Thermal conductivity analysis using three‐dimensional microstructures of gelation freezing derived cellular mullite

The relationship between thermal conductivity and unidirectional cellular mullite microstructures created with the freeze casting route is discussed using actual three‐dimensional (3D) images, in which a homogenization method was conducted with microscopic models created from 3D images, the temperature variation in macroscopic models by the finite element method (FEM), and local heat conduction in microscopic models. The simulation results were consistent with the experimental results. This image‐based modeling technique was thus confirmed to be a strong tool for the prediction of various thermal properties of porous ceramics.     

A multifunctional ribonuclease A-conjugated carbon dot cluster nanosystem for synchronous cancer imaging and therapy

Carbon dots exhibit great potential in applications such as molecular imaging and in vivo molecular tracking. However, how to enhance fluorescence intensity of carbon dots has become a great challenge. Herein, we report for the first time a new strategy to synthesize fluorescent carbon dots (C-dots) with high quantum yields by using ribonuclease A (RNase A) as a biomolecular templating agent under microwave irradiation. The synthesized RNase A-conjugated carbon dots (RNase A@C-dots) exhibited quantum yields of 24.20%. The fluorescent color of the RNase A@C-dots can easily be adjusted by varying the microwave reaction time and microwave power. Moreover, the emission wavelength and intensity of RNase A@C-dots displayed a marked excitation wavelength-dependent character. As the excitation wavelength alters from 300 to 500 nm, the photoluminescence (PL) peak exhibits gradually redshifts from 450 to 550 nm, and the intensity reaches its maximum at an excitation wavelength of 380 nm. Its Stokes shift is about 80 nm. Notably, the PL intensity is gradually decreasing as the pH increases, almost linearly dependent, and it reaches the maximum at a pH = 2 condition; the emission peaks also show clearly a redshift, which may be caused by the high activity and perfective dispersion of RNase A in a lower pH solution. In high pH solution, RNase A tends to form RNase A warped carbon dot nanoclusters. Cell imaging confirmed that the RNase A@C-dots could enter into the cytoplasm through cell endocytosis. 3D confocal imaging and transmission electron microscopy observation confirmed partial RNase A@C-dots located inside the nucleus. MTT and real-time cell electronic sensing (RT-CES) analysis showed that the RNase A@C-dots could effectively inhibit the growth of MGC-803 cells. Intra-tumor injection test of RNase A@C-dots showed that RNase A@C-dots could be used for imaging in vivo gastric cancer cells. In conclusion, the as-prepared RNase A@C-dots are suitable for simultaneous therapy and in vivo fluorescence imaging of nude mice loaded with gastric cancer or other tumors.     

Comparative Hydrodynamic Analysis of Narrow and Pilot‐Scale Bubble Columns with Internals

For a stable operation of exothermic processes in bubble column reactors, an appropriate heat control is required, e.g., through dense internal tube bundle heat exchangers. Their impact on hydrodynamic characteristics and scaling approaches is studied for columns of different scales. Two different column dimensions (DN100 and DN400) were equipped with two common tube patterns of triangular and square pitches to study local fluid dynamics. Based on geometrical tube bundle scaling quantities, hydrodynamic similarity as a scale‐up criterion with respect to average holdups, phase distributions, and local gas structures can be reached.     

γ-巯丙基三乙氧基硅烷水解程度对纳米二氧化硅接枝机理影响的DFT研究

为探索γ-巯丙基三乙氧基硅烷(MPTS)水解程度对纳米二氧化硅接枝机理的影响，采用基于密度泛函理论(DFT)的量子化学方法，选择合适的泛函和合理的模型，系统研究了MPTS及其不同水解程度产物的反应活性及与纳米二氧化硅的接枝机理，为纳米二氧化硅改性工艺优化及改性效果的提升提供重要理论基础。结果表明：经数据对比确定GGA-PBE泛函优化后的纳米二氧化硅团簇模型为最合理模型。二氧化硅表面硅羟基中的氧原子为亲核活性中心，氢原子为亲电活性中心，MPTS及其水解产物中氧原子为亲核活性中心，硅原子为亲电活性中心。水解引起LUMO轨道向硅原子偏移，硅原子亲电指数提高，而HOMO轨道向氧原子偏移，氧原子的亲核指数提高，引起MPTS水解产物更容易受到二氧化硅表面硅羟基攻击，进而提高了接枝反应活性。MPTS的水解降低了接枝反应的活化能，不同水解程度产物接枝反应活化能(E _a)顺序为M0＞M3＞M1＞M2(M0、M1、M2和M3分别表示MPTS及其一级、二级和三级水解产物)，接枝反应属于S_N2亲核取代，且为放热反应。M0、M1和M2都是通过脱醇机理发生接枝反应，空间位阻效应和偶联剂中心硅原子的亲电性能为反应主要控制因素，而M3是通过脱水机理发生接枝反应。     

γ射线法测量高压管束间气液两相流的截面含气率分布

在立式蒸汽发生器垂直管束间的气液两相流中，截面含气率是其中一个重要参数。使用γ射线法对高温高压下垂直管束间气液两相流截面含气率的分布规律进行了实验研究。实验压力分别为5、7、9 MPa，质量流速为300 kg/(m²?s)，热力学干度的范围为0.003 ~ 0.4。实验得到了垂直管束间截面含气率随热力学干度、体积含气率和压力的变化关系；并与经典公式的计算结果对比发现，在低干度区域，实验结果与Miropolskii模型、Smith模型和Armand模型偏差较大，均大于30%，在高干度区域偏差较小；基于Armand理论，通过多元线性回归法拟合出本文工况下平均截面含气率的计算关联式，与日本核动力工程公司(NUPEC)的实验数据偏差小于15%。本研究对蒸汽发生器的结构设计和流动特性研究具有重要意义。     

2,3-Dimethyl-2,3-diphenylbutane mediated grafting of vinyltriethoxysilane to polyethylene: a novel radical initiation system

The melt grafting of vinyltriethoxysilane (VTEOS) to polyethylene using 2,3-dimethyl-2,3-diphenylbutane (bicumene) as a radical initiator is demonstrated and compared to conventional peroxide-initiated processes. A bicumene-initiated modification of high density polyethylene at 290 °C provided no benefits in terms of selectivity when compared to a standard peroxide-based process operating at 180 °C. However, the selectivity of linear low-density polyethylene modification was influenced by chain scission, which counteracted the molecular weight effects of macroradical combination. Reactive extrusion data as well as studies of bicumene decomposition kinetics suggest that initiation occurs through an auto-oxidation mechanism that is facilitated by the interaction of cumyl radicals with oxygen.     

Grafting of poly(ethylene-block-ethylene oxide) onto a vapor grown carbon fiber surface by γ-ray radiation grafting

To modify the surface of vapor grown carbon fiber (VGCF), poly(ethylene-block-ethylene oxide) (PE-b-PEO, M_n=1400, PEO content=50 wt%) was successfully grafted onto the surface by using γ-ray irradiation of the PE-b-PEO-adsorbed VGCF in solvent-free system. It is found that the percentage of polymer grafting reached 15.0% when the PE-b-PEO-adsorbed VGCF was irradiated by γ-ray over 40 kGy dose at 110 °C, but at the lower irradiation temperature of 75 °C, the grafting reaction scarcely proceeded. This indicates that polymer radicals formed by γ-ray irradiation were successfully trapped by VGCF surface above melting point of PE-b-PEO. On the other hand, when the dispersion of VGCF in THF solution of PE-b-PEO was irradiated, the percentage of PE-b-PEO grafting was less than 4.0%. It was confirmed by a field-emission scanning electron microscope (FE-SEM) that the surface of the VGCF was uniformly covered by grafted PE-b-PEO. In addition, the surface free energy of ungrafted and PE-b-PEO-grafted VGCF was determined.     

Preparation of a mono‐sheet bipolar membrane by simultaneous irradiation grafting polymerization of acrylic acid and chloromethylstyrene

A new type of mono‐sheet bipolar membrane was produced from a porous polyethylene (PE) substrate using simultaneous irradiation grafting polymerization of acrylic acid (AA) on one side and chloromethylstyrene (CMS) on the other side. PE film with absorbent filter paper absorbing AA on one side and paper absorbing CMS on the other side was irradiated in the cobalt‐60 gamma ray irradiation field, followed by quaternization with trimethylamine aqueous solution. AA and CMS were grafted on the substrate membrane simultaneously. The performance of the final membrane is significantly affected by the irradiation time. For short irradiation time, the prepared membrane behaves as a bipolar membrane; whereas for long irradiation time, the final membrane behaves as a charge mosaic membrane. Therefore, by controlling the conditions, a bipolar membrane with good current rectification can be prepared, across which the voltage drop is ～2.0 V at the current density 800 A/m² in 1.0 M NaOH. This preparation method is simple and can be applied both in laboratory and in industry. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 572–576, 2003     

Self‐assembling metal coatings from phosphated and siloxane‐modified polyurethane dispersions: An analysis of the coating–air interface

Polyurethane dispersion coatings containing phosphate and siloxane chains were evaluated for their self‐assembling properties for a single‐coating system. Dynamic contact angles (DCAs) and X‐ray photoelectron spectroscopy (XPS) were used to study the coating–air interface. The siloxane chains were the predominant species on the surfaces of the coatings. The wetting properties of the coating–air interface were reversed when the coated panels were immersed in an ionic solution, and the decrease in hydrophobicity was linear with time. Results from XPS and DCA analyses were similar. The self‐assembling properties of the coatings could be useful in the development of hydrophobic coatings from hydrophilic polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 893–899, 2003     

Ion irradiation effect on spark plasma sintered silicon carbide ceramics with nanostructured ferritic alloy aid

Silicon carbide (SiC) is a promising material with excellent chemical and physical performance under irradiation for advanced nuclear applications. The addition of nanostructured ferritic alloy (NFA) has been proven beneficial for the densification of SiC ceramics based on our previous work. To understand their microstructural evolution and irradiation resistance, spark plasma sintered (SPSed) SiC ceramics with and without NFA aid (0 vol% NFA‐100 vol% SiC, 2.5 vol% NFA‐97.5 vol% SiC, and 5 vol% NFA‐95 vol% SiC) were exposed to 5 MeV Si⁺⁺ irradiation. The ion irradiation strongly modifies the surface morphology with isolated sand dune shaped structures, which can be explained by the Bradley‐Harper (B‐H) theory. SRIM simulation for both the pure SiC and NFA‐SiC predicts similar surface damage of ~45 dpa and peak damage of ~790 dpa at ~2.0 μm depth. For the actual samples, the SiC matrix is completely amorphous up to ~2.2 μm thickness (from the surface dune valley to the amorphous layer boundary), which is consistent with the SRIM predicted depth of ~2.3 μm. Reaction product (Fe,Cr)₃Si in the NFA‐SiC samples maintains a crystalline structure with dislocation loops. A defect rate model is applied to understand the fundamental difference in ion irradiation resistance between SiC and (Fe,Cr)₃Si.