Droplet impingement and wetting behavior on a chemically heterogeneous surface in the Beyond–Cassie–Baxter regime

Droplet impingement and anisotropic wetting on chemically heterogeneous stripe-patterned surfaces is simulated by means of many-body dissipative particle dynamics. The ratio of the stripe width and initial droplet diameter, defined as β, ranges from 0.5 to 1.0 so that the wetting process is in the Beyond–Cassie–Baxter regime and is highly anisotropic. At zero Weber number (that is, without considering droplet inertia) and with superhydrophobic stripes, β is the only factor affecting the droplet perpendicular contact angle and aspect ratio. For inertial droplets, β and the Weber number are found to have an effect on the eventual droplet morphology on multi-striped surfaces. These morphologies include elongated shape, split-off, and “butterfly” shape. A correlation for critical split-off conditions has been determined. An energy analysis of droplet impingement shows that the normalized surface energy of the droplet is independent of the Weber number if the droplet is elongated or butterfly-shaped.     

Microstructure evolution upon annealing of a ZrB2–SiC composite containing lanthana and magnesia

The purpose of this work was to produce a dense ZrB₂–SiC ceramic and to identify a suitable annealing cycle to crystallize the glassy phase and promote SiC growth along the c axis. The concept behind this work exploits the irreversible SiC β → α transformation occurring at temperature above 1900 °C, in such a way to have SiC platelets able to trigger effective toughening mechanisms. La₂O₃ and MgO were used as sintering additives. The as sintered and annealed materials were examined through X-ray diffraction (XRD), to identify the crystalline phases, scanning electron microscope (SEM), to study the distribution of the secondary phases, and transmission electron microscope (TEM), to analyze the microstructure at nanoscale level, with particular attention to new crystalline phases and to the interfaces in high resolution mode. A model for the microstructure evolution during densification and upon annealing is presented.     

How does the shape and surface energy of pores affect the adsorption of nanoconfined fluids?

We report a systematic molecular simulation study of the behavior of Lennard–Jones fluids inside nanopores of diverse shapes, focusing on the effect that the pore geometry and the local energetic environment have on the adsorption isotherms. Infinitely long pores with polygon (triangle, square, pentagon, hexagon, octagon, decagon, and circle) cross sections are considered. Three different pore sizes commensurate with the molecular diameters along with three different values of fluid–solid energy interactions are chosen to perform Grand Canonical Monte Carlo simulations at a subcritical temperature. Overall, the effect of nanoconfinement on the adsorption of fluids is seen to be a delicate balance between the geometric packing restrictions imposed by the hard cores of the molecules and the surfaces, the excess adsorption induced by the presence (or absence) of energetically favored “hot spots” and the overall ratio of surface/bulk fluid volume present in the pore.     

Failure of a Steel Spherical Particle upon Impact on High‐Porous Sheets

The failure of a 2mmdiameter steel particle upon normal impact with a velocity of 1.5–7.3 km/sec onsheets 1 mm thick was studied. Two types of sheets were used: continuous sheets of Duralumin and highporous sheets of a copper powder. The depth of the largest crater and the positions, areas, and effective diameters of all craters were measured on the witness plate. Values of the threshold impact velocities for the beginning of failure of the steel particle and distributions of the number of craters in size and radius from the impact point were obtained for various impact velocities. It is shown that at identical impact pressures near the failure threshold, the lowdensity highporous sheets break up the steel particle better than the Duralumin sheets. This is possibly caused by the thermal explosion of the sheet material in the collision region, which increases the time of interaction of the impactor with the sheet.     

Fabrication of two sites hydrophobicity on cotton surface – a fluoropolymerization approach

Cotton fabric on both surfaces was coated with polymerization of fluoromonomer followed by adsorption of fluorosurfactant by a new technique admicellar polymerization to obtain durable hydrophobicity. Water repellence properties were determined in terms of simple drop test contact angles. The coating on cotton fabric exhibited the right water contact angle of 137.23° and left contact angle 138.35° (an average value of 137.79°). However, the durability of the coatings was decreased after simple home laundering with a decrease in water contact angle value. The surface morphology was evaluated by scanning electron microscopy before and after polymerization. Beside this chemical composition on the cotton, the surface was evaluated by EDS analysis to determine the number of fluorine moieties deposited on the cotton surface by this technique.     

Formation of abnormally large-sized tubular amyloid �� aggregates on a nanostructured gold surface

The effect of the properties of a nanostructured gold surface (nano-Au surface) on the aggregation of Amyloid ??(1?C40) (A??40) was investigated. A nano-Au surface, in the form of immobilized nanoparticles, was prepared by using a thermal evaporator, resulting in the formation of nanosized clusters with sizes less than 10 nm. When A??40 was incubated with the nano-Au surface, abnormally large-sized tubular aggregates were formed on the surface and typical fibril formation was suppressed in the solution. This abnormally large tubular structure represents a novel type of A??40 aggregate. In the absence of the nano-Au surface, the diameters of the A??40 fibrils were less than 10 nm. However, the height of the tubular aggregates formed on a nano-Au surface was 80?C100 nm. Such large-sized aggregates of A??40 have not been reported in previous studies dealing with interactions of suspended nanoparticles with proteins. This can be attributed to differences in the aggregation mechanism between immobilized and suspended nanoparticles. The formation of A??40 aggregates by nano-Au surface will provide the possible mechanism for abnormal fibril formation.     

Effect of protein fusion on the transition temperature of an environmentally responsive elastin-like polypeptide: a role for surface hydrophobicity?

The limited throughput, scalability and high cost of protein purification by chromatography provide motivation for the development of non-chromatographic protein purification technologies that are cheaper and easier to implement in a high-throughput format for proteomics applications and to scale up for industrial bioprocessing. We have shown that genetic fusion of a recombinant protein to an elastin-like polypeptide (ELP) imparts the environmentally sensitive solubility property of the ELP to the fusion protein, and thereby allows selective separation of the fusion protein from Escherichia coli lysate by aggregation above a critical temperature (T(t)). Further development of ELP fusion proteins as widely applicable purification tools necessitates a quantitative understanding of how fused proteins perturb the ELP T(t) such that purification conditions (T(t)) may be predicted a priori for new recombinant proteins. We report here the effect that fusing six different proteins has on the T(t) of an ELP. A negative correlation between T(t) and the fraction hydrophobic surface area on the fused proteins was observed, which was determined from computer modeling of the available three-dimensional structure. The thermally triggered aggregation behavior of ELP-coated, functionalized gold colloids as well as ligand binding to the tendamistat-ELP fusion protein support the hypothesis that hydrophobic surfaces in molecular proximity to ELPs depress the ELP T(t) by a mechanism analogous to hydrophobic residue substitution in the ELP repeat, Val-Pro-Gly-Xaa-Gly.     

Effects of thermal airflow and mucus-layer interaction on hygroscopic droplet deposition in a simple mouth–throat model

Hygroscopic growth of inhaled aerosols plays an important role in determining particle trajectories and hence local deposition sites. Accurate predictions of airway temperature and humidity as well as droplet–vapor interaction are critical for the calculation of hygroscopic growth. Employing a simple mouth–throat (MT) model as a computer simulation test bed, the effects of interactive heat transfer between air–droplet flow and mucus-tissue-layer have been analyzed. For a steady inhalation flow rate of 15?L/min, air temperature and relative humidity distributions affecting droplet growth, deposition efficiency (DE), and deposition pattern have been compared for different thermal airway-wall conditions. The effects considered include: (i) the latent heat of mucus-layer evaporation and convection heat transfer; (ii) convection heat transfer only; and (iii) mucus-tissue layer with constant temperature. As the most important outcome, the validated modeling results show that thermal airflow and mucus-layer interaction can significantly reduce hygroscopic growth and thereby decrease the DE of multicomponent droplets up to 10%. The modeling framework presented can be readily expanded to other systems.

Copyright © 2018 American Association for Aerosol Research     

Development of a filtered interphase heat transfer model based on fine-grid simulations of gas–solid flows

The filtered interphase heat-transfer coefficient for coarse-grid simulations of gas–solid flows can be obtained via a correction (Q) to its microscopic counterpart. The numerical results show that a good linear correlation between Q and the subgrid drift temperature exists at various filtered solid volume fractions, filter sizes and Reynolds numbers, where the subgrid drift temperature is the correlation between the fluctuating temperature of the gas phase and the fluctuation of the gas volume fraction. Since Q can be determined solely by one subgrid quantity, closure for Q is directly pursued. It is found that Q correlates surprisingly well with the product of the filtered solid volume fraction and the filtered temperature difference between the two phases normalized by the filtered heat transfer at a larger scale than the considered coarse grid. A fitting correlation is formulated based on this observation, and its predictability is evaluated in an a priori test.     

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field:Simulation on droplet coalescence☆

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as wel as its distribution, local concentration distribution and droplet size-velocity relation with the applied time of electric field. The sim-ulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.     

Fundamental studies on the hydrodynamics and mixing of gas and solid in a downer reactor

The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in both risers and downers.When the flow is in the direction ofgravity(downer),the radial profiles of gas and particle velocity are more uniform than that inthe riser,the solids mixing is very small and the flow pattern approaches plug flow,while theflow is against gravity(riser),the solids backmixing significantly increase and the flow pattern isfar from plug flow.Among many of factors the flow direction has the largest influence onhydrodynamics and axial mixing of gas and solids.     

Effect of titanium–magnesium catalyst morphology on the properties of polypropylene upon propylene polymerization in a liquid monomer

The effect of the particle size of an IK-8-21 domestic titanium-magnesium catalyst on the properties of polypropylene (PP) produced during the polymerization of propylene in a liquid monomer is studied. Catalysts with particle sizes of 20 to 64 μm are shown to have high activity and identical sensitivity to hydrogen and allow PP to be obtained with a narrow distribution of particles over size, high isotacticity, and close values of crystallinity, melting temperature, and physicomechanical properties. A slight decrease in the activity and bulk density of PP powder is observed when the average size of catalyst particles is increased from 20 to 43 μm. A more notable reduction in the activity and bulk density of PP powder is observed for catalyst with particle sizes of 62 to 64 μm. IK-8-21 catalyst is not inferior to its foreign analogues with respect to the properties of the resulting PP.     

High and low surface area NiO–MgO and CoO–MgO solid solutions: a study of XPS surface composition and CO oxidation activity

Oxide solid solutions NiO–MgO of high surface area were studied by XPS. The surface Ni²⁺ concentration was found to be equal, within experimental errors, to the bulk concentration. The result is analogous to that found previously for the low surface area NiO–MgO system and for both the high and low surface area systems of CoO–MgO. The catalytic oxidation of CO by O₂, on high and low surface area NiO–MgO and CoO–MgO materials, was investigated with the aim of relating the catalytic activity with transition metal ion nature and concentration. Turnover frequency data (CO₂ molecules produced per second per surface atom) show that the activity is due primarily to the transition metal ions and is not subject to the ions being in special configurations (dimers or trimers) or in special positions (edges, corners). The activity of CoO–MgO is higher than that of NiO–MgO solid solution. This revised version was published online in June 2006 with corrections to the Cover Date.     

What makes a dangling bond a binding site for thermal CH3 radicals? — A combined molecular dynamics and potential energy analysis study on amorphous hydrocarbon films

Identification of dangling bonds on amorphous films is not as straight forward as in the case of crystalline materials. The task is further complicated in the case of amorphous hydrocarbon (a-C:H) films by the existence of a wide variety of atomic arrangements. We present a technique based on potential energy analysis of a-C:H films to identify dangling bonds and physisorption sites. However, molecular dynamics simulations of the sticking of thermal CH₃ on a-C:H surfaces show that not all dangling bonds are binding sites for a CH₃ radical. Furthermore, the total sticking coefficient of the surface is not solely linked to the number of dangling bonds and can even decrease for the same number of dangling bonds because the carbon atoms that possess a binding site, active carbon atoms, show drastically different reactivity towards CH₃. The reactivity of active carbon atoms is decided by (a) their type, which is decided by the bonding partners, (b) their distance from the local surface and (c) the local environment. The reactivity of the active carbon atoms can be largely increased by energetic ion bombardment due to hydrogen depletion and local rearrangement.     

A study of adhesive improvement of a Cr–Ni alloy layer on a polyimide surface by low pressure gas plasma modification

The influence of low pressure oxygen (O₂) and argon (Ar) gas plasma modification of polyimide film on the adhesion to an alloy plating layer made from chromium (Cr) and nickel (Ni) was investigated. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were employed, respectively, to estimate the chemical and morphological status of the modified polyimide surface. Attenuated total reflectance-Fourier transform infrared (ATR-IR) spectroscopy and scanning electron microscopy (SEM) were also employed to determine the fracture mode during an adhesion durability test. The results indicated that O₂ plasma treatments generated carboxyl groups, but an excess of carboxyl groups could oxidize the Cr at the interface at elevated temperatures, which led to a loss of adhesion.     

Effects of surface initial condition on aqueous corrosion of glass—A study with a model nuclear waste glass

Being a nonequilibrium material, the structure of glass varies with the sample history. Thus, the initial surface condition of a glass can vary with the preparation condition and have a large impact on its reactivity. This paper shows that the aqueous corrosion behavior of international simple glass (ISG) varies depending on the initial surface state. The ISG glass samples were prepared as-polished-only and polished-then-annealed and they were immersed in aqueous solution saturated with soluble SiO₂ at 30°C (modeling a mild condition) and at 90°C (modeling a severe condition). Molecular dynamics simulations were performed to obtain coordination numbers of network formers of ISG to assist oxygen speciation calculations. The surface structures of as-prepared and corroded ISG samples were analyzed using various imaging and spectroscopic techniques. Among these analyses, only the oxygen speciation with x-ray photoelectron spectroscopy showed discernable differences between two uncorroded surfaces with different preparation histories; all other methods could not differentiate the surface preparation history before aqueous corrosion. Such minor difference in chemical structures was found to have a profound impact on corrosion behaviors in the mild condition. In the harsh condition, the surface history dependence was not as drastic as the corrosion in the mild condition. The analysis results of the corroded surfaces suggested that the thickness and structure of the alteration layer formed on ISG in aqueous corrosion can vary with the initial surface state.     

Effect of surface microstructure of TiO₂ film from micro-arc oxidation on its photocatalytic activity: a HRTEM study

Photocatalysis is a reaction that happens on the surface of catalysts around only several atomic layers. Therefore, the microstructure beneath the surface plays a key role for the improvement of photocatalytic property. In this paper, the microstructural variation of the TiO(2) film from micro-arc oxidation (MAO) was characterized by using a high resolution transmission electron microscopy (HRTEM), and the relationship between microstructures and photocatalytic activity was studied. The results revealed that: 1) The microstructural variation from the surface to the interior in the as-prepared film is as follows: an amorphous layer with thickness around 10-20 nm, an intermediate zone consisting of amorphous, anatase and few rutile TiO(2) phases with grain size about 12 nm, then the main structure consisting of anatase and few rutile TiO(2) phases with grain size around 20 nm. This variation was formed due to temperature gradient during MAO. 2) When the TiO(2) film was annealed at 450 °C for 12 h, the amorphous layer disappeared and crystallized into fine anatase grains, and, simultaneously, the grain size in the intermediate layer grew obviously from 12 nm into 18 nm, and the interior portion from 20 nm into 30 nm. 3) The photocatalysis experiments exhibited that photocatalytic activity of the post-annealed TiO(2) film was enhanced to more than twice that of the as-prepared TiO(2) film. Therefore, we propose that the crystallization of amorphous phase beneath the surface plays a key role for the improvement of its photocatalytic property.     

Effects of the pretreatment of a cemented carbide surface on its properties and on the properties of diamond coatings deposited by oxygen–acetylene flame CVD

The influence of the pretreatment of the WC (6% Co) surface on its properties (i.e. roughness, grain size and chemical composition) and on the properties of flame-deposited coatings have been studied. The surface treatments included the action of an oxidizing oxygen/acetylene flame at 1000 °C, scratching with diamond particles (14–20 μm), mixture with iron (<45 μm) in an ultrasound bath, and seeding with a nm-sized diamond suspension. An acid treatment was included in the pretreatment sequence. It is found that the oxidizing flame and the seeding decrease the surface roughness of the substrate as well as the diamond coatings, at the same time increasing the adhesion of the coating. Ultrasound scratching with the diamond/iron suspension increases the roughness of both the substrate and the diamond coating and decreases the adhesion of the coating. Scratching with diamond particles shows a similar but lesser effect. Except for scratching with diamond, all the surface pretreatment procedures lead to an increase in the density of diamond particles: this increase is greatest for seeding. Our results indicate that good adhesion and a small surface roughness are best obtained by the use of an oxidizing flame followed by acid treatment and seeding with nanoparticles.