Polymer hollow particles with controllable holes in their surfaces

Colloidal particles with hollow interiors play important roles in microencapsulation-a process that has found widespread use in applications such as controlled release of drugs, cosmetics, inks, pigments or chemical reagents; protection of biologically active species; and removal of pollutants. The hollow particles are most commonly prepared by coating the surfaces of colloidal templates with thin layers of the desired material (or its precursor), followed by selective removal of the templates by means of calcination or chemical etching. This simple and straightforward approach works for a variety of materials that include polymers, ceramics, composites and metals. For polymers, methods such as emulsion polymerization, phase separation, crosslinking of micelles and self-assembly have also been demonstrated for generating hollow structures. However, diffusion through these closed shells with pores <10 nm is often a slow process. To solve this problem, macroporous capsules have been fabricated by organizing colloids around liquid droplets to form colloidosomes or by controlling the mixing of liquid droplets. Here we report the preparation of another class of macroporous capsules-polymer shells with controllable holes in their surfaces. After loading of functional materials, the holes can be closed by means of thermal annealing or solvent treatment.     

Loading and scheduling for flexible manufacturing systems with controllable processing times

This study addresses the problem of determining the allocation of operations and their tools to machines, the operation processing times and the allocation/sequence of the parts to be processed on each machine for flexible manufacturing systems with controllable processing times. Tool lives, tool copies and tool sharing are also considered. An integer programming model is developed for the objective of minimizing the sum of operation processing and tardiness costs. Then, iterative algorithms are proposed that solve the two subproblems iteratively, where the loading subproblem is solved by a modified bin packing algorithm under initial processing times and the resulting scheduling subproblem is solved by a priority scheduling method while modifying the loading plans and operation processing times iteratively. Computational experiments were carried out, and the results are reported.     

Fabrication of fritless chromatographic microchips packed with conventional reversed-phase silica particles

This paper describes the development and study of a disposable and inexpensive microfluidic chip, fabricated from poly(dimethylsiloxane) (PDMS) incorporating conventional chromatographic reversed-phase silica particles (C18) without the use of frits, permanent physical barriers, tapers, or restrictors. The packing of C18 modified silica particles into the microfluidic channels is made possible by the hydrophobic nature and excellent elasticity of PDMS. Keystone-, clamping-, and anchor-effects provide the stability and the compactness of the packing and attenuated wall-effects were observed.     

Thermal expansion behaviour of aluminum matrix composites with densely packed SiC particles

The coefficient of thermal expansion (CTE) of Al-based metal matrix composites containing 70 vol.% SiC particles (AlSiC) has been measured based on the length change from room temperature (RT) to 500 °C. In the present work, the instantaneous CTE(T) of AlSiC is studied by thermo-elastic models and micromechanical simulation using finite element analysis in order to explain abnormalities observed experimentally. The CTE(T) is predicted according to analytical thermo-elastic models of Kerner, Schapery and Turner. The CTE(T) is modelled for heating and cooling cycles from 20 °C to 500 °C considering the effects of microscopic voids and phase connectivity. The finite element analysis is based on a two-dimensional unit cell model comparing between generalized plane strain and plane stress formulations. The thermal expansion behaviour is strongly influenced by the presence of voids and confirms qualitatively that they cause the experimentally observed decrease of the CTE(T) above 250 °C.     

Highly controllable and green reduction of graphene oxide to flexible graphene film with high strength

Graphene film with high strength was fabricated by the assembly of graphene sheets derived from graphene oxide (GO) in an effective and environmentally friendly approach. Highly controllable reduction of GO to chemical converted graphene (CCG) was achieved with sodium citrate as a facile reductant, in which the reduction process was monitored by XRD analysis and UV–vis absorption spectra. Self-assembly of the as-made CCG sheets results in a flexible CCG film. This method may open an avenue to the easy and scalable preparation of graphene film with high strength which has promising potentials in many fields where strong, flexible and electrically conductive films are highly demanded.     

Batching and scheduling for a single-machine flexible machining cell with multi-fixturing pallets and controllable processing times

This study addresses an integrated batching and scheduling problem for a single-machine flexible machining cell in which each pallet can load multiple parts, i.e. multi-fixturing pallets, and part processing times can be changed with different processing costs, i.e. controllable processing times. The batching sub-problem is to select the set of parts to be produced in each period of a planning horizon and the resulting scheduling sub-problem is to determine the set of parts to be loaded on each multi-fixturing pallet, the part processing times and the pallet input/processing sequences for the parts selected in each period. A bi-criterion objective is considered that minimises the total tardiness and the total processing cost simultaneously. A solution approach is proposed that consists of three phases from the first to the last period: (a) generating the whole schedule over the planning horizon; (b) selecting the parts to be produced during the current period using the scheduling information; and (c) determining the final schedule for the selected parts. Simulation experiments were done on a number of test instances and the results are reported.     

Quantitative evaluation on wear resistance of aluminum alloy composites densely packed with SiC particles

Abstract

Wear behaviour was investigated for high volume fraction SiC particulate reinforced aluminum alloy composites by considering the shear stress acting on the specimen and the wear debris formed during sliding wear. The SEM morphology of worn subsurfaces showed that particles are fragmented, mechanically mixed, and then aligned in the wear direction caused by normal and tangential stresses. Wear debris were initially tiny lumps but finally delaminated due to the shear stress. A theoretical wear model was proposed for plastically deformable specimens worn by a rigid non-deformable steel ring by analysing the interspacing of SiC particles and the tangential stress applied to the worn surface. Predictions of this theoretical wear model were in good agreement with experimental results.     

Modeling of the mass-transfer kinetics in chromatographic columns packed with shell and pellicular particles

The equations of the general rate model of chromatography and those of simple models (the POR, equilibrium-dispersive, and transport-dispersive models) are derived for beds packed with shell particles. Shell particles are made of a solid, nonporous core surrounded by a shell of a porous material that has properties similar to those of the fully porous materials conventionally used in HPLC. These equations have no algebraic solutions, but the moments of the peaks eluted under linear conditions can be calculated, affording the HETP equation for these columns. The discussion of the contribution to the HETP of the mass-transfer resistances shows that shell particles exhibit much lower plate heights for large molecular size compounds (e.g., peptides and proteins) than do fully porous particles, this advantage increasing with decreasing thickness of the shell. In contrast, the efficiencies of columns packed with shell particles and with fully porous particles having the same diameters are nearly the same for low molecular weight compounds. In practice, the gain in efficiency due to the use of shell particles to separate high molecular weight compounds does not depend on the thickness of the shell provided that this thickness does not exceed 30-40% of the particle diameter. For larger thicknesses, it decreases with increasing thickness. Shell particles can also be used in preparative chromatography. For compounds that have a high internal mass-transfer resistance, the gain in efficiency compensates the reduction in sample capacity due to the lower volume of porous adsorbent. For proteins like BSA, the production rate could be doubled. The gain decreases with decreasing mass-transfer resistance, e.g., with decreasing molecular weight.     

A waveguide partially packed with superleak as a probe of superfluid properties

A waveguide partially packed with superleak and filled with superfluid ⁴ He is proposed as a useful configuration for studying acoustic modes. A calculation is performed indicating that the low-frequency propagating modes in such a system are of two types: a combined first/fourth sound mode and a modified second sound type mode. Experimentally, the waveguide is closed back on itself to form a toroidal resonator. Resonant frequencies were measured, and the experimental results compared favorably with the calculations. However, there remain unresolved discrepancies. This resonator may prove useful in measuring the possible superfluid properties of the new state of ³ He.     

In-depth characterization of slurry packed capillary columns with 1.0-microm nonporous particles using reversed-phase isocratic ultrahigh-pressure liquid chromatography

Fused-silica capillary columns packed with 1.0-microm nonporous C18 bonded particles are evaluated with isocratic ultrahigh-pressure liquid chromatography (UHPLC). Improved UHPLC techniques have demonstrated column efficiencies as high as 730 000 plates/m and run pressures over 6800 bar (100 000 psi) for packed 10-microm-inner diameter (i.d.) columns. Columns as large as 150 microm have been tested with UHPLC and show no flow-induced heating effects on separation efficiencies. van Deemter plot analysis for column i.d.s ranging from 10 to 150 microm shows an increase in column efficiency with a decrease in column i.d. Reduced parameter analysis further illustrates a decrease in reduced parameter A term and C term values with decreasing i.d. However, reduced parameter C term values for columns evaluated with UHPLC are an order of magnitude larger than C term values for larger particles at conventional pressures. Retention factors for moderately retained compounds are observed to increase with column i.d., suggesting an increase in packing density. Highly ordered packing arrangement at the column wall is seen for packed beds extruded from large-diameter columns.     

Synthesis of porous NiO nanocrystals with controllable surface area and their application as supercapacitor electrodes

We report a facile way to grow various porous NiO nanostructures including nanoslices, nanoplates, and nanocolumns, which show a structure-dependence in their specific charge capacitances. The formation of controllable porosity is due to the dehydration and re-crystallization of β-Ni(OH)₂ nanoplates synthesized by a hydrothermal process. Thermogravimetric analysis shows that the decomposition temperature of the β-Ni(OH)₂ nanostructures is related to their morphology. In electrochemical tests, the porous NiO nanostructures show stable cycling performance with retention of specific capacitance over 1000 cycles. Interestingly, the formation of nanocolumns by the stacking of β-Ni(OH)₂ nanoslices/plates favors the creation of small pores in the NiO nanocrystals obtained after annealing, and the surface area is over five times larger than that of NiO nanoslices and nanoplates. Consequently, the specific capacitance of the porous NiO nanocolumns (390 F/g) is significantly higher than that of the nanoslices (176 F/g) or nanoplates (285 F/g) at a discharge current of 5 A/g. This approach provides a clear illustration of the process-structure-property relationship in nanocrystal synthesis and potentially offers strategies to enhance the performance of supercapacitor electrodes.     

颗粒悬浮填料复合式膜生物反应器的过滤性能研究

介绍了颗粒填料复合式膜生物反应器(HMBR)在工业废水处理中的应用.在运行条件一致的情况下,对普通膜生物反应器(MBR)和颗粒填料复合式膜生物反应器(HMBR)进行了对比实验,着重研究了颗粒填料在膜污染控制方面的作用.结果表明:由于投加填料颗粒,HMBR的沉积层阻力减少了86%,临界通量增长了约20%;在长期运行过程中MBR的膜污染速率是HMBR的3.3倍.在膜生物反应器中投加颗粒填料可以有效地改善其过滤性能,减缓膜通量的下降.     

CuI-Si heterojunction solar cells with carbon nanotube films as flexible top-contact electrodes

We report the fabrication of CuI-Si heterojunction solar cells with carbon nanotubes (CNTs) as a transparent electrode. A flexible CNT network was transferred onto the top of a polycrystalline CuI layer, making a conformal coating with good contact with the underlying CuI. The solar cells showed power conversion efficiencies in the range of 6% to 10.5%, while the efficiency degradation was less than 10% after the device was stored in air for 8 days. Compared with conventional rigid electrodes such as indium tin oxide (ITO) glass, the flexibility of the CNT films ensures better contact with the active layers and removes the need for press-contact electrodes. Degraded cells can recover their original performance by acid doping of the CNT electrode. Our results suggest that CNT films are suitable electrical contacts for rough materials and structures with an uneven surface.      

Probability for the collision with a solid surface as a drop passes through a packed column

A method is proposed for determining the probability that a drop will collide with an element of a packed column. The cases of both ordered and disordered packings are treated. Experimental values of the probability are found for a packing of Raschig rings 25 x 25 mm in size.     

Free-standing flexible graphene-based aerogel film with high energy density as an electrode for supercapacitors

Two-dimensional graphene film exhibits sluggish ion diffusivity while three-dimensional(3D)graphene aerogel has low packing density and poor mechanical flexibility.Consequently,there is an urgent need for graphenebased film with both mechanical robustness and high specific capacitance.Here,we present an easy and scalable strategy for fabricating a free-standing flexible graphene-based aerogel film electrode with a two-layered structure,in which the top layer is an interconnected macroporous reduced graphene oxide/carbon nanotube(RGO/CNT)aerogel,and the bottom layer is a flexible electrospun polyacrylonitrile(PAN)nanofiber membrane.The porous 3D structure of the aerogel provides fast transport of electrolyte ions and electrons,while the nanofiber membrane provides both strong support for the aerogel and mechanical flexibility.Polypyrrole(PPy)can be uniformly loaded on RGO/CNT/PAN(RCP)composite aerogel film to provide pseudocapacitance,and nitrogen-doped RGO/CNT/carbon nanofiber(NRCC)aerogel film can be obtained by further pyrolysis.The resultant RCP@PPy-0.05//NRCC based asymmetric supercapacitor can have a maximum voltage of 1.7 V and a maximum energy density of 60.6 W h kg^-1at 850.2 W kg^-1.This indicates that free-standing graphene-based aerogel film can be used in flexible supercapacitors.     

基于PDMS纳米粒子改性的热模压技术

介绍了一种采用纳米SiO2、TiO2改性聚二甲基硅氧烷(PDMS)的方法,研究了两种纳米材料SiO2、TiO2添加的比例对热压效果的影响及优化条件,并分析了其改性后的热膨胀系数及杨氏模量的变化,以及其改性后热压效果的提高进行了初步分析,最后用改性的PDMS材料,快速成型来制造热压模具,热压制作聚甲基丙烯酸甲酯(PMMA)微流控芯片。与常用的金属模具(如镍模具)相比,此方法具有脱模容易,工艺周期短,难度低,重复性好,价格低等优点。     

Starch granules spot-coated with aluminum silicate particles and their use as fillers for papermaking

Mineral fillers are among the most important raw materials of paper. In papermaking, a filler is typically mixed as such with the fibrous stock prior to the forming section where it, together with the fibers and fines, forms a paper web with heterogeneous three-dimensional composite structure. The filler is eventually located both in the paper pores and between adjacent fibers. When light interacts with a multitude of solid-air interfaces occurring in such a structure, complicated light scattering effects take place. These effects are essential for appearance development, viz. brightness and opacity. Fillers contribute to these effects by increasing the number of such interfaces. Many fillers also cost significantly less than fibers. Therefore, it is advantageous to introduce as much filler as possible. It is also well known, however, that filler prevents formation of hydrogen bonding and is hence detrimental for strength development. In addition, the legislation of European Union favors increasing recovery of paper and packaging products, e.g., for energy production. However, as a side product of paper waste incineration, significant amounts of ash is formed. Hence it would be advantageous to replace inorganic fillers with combustible organic materials. We have fabricated a novel aluminum silicate spot-coated starch-based filler. The results indicate that when silicate is introduced in paper on the surface of starch granules benefits in light scattering and strength development can be achieved.     

Preparation and characterization of nanosized cobalt ferrite particles by co-precipitation method with citrate as chelating agent

Cobalt ferrite (CoFe₂O₄) nanoparticles were synthesized by a facile novel co-precipitation method with citrate as chelating agent. The synthesized cobalt ferrite nanoparticles were calcinated at 400, 600 and 800 °C and characterized by using XRD and TGDTA. From XRD it confirms that CoFe₂O₄ nano particles belongs to spinel type lattice of space group Fd3m. The CoFe₂O₄ nano particles calcinated at 600 °C were further characterized by using FE-SEM with EDAX, FE-TEM with SAED pattern, DLS zeta potential and CV. The linear relationship between particle size and calcination temperatures of CoFe₂O₄ nanoparticles was noticed. The surface morphology of CoFe₂O₄ studied through FE-SEM and FE-TEM indicate that the particles are found crystalline and are in cubic shape. EDAX analysis revealed the presence of Co, Fe and O. Zeta potential exposes the good stability of the prepared CoFe₂O₄ nanoparticles. Capacitance value 609 F g^?1 was observed for the scanning rate of 2 mV s^?1 from the CV study and concluded it is suitable for super capacitor application.