Dispersion Of Small Particles Research Articles

Self-suspended suspensions of covalently grafted hairy nanoparticles.

Dispersions of small particles in liquids have been studied continuously for almost two centuries for their ability to simultaneously advance understanding of physical properties of fluids and their widespread use in applications. In both settings, the suspending (liquid) and suspended (solid) phases are normally distinct and uncoupled on long length and time scales. In this study, we report on the synthesis and physical properties of a novel family of covalently grafted nanoparticles that exist as self-suspended suspensions with high particle loadings. In such suspensions, we find that the grafted polymer chains exhibit unusual multiscale structural transitions and enhanced conformational stability on subnanometer and nanometer length scales. On mesoscopic length scales, the suspensions display exceptional homogeneity and colloidal stability. We attribute this feature to steric repulsions between grafted chains and the space-filling constraint on the tethered chains in the single-component self-suspended materials, which inhibits phase segregation. On macroscopic length scales, the suspensions exist as neat fluids that exhibit soft glassy rheology and, counterintuitively, enhanced elasticity with increasing temperature. This feature is discussed in terms of increased interpenetration of the grafted chains and jamming of the nanoparticles.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ВЗАИМОДЕЙСТВИЯ ЭЛЕКТРОМАГНИТНОГО ПОЛЯ С МАЛЫМИ ДИСПЕРСНЫМИ ЧАСТИЦАМИ РАЗЛИЧНОЙ ГЕОМЕТРИИ И ИХ ДИНАМИКИ

The model of the electromagnetic waves interaction with small particles and clusters is proposed in the case when the dielectric permittivity of the material depends both on the electric and magnetic fields. We consider the class of the differential equations solutions that is obtained in the framework of the model and allows take into account the geometric structure of the small dispersed particles or clusters. The motion and precipitation of water clusters in narrow tubes is investigated by molecular dynamics methods.

The Effect of Platinum in the Membrane on Fuel Cell Membrane Durability

Development of highly durable fuel cell membranes is essential to achieve the heavy duty fuel cell bus lifetime targets. The bus duty cycle exposes fuel cell membranes to conditions that can eventually lead to membrane degradation, and limit fuel cell lifetime. Fuel cell membranes can degrade both chemically and mechanically leading to membrane thinning, as well as pinhole and crack formation over time. Chemical degradation occurs primarily due to radical attack of the membrane. It has been observed that during bus operation, platinum particles migrate into the membrane due to catalyst degradation, forming a distinguishable band close to the cathode [1]. The presence of platinum in the membrane (PITM) is known to affect membrane durability. Observations of both negative and positive effects have been reported in the literature [2-5]. The platinum particle size and distribution inside the membrane have been found to be important factors. A low concentration of highly dispersed small particles is believed to result in increased degradation, and on the other hand a Pt band in the membrane with higher Pt concentrations was confirmed to be effective to improve durability [1]. The effect of PITM on membrane degradation is investigated by deliberately generating a platinum band in the membrane and running an in situ Accelerated Membrane Durability Test (AMDT) on fuel cells containing such membranes. The lifetime of reference baseline cells, without intentionally deposited PITM is compared to the lifetime of cells with PITM under AMDT conditions. Our results confirm that the presence of PITM prolongs membrane lifetime, suggesting that PITM is able to decrease membrane chemical degradation, either by decomposing H2O2 (to non-radical products) and/or converting crossover gases to water at the Pt band, thus avoiding radical formation. It was also found that higher PITM concentrations result in a longer membrane lifetime. In addition, membranes with PITM show no thinning, while the baseline membranes show severe membrane thinning after being exposed to the same AMDT conditions. Ex situ mechanical tests on AMDT degraded baseline membranes show significantly reduced mechanical strength of the membranes without PITM. Again, the mechanical strength of the membranes with PITM is on the other hand highly preserved. These findings support the theory that the platinum band mitigates membrane chemical degradation under the conditions tested. However, it is important to understand the precise structure of the particles located in the Pt band. Thorough analysis of these Pt particles will help improve the general understanding of the lifetime enhancing effects of PITM. Therefore a systematic characterization procedure of the end-of-life AMDT membranes is conducted using transmission electron microscopy (TEM). The Pt particle sizes, distribution, distances between particles and Pt crystallinity are reported, and their role in the mitigation mechanism is discussed.AcknowledgmentsThis research was supported by Ballard Power Systems and the Natural Sciences and Engineering Research Council of Canada through an Automotive Partnership Canada (APC) grant.[1] Macauley, N., Ghassemzadeh, L., Lim, C., Watson, M., Kolodziej, J., Lauritzen, M., Holdcroft, S., and Kjeang, E. (2013). ECS Electrochem. Lett, 2(4), F33-F35.[2] Rodgers, M. P., Bonville, L. J., & Slattery, D. K. (2011). ECS Trans., 41(1), 1461-1469.[3] Helmly, S.,Ohnmacht, B., Hiesgenc, R., Gülzowa, E., and Friedrich, K. A. (2013) ECS Trans., 58 (1) 969-990.[4] Rodgers, M. P., Pearman B. P., Bonville L. J., Cullen D. A., Mohajeri N., and Slattery, D. K. (2013). J. Electrochem. Soc., 160(10) F1123-F1128. [5] Gummalla, M., Atrazhev, V. V., Condit, D., Cipollini, N., Madden, T., Kuzminyh, N. Y., Weiss, D., Burlatsky, S. F. (2010). J. Electrochem. Soc. 157, B1542.

Enhancing the Flexural and Impact Properties of Bioplastic Poly(lactic acid) by Melt Blending with Poly(butylene succinate)

Bio-based biodegradable Poly (lactic acid) (PLA) suffers limitations such as brittleness and slow crystallization. This study aims to resolve the brittle nature of PLA by blending with Poly (butylene succinate) (PBS), a more ductile biodegradable polymer with superior toughness and flexural properties. In this research, a series of PLA/PBS blends was prepared at the blend ratios of 100/0, 80/20, 60/40, 40/60, 20/80 and 0/100. FTIR showed that there was no change in the functional groups of the PLA/PBS blends. Thermal stability assessed by TGA revealed that PBS degraded at higher temperature than that of PLA; the decomposition temperature (Td) at 10% weight loss of PLA and PBS were 330.8 and 356.4°C respectively. The Td of all the blends increased gradually with the addition of PBS. The flexural properties in terms of the flexural strength and the flexural modulus of the blends reduced significantly with PBS content. The PLA/PBS specimens with greater PBS content were softened and flexed more easily, thereby requiring a much lower flexural strength. The flexural modulus of the 80/20 and 60/40 blends dropped from 3.5 GPa for neat PLA to 3.2 GPa and 2.1 GPa while the flexural strength also declined from 105.3 MPa to 90.9 MPa and 69.1 MPa respectively. The toughness of all the blends was greater than that of neat PLA; in particular the 60/40 blend exhibited superior impact strength of 48.7 J/m compared with 30.9 J/m of the neat PLA. The microscopic images of all the blends showed two distinct phases; the 60/40 blend consisted of well dispersed small particles of the tough PBS, resulting in greater absorption of energy upon impact.

Characteristics of droplet motion in effervescent sprays

Time resolved droplet size and velocity measurement was made using Phase-Doppler anemometry in an effervescent spray at GLR of 6 % and operation pressure drops 21 – 52 kPa. The spray shows a size dependent variation of mean as well as fluctuating axial and radial velocities of droplets similarly for all operation regimes. Particles under 13 μm follow the gas flow, axially decelerated due to gas expansion. Velocity of medium sized particles is positively size correlated and larger particles keep high velocity, given them during discharge. Fluctuating radial velocity of small particles is larger than that of large particles while fluctuating axial velocity increases with size. Small particles thus reach a ratio of radial to axial velocity fluctuations ~ 0.6 but large particles only ~ 0.1, which indicates large transverse dispersion of small particles. Overall fluctuating velocity ratios smaller than 0.5 document an anisotropic character of the liquid mass fluctuations. Power spectral density (PSD) of axial velocity fluctuations of large droplets is uniform up to 1 kHz, while PSD of smaller particles drops down with frequency for frequencies > 100 Hz. Large particles thus preserve the fluctuations imposed during discharge while the gas turbulence drops with frequency. Turbulence intensity reaches 14 to 21 % depending on pressure. Such high-turbulence character of the flow probably results from a heterogeneous gas–liquid mixture at the discharge.

Effect of pre-irradiation PPO-grafted maleic anhydride on structure and properties of PPO-g-MAH/PA66 blends

The pre-irradiation polyphenylene oxide (PPO)-graft-maleic anhydride (PPO-g-MAH) was carried out by reactive extrusion. The chemical structure of PPO-g-MAH was characterized by means of Fourier-transform infrared spectroscopy. The wettability of PPO-g-MAH was characterized by the contact angle method. The blends of PPO-g-MAH/polyamide 66 (PA66) were prepared. Compared with the PPO/PA66 blends, mechanical properties of PPO-g-MAH/PA66 blends were distinctly improved. Smaller dispersed particle sizes with narrower distribution were found in PPO-g-MAH/PA66 blends, via field-emitted scanning electron microscopy. Rheological properties of PPO-g-MAH/PA66 blends were studied with a rotational rheometer.

Bifurcation from stable holes to replicating holes in vibrated dense suspensions

In vertically vibrated starch suspensions, we observe bifurcations from stable holes to replicating holes. Above a certain acceleration, finite-amplitude deformations of the vibrated surface continue to grow until void penetrates fluid layers, and a hole forms. We studied experimentally and theoretically the parameter dependence of the holes and their stabilities. In suspensions of small dispersed particles, the circular shapes of the holes are stable. However, we find that larger particles or lower surface tension of water destabilize the circular shapes; this indicates the importance of capillary forces acting on the dispersed particles. Around the critical acceleration for bifurcation, holes show intermittent large deformations as a precursor to hole replication. We applied a phenomenological model for deformable domains, which is used in reaction-diffusion systems. The model can explain the basic dynamics of the holes, such as intermittent behavior, probability distribution functions of deformation, and time intervals of replication. Results from the phenomenological model match the linear growth rate below criticality that was estimated from experimental data.

Phase Morphology, Thermal and Mechanical Properties of Compatibilized Nylon12/Natural Rubber Blends Using PS/MNR

To produce a tough material for application demanding high impact resistance and low moisture absorption, melt blending of Nylon12 (Polyamide 12, PA12) and natural rubber (NR) was carried out in a brabender plasticorder at 210 °C with rotor speed of 70 rpm in the presence of polystyrene/maleated natural rubber (PS/MNR) blend as a compatibilizer. The effect of compatibilizer content (1, 3, 5, 7 and 10 phr) on phase morphology, thermal, and mechanical properties of [Nylon12/NR]/[PS/MNR] blends was investigated by using SEM, DSC, and Izod impact tester, respectively. The result revealed that PS/MNR blend improved the compatibility of Nylon12/NR blends efficiently due to the presence of amide linkage at the interfaces from the reaction between the reactive groups of MNR and the NH2 end groups of Nylon12 during mixing. A fine phase morphology (good dispersion and small dispersed phase size of NR domains in Nylon12 matrix) of [Nylon12/NR]/[PS/MNR] blends was observed at the optimum compatibilizer content of 7 phr, relating to the improvement of mechanical property. The impact energy of [Nylon12/NR]/[PS/MNR] blends was 503 J/m higher than that of neat Nylon12 (115 J/m) and Nylon12/NR binary blend (241 J/m) due to the toughening effect of rubber and proper morphology. The melting temperature of all blends did not change obviously from thermal analysis. However, the presence of rubber particle obstructed the crystallization of Nylon12 phase, leading to the decreasing of %crystallinity from 93% to around 70%.

Role of Pt in the Activity and Stability of PtNi/CeO2–Al2O3 Catalysts in Ethanol Steam Reforming for H2 Production

Hydrogen production from ethanol reforming was investigated on bimetallic PtNi catalysts supported on CeO2/Al2O3. Pt content was varied from 0.5 to 2.5 %. Physico-chemical characterization of the as-prepared and H2-reduced catalysts by TPR, XRD and XPS showed that Pt phase interacted with the Ni and Ce species present at the surface of the catalysts. This interaction leads to an enhancement of the reducibility of both Ni and Ce species. Loadings of Pt higher than 1.0 wt% improved the activity and stability of the Ni/CeO2–Al2O3 catalyst in ethanol steam reforming, in terms of lower formation of coke, C2 secondary products and a constant production of CO2 and H2. The amount and type of carbon deposited on the catalyst was analyzed by TG–TPO while the changes in crystalline phases after reaction were studied by XRD. It was found that for Pt contents higher than 1 wt% in the catalysts, a better contact between Pt and Ce species is achieved. This Pt–Ce interaction facilitates the dispersion of small particles of Pt and thereby improves the reducibility of both Ce and Ni components at low temperatures. In this type of catalysts, the cooperative effect between Pt0, Ni0 and reduced Ce phases leads to an improvement in the stability of the catalysts: Ni provides activity in C–C bond breakage, Pt particles enhance the hydrogenation of coke precursors (CxHy) formed in the reaction, and Ce increases the availability of oxygen at the surface and thereby further enhances the gasification of carbon precursors.

Frederick Wells Leavitt: a pioneer in adsorption technology

Fred was born in Elizabeth, New Jersey in 1928. He attended Union Junior College from 1946 to 1948 and Newark College of Engineering from 1948 to 1950 (both in New Jersey) where he obtained his B.S. Ch.E. He then served in the US Army from 1950 to 1952, with subsequent employment with the US Army Chemical Corps. Fred was admitted to the Chemical Engineering Graduate Study Program at Rensselaer Polytechnic Institute (RPI) in 1954 and completed a M.S. Ch. E. in 1955 and his Ph.D. in June 1957 (Leavitt 1957). On his application for admission to graduate study at RPI, Fred indicated interests in ‘‘heterogeneous systems, especially those containing dispersions of small particles .... study of solid–liquid–vapor equilibria, heat and mass transfer mechanisms, reaction kinetics, and the motion of small particles in resisting media.’’ In the career that followed, Fred made significant contributions in all of these areas. Fred joined the Molecular Sieve Group at Linde Air Products Company (Division of Union Carbide Corporation) in 1957. This timing is particularly significant to the field of adsorption due to the following events of the 1950s:

Soft Iron/Silicon Composite Tubes for Magnetic Peristaltic Pumping: Frequency‐Dependent Pressure and Volume Flow

AbstractThe combination of force and flexibility enables controlled and soft movements. In sharp contrast, presently used machines are solid and mostly based on stiff driveshafts or cog wheels. Magnetic elastomers are realized through dispersion of small particles in polymer matrices and have attracted significant interest as soft actuators for controlled movement or conveying and are particularly attractive candidates for magnetic pump applications. At present, low magnetic particle loading and thus limited actuator strength have restricted the application of such materials. Here, the direct incorporation of metal microparticles into a very soft and flexible silicone and its application as an ultra‐flexible, yet strong magnetic tube, is described. Because metals have a far higher saturation magnetization and higher density than oxides, the resulting increased force/volume ratio afforded significantly stronger magnetic actuators with high mechanical stability, flexibility, and shape memory. Elliptical inner diameter shape of the tubing allowed a very efficient contraction of the tube by applying an external magnetic field. The combination of magnetic silicone tubes and a magnetic field generating device results in a magnetic peristaltic pump.

Improving Quality of High Performance Concrete by Cavitation Treatment of the Raw Materials

The packing of fine aggregate affects the properties of HPC. The denser is fine aggregate packing the better are the workability, compressive strength and watertightness, and with that the frost and chemical resistances under sufficient paste content upplementary cementing materials such as silica fume has predominantly used for HPC due to it improves the packing of the concrete mix and activates the pozzolanic reaction. But agglomerates can be formed in this fine aggregate mix and therefore the packing of the mix is not improved, chemical reaction is hindered and the use of this aggregate may worsen the concrete properties instead of improving them.The effect of cavitation treatment on silica fume and cement is investigated in this work. Due to cavitation treatment, the agglomerate of silica fume and cement collapses into nano- and micro-particles and uniforms dispersion of small dispersed particles in liquid medium. Granulometric composition of silica fume slurry before and after cavitation treatment was determined.High performance concrete mixes with designed packing including micro- and nano-size fillers were elaborated. Fresh and hardened concrete were tested and such properties as cone flow, watertightness, water absorption and compressive strength were defined for control and experimental mixes. The influence of cavitation treatment of small dispersed raw materials on the compressive strength properties of produced concrete has been evaluated.

A novel brush feeder for the pneumatic delivery of dispersed small particles at steady feed rates

Abstract A novel particle feeding system capable of pneumatically dispensing dispersed particles at low and consistent feed rates has been developed. The feeder is based on a rotating brush that continually cleans the outlet orifice in a hopper filled with particles. The system was designed specifically for biomass particles that have been milled and sieved to less than 150 μm as a feedstock for laboratory scale aerosol flow reactors. This feedstock often contains a large fraction of high aspect ratio particles that form obstructions in many conventional feeding systems. In addition to biomass, the feeder has successfully fed all particles less than 150 μm that have been tested. Feed rates varying from 4.25 to 2420 mg/min have been obtained with spray dried algae at a constant carrier gas flow of 0.75 slpm, and steady and consistent feeding with milled switchgrass has been demonstrated. The design, construction, and preliminary testing of the feeding system are presented in this paper.

Permanent antistatic polypropylene based on polyethylene wax/polypropylene wax grafting sodium acrylate

AbstractTwo types of permanent antistatic agents, polyethylene wax grafted with sodium acrylate (PEW‐g‐AAS) and polypropylene (PP) wax grafted with sodium acrylate (PPW‐g‐AAS), were prepared using a solution grafting method and applied to PP for enhancing antistatic properties. The grafting degree was determined using back titration method and structures were confirmed by Fourier transform infrared spectroscopy. The antistatic properties of PEW‐g‐AAS/PP blends and PPW‐g‐AAS/PP blends were characterized by surface resistivities (ρs) and volume resistivities (ρv), and a combination of contact angle measurements, scanning electron microscope, permittivity, and dielectric loss were used to investigate the surface and inner structures of the blends. Results showed ρs and ρv of PEW‐g‐AAS/PP blends dropped significantly (4–7 magnitudes) above a critical addition at 10%, where a electrostatic dissipative network formed; PPW‐g‐AAS revealed an inferior antistatic performance than PEW‐g‐AAS due to its better compatibility and smaller dispersed phase in the matrix. Further, the antistatic blends treated in 80°C water, 80°C air, and room temperature were investigated, and the results were interpreted from surface energy. Moreover, the addition of antistatic agent had little impact on tensile strength of the PP matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

In situ characterization of Ptcatalysts supported on ceria modified TiO2 for the WGS reaction: influence of ceria loading

This work analyzes the influence of cerium content (6-15 wt%) on a TiO(2) support over the structure and water gas shift (WGS) activity of Pt catalysts. The structural properties of these Pt/Ce-TiO(2) catalysts were characterized by XRD, TEM and XANES. Physicochemical characterization of the catalysts showed differences in the structure and dispersion of Ce entities on the support with Ce loading. For the samples with low ceria content (6 wt%), cerium is deposited on the support in the form of CeO(x) clusters in a highly dispersed state in close interaction with the Ti atoms. The formation of CeO(x) clusters at low Ce-loading on the support facilitates the dispersion of small particles of Pt and improves the reducibility of ceria component at low temperatures. The changes in platinum dispersion and support reducibility with Ce-loading on the TiO(2) support lead to significant differences in the WGS activity. Pt supported on the sample with lower Ce content (6 wt%) shows better activity than those corresponding to catalysts with higher Ce content (15 wt%). Activity measurements coupled with catalysts characterization suggest that the improvement in the reducibility of the support with lower Ce content was associated with the presence of CeO(x) clusters of high reducibility that improve the chemical activity of the oxide-metal interfaces at which the WGS reaction takes place.

Evaluation of Numerical Schemes for Dispersed Phase Modeling of Cyclone Separators

:This study investigates the performance of different discretization schemes for simulation of dispersed phase of cyclone separators by using Reynolds stress turbulence model facility of CFD code Fluent 6.3.26. The continuous flow inside the cyclone separator is simulated by solving Reynolds averaged three dimensional unsteady Navier-Stokes equation in Eulerian reference frame whereas the dispersed phase is modeled using Lagrangian approach. Analysis of computed results shows that the high order discretization schemes give satisfactory performance for simulation of dispersed particles of all size. However the prediction of trapezoidal discretization scheme is found to be marginally better than that of the Runge-Kutta scheme. The low order schemes and combination of low order and high order schemes failed to predict accurately the collection efficiency of the smaller dispersed particles. The results suggest that the CFD method using trapezoidal scheme for discretization of equation of motion of dispersed particles is the optimum choice for simulation of the second phase of cyclone separators.

Direct Evidence of Water-Assisted Sintering of Cobalt on Carbon Nanofiber Catalysts during Simulated Fischer−Tropsch Conditions Revealed with in Situ Mössbauer Spectroscopy

Cobalt on carbon nanofiber model catalysts with very small dispersed cobalt particles of 5 nm were subjected to H(2)O/H(2) treatments at 20 bar and 220 degrees C. Using in situ Mossbauer spectroscopy we could unambiguously prove that oxidation of the nanoparticles by water will not occur when hydrogen is present. Only in a water/argon atmosphere did oxidation take place. This rules out oxidation as the deactivation mechanism in Fischer-Tropsch synthesis. Even more important, we define the relative humidity (RH) as a key parameter to understanding deactivation by water. At a RH below 25% sintering was absent even when measuring for 4 weeks, whereas at a high RH of 62% as much as half of the small super paramagnetic cobalt particles (<5 nm) sintered into larger particles in 1 week. Activity loss as measured at Fischer-Tropsch conditions amounted to 73%, which could be directly related to the metal dispersion loss 77% due to sintering as evidenced by detailed TEM analysis of the spent sample.

Dynamics of PIV seeding particles in turbulent premixed flames

Particle image velocimetry (PIV) estimates the fluid velocity field measuring the displacement of small dispersed particles between two successive instants separated by a small time interval. The accuracy of the measurements depends on the ability of the particles to accommodate their velocity to the fluid fluctuations. When the fluid is subjected to extreme accelerations, the small but finite inertia prevents the particles from following the fluid, originating a substantial relative velocity. This effect is shown to be crucial for applications of PIV to turbulent premixed combustion, particularly in the product region at locations just behind the instantaneous flame front. The issuing inaccuracy may easily spoil the estimate of certain statistical observables which are of crucial importance in the theory of turbulent premixed combustion. By exploiting the direct numerical simulation of a model air/methane flame, a suitable criterion for proper particle seeding is validated and compared with the corresponding experiments with a combined PIV/OH-LIF (laser-induced fluorescence) system. The proposed parameter, the flamelet Stokes number, depends on particle properties and thermochemical conditions of the flame and substantially restricts the particle dimensions required for a reliable estimate of the relevant flow statistics.

Effect of Electric Current on the Inclusions in a Cu-Zn Alloy

The effect of electric current pulse (ECP) treatment on lead inclusions in a Cu-Zn alloy was studied in present work. It was found that with the application of a critical high current density, the coarse and random distributed lead inclusions transferred into grain boundaries or defects in dispersed small particles. The reason was ascribed to the specific electric effect of electric current on the grain refinement and the reduction of the diffusive activation energy of lead inclusions. Therefore, the high current density ECP treatment might be an effective method to refine inclusions of bulk materials.

Mechanisms of particle dispersion in a turbulent, square duct flow

AbstractParticle dispersion in a square duct flow is studied using large eddy simulation combined with Lagrangian particle tracking under conditions of one‐way coupling. The flow has a bulk Re = 250 k, with six particle sizes ranging from 5 to 1000 μm. Results obtained for the fluid phase show good agreement with experimental data. For particles, predictions demonstrate that secondary flows within the duct dominate small particle dispersion and result in a uniform distribution, whereas gravity promotes the deposition of large particles on the duct floor. For the largest particles, the secondary flows contribute to particle concentration in corners on the duct floor, with these particles also clustering in low‐velocity regions close to the floor. A detailed analysis of the influence of the flow on particle distribution is provided through consideration of the particle dispersion function, with the mechanisms of particle dispersion elucidated using a dynamical analysis. © 2009 American Institute of Chemical Engineers AIChE J, 2009