The Relevance of Powder/Liquid Wettability to the Cohesiveness of Carbon Black Agglomerates

Particle size enlargement operations often involve the use of a liquid to improve powder cohesiveness. Capillary suction and surface tension forces acting through liquid menisci between particles are the primary source of the cohesive bonding. The strength of these forces, and consequently the strength of the wet agglomerate, is dependent upon the total liquid content, its distribution within the agglomerate, and the powder wettability (characterized by the liquid surface tension and powder/liquid contact angle). The tensile strength of powder compacts containing submicron carbon black particles has been measured as a function of saturation level for several liquids. It is found that the compact strength increases with increasing surface tension for liquids that exhibit a zero contact angle. Above the critical surface tension for wetting a more complicated situation exists where both the surface tension and contact angle are important.     

Effects of Plasma Etching on Surface Modification and Gas Permeability of Bisphenol‐A Polycarbonate Films

The surface fluorination of polycarbonate bisphenol‐A thin films was carried out by treatment with plasma of sulfur hexafluoride/argon (SF₆/Ar) using a radio frequency (RF) discharges. Effects of treatment time and SF₆ concentration have been studied. Surface characterization was performed using X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy with attenuated total reflectance (FT‐IR/ATR), atomic force microscopy (AFM) and contact angle measurements. The effects of the surface modification on the carbon dioxide (CO₂) gas permeation of the fluorinated films were evaluated. The results showed effective fluorination of all samples, with C‐F, C‐F₂ and even C‐F₃ groups attached to the polycarbonate, depending on the treatment conditions. The presence of incorporated fluorine molecules absorbed into the polymer structure during treatment was also shown. The polymer films showed an increase of their surface roughness and a decrease in their surface tension due to the plasma treatment. Plasma fluorination also decreases polycarbonate CO₂ permeability considerably. The films treated with the lower concentration of SF₆ showed the highest barrier values; however, significant differences between the permeability values for the samples treated for different times were not observed.     

The Roton Minimum: Is it a General Feature of Strongly Correlated Liquids?

The roton minimum is a deep minimum in the collective excitation spectrum of the liquid, forming around fairly high k ‐values. We have discovered, through MD simulations, that this appears to be a general feature of strongly coupled liquids and is ubiquitous in 2D and 3D Yukawa liquids. We suggest that the physical origin of the roton minimum has to be sought in the quasi‐localization of particles in a strongly correlated liquid and in the ensuing formation of local microcrystals whose averaged frequency dispersion would show roton minimum‐like feature (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and propanol mixtures

Measurements of advancing contact angles (θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and propanol mixtures at constant TX-100 concentration equal to 1 × 10⁻⁷, 1 × 10⁻⁶, 1 × 10⁻⁵, 1 × 10⁻⁴, 6 × 10⁻⁴ and 1 × 10⁻³ M, respectively, on polytetrafluoroethylene (PTFE) and polymethyhmethacrylate (PMMA). Using obtained results the changes of cosθ and adhesional tension against surface tension of all series of aqueous solutions of TX-100 and propanol mixtures (γ_LV) for PTFE and PMMA surfaces were shown. On the basis of these changes it was deduced that adsorption of TX-100 and propanol mixtures at PTFE-solution and solution-air interfaces is the same but the adsorption of TX-100 and propanol mixtures at solution-air interface is considerably higher than at PMMA-solution one. In the case of PTFE this conclusion was confirmed by relationship between cosθ and the reciprocal of the surface tension of solution. Extrapolation of the relationships between cosθ and/or adhesional tension and the surface tension of solutions to the points corresponding to the cosθ = 1 and adhsional tension equal to the surface tension of solution, the critical surface tension of PTFE and PMMA wetting was determined. The average values of critical surface tension of wetting determined from these relationships for PTFE are lying in the range of its surface tension values determined from contact angles of different kinds of liquids, which can be find in the literature, but for PMMA are considerably lower than the surface tension. The double value of the critical surface tension of PTFE wetting is equal to adhesion work of the solution to its surface and for PMMA there is not any correlation between these magnitudes.Using the measured values of the contact angles and Young equation the PTFE(PMMA)-aqueous solution interfacial tension was determined. The interfacial tension values of PTFE-aqueous solution were also calculated from the Fainerman and Miller equation in which the correcting parameter of nonideality of the surface monolayer was introduced and compared to those obtained from Young equation. From this comparison it results that the changes of PTFE-solution interface tension as a function of propanol concentration can be described by the Fainerman and Miller equation.     

The interfacial energy of two-dimensional bidisperse cellular fluids

The mixing energy of two biphasic fluid systems (dispersions of two liquids or a liquid and a gas, A and B in a liquid C), confined between two parallel plates, is calculated. Our attention is limited to concentrated and monodisperse systems, i.e. emulsions and foam/emulsions consisting of equal-size (if of the same composition) cells separated by a thin liquid film. It is demonstrated that the multiphase mixtures ordered into regular patterns can be stable in a wide range of interfacial tensions acting along A-C and B-C interfaces and also in a wide range of volume fractions of fluid A. Anisotropic properties of such well-ordered structures are also demonstrated.Received: 8 December 2003, Published online: 4 May 2004PACS: 83.80.Iz Emulsions and foams - 05.65. + b Self-organized systems     

亚微米聚苯乙烯微球在气-液界面组装的机理研究

系统地研究了亚微米聚苯乙烯微球在气-液界面的组装机理.聚苯乙烯微球在介质对流的带动下会到达悬浮液的表面并在气-液界面组装，气-液界面处聚苯乙烯微球间由弯液面产生的毛细管力是组装的推动力.界面处聚苯乙烯微球在干燥过程中其润湿性发生了转变，由完全润湿到部分润湿并最终变成不润湿，相应的聚苯乙烯微球与分散介质间接触角也逐渐增大.研究表明，只有接触角达到或超过某数值θ′_critical时，才能够出现气-液界面组装现象.考虑到PS胶粒晶体的表面是“规则”粗糙的表面，由Wenzel公式知θ′_critical大于测量值θ＝22°.聚苯乙烯微球润湿性的转变是界面组装发生和持续进行的关键性因素. 关键词： 自组装 胶粒晶体 聚苯乙烯微球 润湿性     

亚微米聚苯乙烯微球在气-液界面组装的机理研究

系统地研究了亚微米聚苯乙烯微球在气-液界面的组装机理.聚苯乙烯微球在介质对流的带动下会到达悬浮液的表面并在气-液界面组装，气-液界面处聚苯乙烯微球间由弯液面产生的毛细管力是组装的推动力.界面处聚苯乙烯微球在干燥过程中其润湿性发生了转变，由完全润湿到部分润湿并最终变成不润湿，相应的聚苯乙烯微球与分散介质间接触角也逐渐增大.研究表明，只有接触角达到或超过某数值θ′_critical时，才能够出现气-液界面组装现象.考虑到PS胶粒晶体的表面是“规则”粗糙的表面，由Wenzel公式知θ′_critical大于测量值θ＝22°.聚苯乙烯微球润湿性的转变是界面组装发生和持续进行的关键性因素. 关键词： 自组装 胶粒晶体 聚苯乙烯微球 润湿性     

Isochoric temperature coefficient of surface tension andS o-parameter of quasi-spherical molecular liquids

The Sharma parameterS _o which is characteristic of molten alkali halides and polymers has also been shown to be characteristic of a wide variety of liquids. Calculated data using the volume expansivity of the liquid establish the constancy of theS _o-parameter which retains, on an average, a constant value of 1·11 for quasi-spherical molecular liquids. It is shown thatS _o-parameter is also related to volume expansivity of the surface layer of the liquid, temperature coefficient of surface tension of liquids and describes the temperature and volume or pressure dependence of thermodynamic Grüneisen parameter and isochoric heat capacity with significant contribution for influencing the thermoacoustic and surface tension properties of liquids.     

Fluorinated nanocarbons using fluorinating agent: Strategies of fluorination and applications

The fluorination method strongly influences the physical properties of the resulting fluorinated carbon materials. Two fluorination ways, direct fluorination under pure fluorine gas and controlled fluorination by the decomposition of TbF₄, have been used for the fluorination of particular nanocarbons: carbon nanofibers and a mixture of carbon nanodiscs and nanocones. Then, fluorocarbon matrix structures have been determined owing to solid state ¹⁹F NMR for MAS conditions at a spinning speed of 30 kHz. It reveals that the fluorination mechanism depends on the fluorination conditions but not on the starting nanocarbons morphology, i.e. tubular or planar. Finally, the electrochemical properties of carbon nanofibers fluorinated by the two ways are detailed. Controlled fluorination allows an increase of the power densities of fluorinated carbon nanofibers used as electrode in primary lithium batteries.     

Computational study on cell structure evolution of random liquid and metal-melt foams

A method for geometrical and topological modeling the evolution of close-cell metallic foams based on the Voronoi tessellation in three-dimensional space is presented. Numerical computations were carried out to examine the evolution of the bubble size distribution and topological and geometric properties of aluminum foams in the liquid state, which were implemented by using McPherson’s new theory on coarsening of microstructures as well as the topological transition rules (T1 and T2 processes) in 3D foams, accounting for remarkable effects of both the gas diffusion and surface tension. Computational results show that the bubble size distributions of metallic foams are strongly coupled to the evolution of the cellular structure and dependent on the gas diffusivity and surface tension. The way of foam coarsening can be expressed as RR ₃₂=−mt ²+1 approximately, and gas diffusion between bubbles dominates the evolution of bubble sizes and foam structures. It is found that the average number of faces per bubble is 〈f〉=13.8, which is in good agreement with the values reported in the literature.     

Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions

The metastable liquid phase separation and rapid solidification behaviours of Co_61.8Cu_38.2 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing, electromagnetic levitation (EML) and drop tube techniques. It is found that the liquid phase separation process and the solidification microstructures intensively depend on the experimental processing parameters, such as undercooling level, cooling rate, gravity level, liquid surface tension and the wetting state of crucible. Large undercooling and surface tension difference of the two liquids tend to facilitate further separation and cause severe macrosegregation. On the other hand, rapid cooling and low gravity effectively suppress the coalescence of the minority phase. Severe macrosegregation patterns are formed in the bulk samples processed by both DTA and EML. In contrast, disperse structures with fine spherical Cu-rich spheres homogeneously distributed in the matrix of Co-rich phase have been obtained in drop tube.     

氟化时间对环氧树脂绝缘表面电荷积累的影响

为抑制环氧树脂绝缘的表面电荷积累、研究处理时间对表面电荷积累的影响, 使用氟/氮混合气在实验室反应釜中对环氧试样进行了不同时间(10 min, 30 min和60 min)的表面氟化处理. 衰减全反射红外分析与SEM断面和表面观察表明随氟化时间的增加, 氟化层的氟化度和厚度增大, 表面微观粗糙度降低、表面组织变得致密. 与开路热刺激放电电流测量所表明的、未氟化(原)试样有深的表面电荷陷阱和稳定的表面电荷相比, 这些氟化试样的表面不能存储电荷. 沉积在它们表面上的电晕电荷于室温下分别约在2 min, 10 min和15 min内快速衰减为零, 展现随氟化时间的延长而减慢的电荷释放速率. 表面电导率和接触角测量及表面能计算表明氟化引起表面电导率和表面润湿性与极性的显著增加, 但它们随氟化时间的延长而减小. 氟化试样表面电导率的显著增大归因于表面电荷陷阱的非常可能的实质变浅和表面吸附的水分. 表面充电电流测量进一步地表明, 与原试样几乎为零的稳态表面电流相比, 这些氟化试样在连续充电期间显现大的稳态表面电流. 这意味着这些氟化试样在充电期间比原试样有少得多的表面电荷积累.     

Influence of fluorination and chain length on the static dielectric properties of nematogenic bi-cyclohexyl phenyl derivatives

Effects of fluorination and chain length of six bi-cyclohexyl phenyl compounds (3ccp-f, 3ccp-ff, 3ccp-fff, 5ccp-f, 5ccp-ff, 5ccp-fff) on their physical properties have been investigated. All the compounds exhibit nematic phase over a wide range of temperatures. Molecular mechanics calculation reveals that dipole moments of the molecules increases (1.93D to 3.37D) with fluorination in both propyl- and pentyl-based systems; increment in f to ff derivatives is more than in ff to fff derivatives. However, no change in dipole moment is observed with increased chain length. In the nematic phase, average value of dielectric constant (?_avg) is less than the extrapolated values of ?_iso in isotropic phase. Increased fluorination also decreases splay elastic constant, and thus faster response is expected in triply fluorinated compounds.     

Primary isotopic effect on the magnetic shielding of tin nuclei (117Sn and 119Sn)

The Kirkwood-Buff statistical mechanical theory of surface tension γ for monatomic fluids is extended to molecular fluids. A rigorous expression for γ is derived in terms of the angular pair distribution function f(z ₁ R ₁₂θ₁θ₂) of an equilibrium fluid-fluid system (liquid-gas, liquid-liquid, or gas-gas). The Fowler approximation is applied for the liquid-gas case, and a simple expression for γ is derived in terms of the bulk liquid angular pair correlation function g(R ₁₂θ₁θ₂). Thermodynamic perturbation theory for g(R ₁₂θ₁θ₂) is also used to calculate γ theoretically. The theoretical results are compared with experimental values.     

Laser-assisted shape selective fragmentation of nanoparticles

Experimental results are presented on laser-assisted fragmentation of gold-containing nanoparticles suspended in liquids (either ethanol or water). Two kinds of nanoparticles are considered: (i) elongated Au nanorods synthesized by laser ablation of a gold target immersed in liquid phase; (ii) gold-covered NiCo nanorods with high aspect ratio (θ ∼ 10) synthesized by wet chemistry processes. The shape selectivity induced by laser fragmentation of these nanorods is gained via tuning the wavelength of laser radiation into different parts of the spectrum of their plasmon resonance corresponding to different aspect ratios θ. Fragmentation is performed using three laser wavelengths, involving a Cu vapour laser (510 and 578 nm) and a Nd:YAG (1064 nm). Nanoparticles are characterized by UV-vis spectrometry, Transmission Electron Microscopy (TEM). The effect of laser pulse duration (nanosecond against picosecond range) is also studied in the case of fragmentation with an IR laser radiation.     

Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface‐enhanced Raman scattering spectroscopy

Two kinds of room‐temperature ionic liquids, 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) and 1‐butyl‐3‐methylimidazolium tetrafluoroboride ([BMIM]BF₄), were used as solvent, and the adsorption of the ionic liquids themselves and of N‐methylimidazole (NMIM) were investigated by electrochemical surface‐enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the [BMIM]BF₄ liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br⁻, the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM)₄Br]Br·H₂O and [Cu(NMIM)₄](BF₄)₂ were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of the Breakage and Wetting Parameters of Calcite and Their Correlations

This paper presents the breakage and wetting parameters of calcite mineral obtained experimentally and establishes a correlation between these characteristic parameters. The breakage parameter obtained from the different feed sizes of grinding is the specific rate of breakage (S_i). The wettability parameter, obtained from surface chemistry‐based processes such as contact angle measurements or flotation methods, is the critical surface tension of wetting of a solid or mineral (γ_c). Calcite mineral, studied for the determination of the above parameters and their correlations, was ground in a laboratory‐size ceramic ball mill with dry, wet and chemically aided grindings and tested extensively to determine the γ_c values by using a contact angle goniometer and a newly designed micro‐column flotation cell. The highest S_i value obtained was 0.35 min^?1 for sodium dodecyl sulfate (SDDS)‐aided grinding, and the lowest S_i value was 0.26 min^?1 for dry grinding of the ?600+425 feed in the mill. The γ_c values for calcite were obtained as 34.0–34.9 mN/m for SDDS‐treated calcite surfaces, 29.9–31.4 mN/m for sodium oleate‐treated surfaces and >72 mN/m for both dry and wet ground products whose surfaces were not treated chemically. Some correlations were established between the S_i and γ_c parameters; as the S_i increases, γ_c decreases, indicating that relatively more hydrophobic surfaces are broken faster for the largest sizes, resulting in higher S_i values with more fines (lower γ of B_{i, j}) in the finer size distribution region (i.e. ?150 μm).     

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and short chain alcohol mixtures

Measurements of advancing contact angles (θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and methanol and ethanol mixtures at constant TX-100 concentration equal to 1 × 10⁻⁷, 1 × 10⁻⁶, 1 × 10⁻⁵, 1 × 10⁻⁴, 6 × 10⁻⁴ and 1 × 10⁻³ M, respectively, on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA). Using measured contact angle values the relationships between cos θ, adhesion tension and surface tension of the solutions were determined, and on their basis the critical surface tension of PTFE and PMMA wetting was calculated. The obtained average value of the critical surface tension of PTFE wetting is lying in the range of the PTFE surface tension values which can be found in the literature, while for PMMA it is even lower than the Lifshitz-van der Waals component of its surface tension. From the relationship between the adhesion and surface tension and Lucassen-Reynders equation it results that in the case of PTFE the adsorption at the PTFE-solution and solution-air interfaces is the same, which was confirmed by a linear relationship between the cos θ and 1/γ_LV and intercept on cos θ axis equal to −1. However, for PMMA the adsorption of the surface active agents at solution-air interface is higher than at PMMA-solution. Using the values of the contact angle the values of the adhesion work of solution to the PTFE and PMMA surface were also determined, which are constant for PTFE, but for PMMA decrease with alcohol concentration increase. Next, using the contact angle values in the Young equation, the PTFE(PMMA)-solution interface tension was also calculated. The obtained values of PTFE-solution interface tension were compared with those evaluated from the Szyszkowski, Connors and Fainerman and Miller equations, and good agreement between these values was observed for all series of TX-100 and alcohol mixtures at a low alcohol concentration.     

Designing Zwitterionic SiO2NH2‐Au Particles with Tunable Patchiness using Wrinkles

A facile template‐based approach toward zwitterionic SiO₂NH₂‐Au patchy particles is presented. Therefore, wrinkle templates prepared by stress release in a bilayer system comprised of an elastic PDMS fundament and a thin SiO_x top layer are used. After aligning positively charged, amine‐functionalized silica particles in wrinkle grooves, their surfaces are partially modified with negatively charged gold nanoparticles in an electrostatic adsorption step. Patchiness is precisely controlled by the degree of immersion of the initial particles into wrinkles of varying dimensions. By ultrasonication or wetting with a water droplet, patchy particles are easily released from the substrate‐yielding particles with two oppositely charged hemispheres. Interfacial tension measurements prove the surface activity of the SiO₂NH₂‐Au particles in an oil/water system and are explained in the view of the Janus‐type surface charges of the particles and the charge of the oil/water interface.     

Accumulation of particles in time-dependent thermocapillary flow in a liquid bridge. Modeling of experiments

The study addresses the phenomenon of accumulation of rigid tracer particles suspended in a time-dependent thermocapillary flow in a liquid bridge. We report the results of the three-dimensional numerical modeling of recent experiments [1,2] in a non-isothermal liquid column. Exact physical properties of both liquids and particles are used for the modeling. Two liquids are investigated: sodium nitrate (NaNO₃) and n-decane (C₁₀H₂₂). The particles are modeled as perfect spheres suspended in already well developed time-dependent thermocapillary flow. The particle dynamics is described by the Maxey-Riley equation. The results of our simulations are in excellent agreement with the experimental observations. For the first time we reproduced numerically formation of the particle accumulation structure (PAS) both under gravity and under weightlessness conditions. Our analysis confirms the experimental observations that the existence of PAS depends on the strength of the flow field, on the ratio between liquid and particle density, and on the particle size.