Vapor dispersion near a surface of evaporation

Theoretical and experimental data are presented which indicate the need to consider two mechanisms of vapor dispersion in actual processes for preparation of vacuum condensates.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 1, pp. 40–43, January, 1976.     

Removal of organic impurities from sewage by evaporation through polymer membranes

Pervaporational nonporous membranes are obtained on the basis of synthetic rubber. The possibility of using the method of evaporation through the obtained membrane is considered for treatment of sewage resulting from styrene, polysterene, polycarbonate, and polysulfone production. “Kiev Polytechnic Institute” National Technical University of Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 6, pp. 986–988, November–December, 1996.     

无定型PEO聚合物的合成及导电性能研究

利用低分子量PEG(Mn=400)合成了高分子量的聚氧化乙烯(PEO)嵌段聚合物。采用电化学方法——电渗析除尽了经常规方法(吸附、过滤、沉淀等)所不能除尽的微量杂质,得到纯化产物。通过GPC测得其平均分子量可达105。XRD和1HNMR表明其结构是以[CH2O(CH2CH2O)n]为重复单元的无定型聚合物,其与LiClO4络合物通过10％SiO2纳米材料补强后的固态电解质成膜性和导电性均良好。在测量温度范围内,电导率随温度的变化遵循Arrhenius关系式,22℃时Li+电导率达3.27×10-5 S/cm。     

水铝英石/PEO/LiClO4复合固态聚合物电解质中组分相互作用对PEO结晶的影响

为解决现有锂离子电池的安全性问题,固态电解质的研究备受关注。以Na2SiO3和AlCl3·6H2O为原料,采用溶胶-凝胶法制备出水铝英石(AL);通过溶液共混法将其与聚环氧乙烷/高氯酸锂(PEO/LiClO4)复合得到复合固态聚合物电解质。利用X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、差示扫描量热分析仪(DSC)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)以及光学显微镜(OM)对样品进行结构分析及形貌表征。结果表明:水铝英石和LiClO4与PEO间的非价键力相互作用(络合、氢键及Lewis酸-碱作用)显著抑制PEO的结晶。随着水铝英石含量的增加,PEO的结晶度呈现出先降低后增加的趋势;而随着锂盐含量的增加,PEO的结晶度持续降低,当EO/Li+摩尔比为10∶1,水铝英石的含量为5%(质量分数)时,复合固态聚合物电解质的结晶度最低,仅为4.12%。     

Sound dispersion in a relaxing polymer fluid with bubbles

Results are presented of an investigation of the singularities of sound wave propagation in a polymer solution with bubbles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 1, pp. 63–69, January, 1985.     

Problem of hydroxyapatite dispersion in polymer matrices: a review

This review summarizes recent work on manufacturing biocomposites suitable for bone tissue engineering. There is a great need to engineer multi-phase (i.e. composite) materials that combine the advantages exhibited by each component of the material, with a structure and composition similar to that of natural bone. The discussion concentrates on the preparation of nanocomposites containing hydroxyapatite particles (one of the most widely used bioceramics materials) with polymer matrices. Special attention is paid to the preparation of nanocomposites with individual (non-aggregated) nanoparticles because this is a key problem in nanotechnology industrialization. Controlling the mixing between so two dissimilar phases is a critical challenge in the design of these inorganic-organic systems. Several approaches that may be applied to overcome this problem will be described in this review.     

Powder dispersion and aqueous tape casting of YSZ-NiO composite

Powders of YSZ and NiO were prepared by precipitation of hydroxides, calcination and wet grinding. The dispersion conditions were optimized from zeta-potential and viscosity studies. Aqueous suspensions of both the powders exhibited maximum zeta-potential values in two ranges of pH, 3 to 4 (positive) and 9 to 11 (negative), establishing the feasibility of a dispersion of both oxides together. Viscosity measurements indicated presence of effective dispersion of a 1:1.5 mixture of YSZ:NiO below a solid concentration of 25 volume percent. Aqueous tape cast slurries were formulated using PVA solution as binder and glycerol as plasticizer. The rheological behavior of these slurries (viscosity and visco-elastic parameters) was strongly influenced by slight variation in the solid content. Visco-elastic measurements revealed all the slurries to be predominantly viscous and become more elastic with increasing solid content. Defect free flat tapes could be obtained by casting the slurry with optimum flow characteristics (i.e., pseudoplastic but non-thixotropic) that could be sintered to flat sheets with 80% T.D. (theoretical density) and 20% O.P. (open porosity) at 1450°C. Upon reduction in hydrogen at 1000°C, it formed in to YSZ-Ni composite that retained the same micro structural features of YSZ-NiO.     

Synthesis of acicular iron oxide nanoparticles and their dispersion in a polymer matrix

An alternative forced hydrolysis approach for the synthesis of -FeOOH of varying dimensions was achieved. The -FeOOH particles were converted into -Fe₂O₃ in a colloidal process, which eliminated the agglomeration of -Fe₂O₃ particles. The acicular -Fe₂O₃ nanoparticles could be readily dispersed into an organic solvent. Preliminary studies have demonstrated that the dispersion of the -Fe₂O₃ nanorods in a polymer matrix is feasible leading to an organic-inorganic nanocomposite.     

PEO基固态聚合物电解质膜的静电纺丝制备及性能EI北大核心CSCD

PEO基固态聚合物电解质被认为是目前固态锂电池领域极具产业化前景的固态电解质。为适应工业化生产,采用静电纺丝技术制备PEO/LiClO_(4)固态聚合物电解质(SPE),研究纺丝电压、纺丝液质量浓度和锂盐含量对SPE纤维膜形貌和直径的影响。通过扫描电子显微镜观察SPE中纤维的形貌,利用Image J软件分析SPE纤维的直径。通过DSC,XRD,FTIR-ATR和拉伸测试等手段对静电纺丝制备的SPE纤维膜的组成、结构、性能等进行研究。结果表明:当纺丝电压为15 kV、PEO/LiClO_(4)纺丝液质量浓度为6%、[EO]∶[Li^(+)]=10∶1(摩尔比)时,静电纺丝方法制备的PEO/LiClO_(4) SPE纤维膜具有较好的纤维形貌,平均直径为557 nm,分布均一;当[EO]∶[Li^(+)]=10∶1时,SPE纤维膜中PEO的熔点仅为53.8℃,结晶度低至18.9%;电解质在30℃时的离子电导率达到5.16×10^(-5)S·cm^(-1),同时具备良好的电化学稳定性和界面稳定性。     

Novel approach for the selective dispersion of MWCNTs in the Nylon/SAN blend system

Multiwalled carbon nanotubes (MWCNTs) were coated with TiO₂ by sol gel process. The coating was confirmed by TEM, XPS and XRD. TEM analysis showed that rough coating was formed on the MWCNTs. These modified MWCNTs and pristine MWCNTs were dispersed in the blend of nylon 66 and SAN by melt blending. FESEM images showed that pristine MWCNTs were preferably dispersed in the nylon phase whereas TiO₂ modified MWCNTs confined to the SAN phase. The selective dispersion was explained on the basis of migration and stabilization of these high aspect ratio nanotubes in the Nylon/SAN blend system. The hydrogen bonding interaction between the CN group of SAN and surface hydroxyl group of TiO₂ coated MWCNTs has restricted the migration of modified MWCNTs from SAN to nylon phase.     

Effect of dispersion of MWCNTs on the static and dynamic mechanical behavior of epoxy matrix nanocomposites

In this investigation, specimens of MWCNT-epoxy nanocomposites were prepared by two different dispersion methods including the use of ultrasonication, and high speed shear mixing. The dispersion degree between MWCNT and polymer resin was analyzed after completing the curing reaction, by scanning electron microscopy. The effect of the nanotubes dispersion achieved on the properties of the manufactured nanocomposite was analyzed through static three point bending tests and dynamic mechanical thermal analysis. Interesting results concerning the dispersion effect of MWCNTs added to the polymer matrix on the storage and loss moduli as well as on tanδ and T _g values of the specimens manufactured by the sonication and high speed shear mixing methods were derived.     

Large-scale fabrication of ZnO nanocrystals by a simple two-step evaporation–oxidation approach

Single crystal structures of ZnO nanocrystals were prepared on quartz and polyimide (PI) film substrates by using a thermal coater to promote thermal evaporation, followed by air circulation at 350 °C for 2 h to effect oxidation. HRTEM and TEM images show the individual ZnO nanocrystals have regular lattice order without stacking faults. After dispersion by an ultrasonic bath, ZnO deposited on PI film substrates can consist of individual and well-distributed nanocrystals with an average crystal size of 20–30 nm. In photoluminescence, the nanocrystalline ZnO exhibits strong UV emission at 395 nm, with no emission in the visible spectrum. The synthetic method described in this paper provides a simple and efficient method to fabricate ZnO nanocrystals on a large scale.     

Preparation and study of conductivity in lithium salt complexes of mixed MEEP : PEO polymer electrolytes

Poly(ethylene oxide)-LiX complexes and poly[bis(methoxy ethoxy ethoxide) phosphazene]-LiX complexes of polymer thin films were prepared. Conductivity measurements were carried out and the values were found to lie between 10⁻⁸ and 1.7 × 10⁻⁵ (S/cm). MEEP : LiX salts showed higher conductivity than PEO-LiX salts despite lower dimensional stability. For enhancing stability and conductivity, MEEP-PEO : (LiX) _n systems were prepared and conductivity measurements carried out. Further the MEEP/PEO : (LiX) _n was doped with Al₂O₃ and TiO₂ nanocomposite ceramic fillers and the conductivity was studied. The conductivity vs temperature plots showed the enhancement of conductivity with TiO₂ added nanocomposite ceramic fillers. The enhanced conductivity is explained on the basis of the effect of local structural modification—promoting localized amorphous region—for enhancement of the Li⁺ ion transport.     

Pore-scale dispersion in electrokinetic flow through a random sphere packing

The three-dimensional velocity field and corresponding hydrodynamic dispersion in electrokinetic flow through a random bulk packing of impermeable, nonconducting spheres are studied by quantitative numerical analysis. First, a fixed bed with interparticle porosity of 0.38 is generated using a parallel collective-rearrangement algorithm. Then, the interparticle velocity field is calculated using the lattice-Boltzmann (LB) method, and a random-walk particle-tracking method is finally employed to model advection-diffusion of an inert tracer in the LB velocity field. We demonstrate that the pore-scale velocity profile for electroosmotic flow (EOF) is nonuniform even under most ideal conditions, including a negligible thickness of the electrical double layer compared to the mean pore size, a uniform distribution of the electrokinetic potential at the solid-liquid interface, and the absence of applied pressure gradients. This EOF dynamics is caused by a nonuniform distribution of the local electrical field strength in the sphere packing and engenders significant hydrodynamic dispersion compared to pluglike EOF through a single straight channel. Both transient and asymptotic dispersion behaviors are analyzed for EOF in the context of packing microstructure and are compared to pressure-driven flow in dependence of the average velocity through the bed. A better hydrodynamic performance of EOF originates in a still much smaller amplitude of velocity fluctuations on a mesoscopic scale (covering several particle diameters), as well as on the microscopic scale of an individual pore.     

Correlation between dispersion state and electrical conductivity of MWCNTs/PP composites prepared by melt blending

Non-conductive polymers filled with conductive carbon nanotubes (CNTs) often do not show detectable conductivity due to poor dispersion of carbon nanotubes in the polymer matrix and the lack of conductive networks formed from CNTs. In this work, we attempted two ways to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in a polypropylene (PP) matrix: chemical modification of MWCNTs and addition of a master batch as a compatibilizer, followed by melt blending using a micro-compounder. The relationship between the dispersion state of MWCNTs and the electrical conductivity of the CNTs/PP composites have been investigated by controlling several factors such as CNTs modification, compatibilization by a master batch, melt mixing, and post-heat treatment. The enhanced interfacial adhesion between the CNTs and the polymer could improve the dispersion of CNTs but it could also reduce the electrical conductivity of the composites. Meanwhile, it is interestingly found that the post-heat treatment could increase the conductivity remarkably due to the connection of CNTs into networks. Thus, it is concluded that the balance between dispersion of CNTs and the formation of conductive networks plays an important role in enhancing the electrical conductivity of composites.     

pH controlled dispersion and slip casting of Si3N4 in aqueous media

The dispersion characteristics of commercial Si₃N₄ powder in aqueous media (deionized water) was studied as a function of pH in the range 2–11. The slip was characterized for its dispersion quality by various experimental techniques like particle size analysis, sedimentation phenomena, viscosity and flow behaviour and zeta potential analysis. The optimum dispersion was found to be in the pH region 9–11 wherein the slurry displayed minimum sedimentation height, minimum viscosity, near Newtonian flow behaviour and maximum zeta potential. The slip is highly agglomerated in the pH range 2–8 as manifested by higher sedimentation height, higher viscosity, lower zeta potential and thixotropic non-Newtonian flow behaviour. The 72 wt% (44 vol.%) Si₃N₄ slips made at pH = 10 resulted in green bodies having 53–59% of theoretical density after casting into plaster molds.     

Buoyancy effect on dispersion of a solute in a flow through a horizontal channel

Summary The paper is concerned with the statistical study of the dispersion of a cloud of solute injected into a combined free and forced convective laminar flow through a parallel plate channel under the action of a uniform linear axial temperature variation along the channel walls, including the buoyancy forces. The main idea is to study the effect of the Grashof number on the variance, skewness, and kurtosis of the distribution of concentration of the solute for all time. It is found that there is a critical Grashof number for which the distribution of concentration about the mean is exactly a Gaussian function.With 6 Figures     

Pattern formation through reaction and diffusion in a simple pooled-chemical system

The formation of spatial patterns is considered for a reaction-diffusion system based upon the cubic autocatalator, A+2B→3B, B→C, with the reaction taking place inside a closed vessel, the reactant A being replenished by the slow decay of a precursor P via the simple step P→A.

Patterns are shown to form only when the dimensionless diffusion coefficient λ is sufficiently small, with the number of available patterns increasing as λ diminishes to zero. Two types of patterns occur, standing-wave patterns arising out of Hopf bifurcations, together with steady-wave patterns arising out of pitchfork bifurcations. The local behaviour on the bifurcating branches is obtained via weakly nonlinear theory. Close to its point of bifurcation, each pattern is shown to be partially stable; that is, it remains stable to small disturbances composed of its own, or any higher spacial wave numbers. However, the pattern is unstable to disturbances with smaller spatial wave number than its own. This partial stability is in line with observations of pattern formation in chemical systems for which the cubic autocatalator provides a rational model. Such patterns are not generally observed to have absolute local stability, but appear and disappear in a transient manner, influenced by the external disturbances to the system. Moreover, patterns do not appear after the system has been well stirred. This is also in line with the present theory, which demonstrates that a spatially uniform state is always the most stable. For a typical case, the bifurcation branches are extended by numerical integration, which reveals a connecting of two branches through a further symmetry-breaking bifurcation.