一定质量浓度范围内线性良好,相关系数(r)不小于0.998 9;3个加标水平下的平均回收率为97.0%～103%,RSD为0.60%～1.8%。该方法快速、准确,可用于五维他口服溶液中维生素B_1、B_2、B_6、烟酰胺、泛酸钙及苯甲酸钠的含量测定。     

Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4–NaCl–H2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization (FGD) gypsum. When purified FGD gypsum was used as raw material, the morphology and phase structure of the hydrothermal products grown in pure water, H₂SO₄–H₂O, NaCl–H₂O, and H₂SO₄–NaCl–H₂O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated. The results indicate that calcium sulfate whiskers grow favorably in the H₂SO₄–NaCl–H₂O system. When prepared using 10–70 g NaCl/kg gypsum −0.01 M H₂SO₄–H₂O at 130 °C for 60 min, the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 μm and lengths from 200 to 600 μm, and their phase structure was calcium sulfate hemihydrate (HH). Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed. With the co-presence of sulfuric acid and sodium chloride in the reaction solution, the concentrations of Ca²⁺ and SO₄²⁻ can be kept relatively stable, which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.