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We investigated the magnetorheological (MR) properties of the carbon nanotube (CNT)-Co0.4Fe0.4Ni0.2 composite suspension to find a high-performance MR fluid with excellent stability. The composites were fabricated by chemical reduction of Co0.4Fe0.4Ni0.2 on the surface of amine-functionalized CNTs. A synergistic effect between the high aspect ratio of the CNTs and the strong magnetic polarization of the Co0.4Fe0.4Ni0.2 led to stronger MR performance of the nanocomposite particle suspension. The MR fluid exhibits an unexpected high yield stress value that is 13 times greater than that of a CNT-Fe3O4 suspension at a magnetic field strength of 343 kA/m. Nonmagnetic CNTs form a three-dimensional networklike structure, imparting surprisingly large additional yield stress to the CNT-Co0.4Fe0.4Ni0.2 nanocomposite MR suspension. The low density of the CNTs resulted in much better long-term stability for the CNT-Co0.4Fe0.4Ni0.2 nanocomposite suspension than the MR fluid containing only Co0.4Fe0.4Ni0.2.

A cellulose nanocrystal (CNC) sample with an average particle length and width of 170 and 7.8 nm, respectively, that was prepared from chemical pulp via sulfuric acid hydrolysis procedures was used...

Polydopamine (PDA)-Au Janus particles were obtained by simply adding HAuCl4 to a PDA particle suspension, prepared via self-polymerization of dopamine in basic solution at room temperature. The structures of the PDA-Au particles are readily controlled by electrostatic repulsion between the constituent particles, which can be realized simply via adjusting the environmental pH. PDA-Au Janus particles are formed only in a narrow pH range of 2.5-3.0 due to the properly enhanced electrostatic repulsion between the Au particles growing on as-prepared PDA particles and between the Au and PDA particles. The obtained PDA-Au Janus particles can become interfacially active and self-assemble at oil/water interfaces as a result of spatially well-separated hydrophilic (PDA) and hydrophobic (Au) domains on the surfaces, reminiscent of amphiphilic molecules. Refereed/Peer-reviewed

We develop a novel patterning technique to create 3D patterns of micro and nanoparticle assembly via evaporative self-assembly based on the coffee-ring effect of an evaporating suspension. The principle of the technique is analyzed theoretically by the scaling analysis of main parameters of the process and the scaling effect, the effect of the volume, the concentration of the suspension, and the effect of surface treatment on the patterning are studied. On the basis of the presented technique, we demonstrate that the patterns of 3D assembly of various sizes of microparticles (Silica), metal oxide nanoparticles (TiO(2), ZnO), and metallic nanoparticles (Ag) can be successfully generated by low-concentrated particle suspension (1.25-5 wt %) without additional sintering steps, and we also show the geometries of the patterns can be finely controlled by adjusting the parameters of the process.

The effect of the temperature on the dynamic behavior of PMMA−PHSA hard spheres under the influence of external electric field is described. By using a very uncommon light scattering setup for low ...

In this Article, we report the application of the quartz crystal microbalance (QCM) to study the evaporation of colloidal suspension droplets. Droplets of alumina particle suspensions with varying particle size and solid concentration have been investigated. Characteristic responses of the resonance frequency of the QCM associated with the different evaporation stages have been established. Quantitative analysis of the experimental results has been performed by the proposed QCM models. An interesting finding is that frequency increase after complete drying has been observed in some cases. Interpretation of the frequency increase has been developed in terms of the contact stiffness. The possible physical mechanisms are also discussed and quantified in terms of various interparticle forces.

The self-diffusion of water and a small and a large poly(ethylene glycol) (PEG) were monitored during the sol−gel transition of a casein system induced by chymosin action using pulsed field gradien...

A theory of nanoparticle dynamics based on scaling arguments and the Liouville equation is presented. We start with a delineation of the scales characterizing the behavior of the nanoparticle/host fluid system. Asymptotic expansions, multiple time and space scale techniques, the resulting coarse-grained dynamics of the probability densities of the Fokker-Planck-Chandrasekhar (FPC) type for the nanoparticle(s), and the hydrodynamic models of the host medium are obtained. Collections of nanoparticles are considered so that problems such as viral self-assembly and the transition from a particle suspension to a solid porous matrix can be addressed via a deductive approach that starts with the Liouville equation and a calibrated atomic force field, and yields a generalized FPC equation. Extensions allowing for the investigation of the rotation and deformation of the nanoparticles are considered in the context of the space-warping formalism. Thermodynamic forces and dissipative effects are accounted for. The notion of configuration-dependent drag coefficients and their implications for coagulation and consolidation are shown to be natural consequences of the analysis. All results are obtained via formal asymptotic expansions in mass, size, and other physical and kinetic parameter ratios.

Coal extract and suspensions of coal particles are capable of forming viscoelastic gels. The nature of the connections or interactions in these systems is not clear. Simple experiments reported in this article indicate that NMP/CS2 extracts from Upper Freeport coal are predominantly solutions of molecular species that nevertheless form gels at certain concentrations. The physical gels formed in these mixtures must therefore involve some specific association that, in turn, can lead to aggregation, such as π-cation interactions, or a phase separation. This latter mechanism must involve bicontinuous domains where one of the phases is glassy, to provide the cohesive properties necessary for elastic properties. In contrast, gels formed from insoluble coal particles most probably associate through forces common to many colloidal suspensions. In such systems, it is not the local pairwise interactions between molecules alone that is important, but the sum of all interactions between the molecules in each particle...

The interaction between spherical particles covered with end-grafted polymers (brushes) immersed in a polymer melt is studied theoretically. It has been known for some time that two densely grafted brushes may attract each other in the presence of a chemically identical polymer melt. In this study we show that this attraction can be eliminated by choosing the melt material to be such that the Flory interaction parameter of the melt chains with the grafted ones is negative (χ < 0). This effect is accompanied by a change in the structure of the brush from a dry brush, where the melt chains do not penetrate deeply into the brush, to a wet brush, where the melt chains penetrate the brush and force the grafted chains to extend into the melt. Scaling arguments are used to describe how the structure of a single brush depends on the Flory interaction parameter, the grafting density, and the indices of polymerization of the grafted and free chains. The density profiles and the interactions between the particles ar...

According to the dielectric design, a new kind of rare-earth (RE)-doped TiO2 particle was synthesized by means of sol−gel technique for use in electrorheological (ER) fluids. A distinct enhancement...

The bifunctional phosphine Ph2P(CH2)3Si(OEt)3 has been immobilized on MgO, TiO2, Al2O3, and SiO2 surfaces. The materials were studied by 27Al MAS, 29Si CP/MAS, 31P CP/MAS, and 31P suspension NMR sp...

Electro-osmotic dewatering (EOD) of 9.1 wt % bentonite slurry was investigated using a stationary and rotating anode. The rotational speed varied from 0 to 300 rpm. Excessive slurry is necessary to...

The structures of water, partitioned in cation-exchange resin particles, were studied on the basis of fluorescence dynamics of Nile Blue A (NB). The fluorescence lifetime of NB in the resin was longer than that in water and increased with increasing cross-linking density of the resin (rho). The results demonstrated that the water structures in the resin were significantly different from those in water and dependent on rho. A study on solvation dynamics of NB in the resin, reflecting structured water around the ion-exchange group, revealed the roles of "bound water" molecules in the water structures, since the solvent relaxation time (tauS) in the resin was much longer than that in water and depended on p; tauS increased from 34 to 55 ps with increasing rho from 2 to 8%. The origin of the rho dependence of tauS was discussed in terms of the separation distance between the ion-exchange groups, and the effects of the counterion of the ion-exchange group on the solvation processes were also discussed.

A simple model of the breakup of a floc in a turbulent flow is proposed by analogy with that of a droplet. In the model, the strength of a floc is expressed as a product of the cohesive force betwe...

The behavior of suspensions in settling and compression is fully defined by two parameters: the compressive yield stress function Py(φ) and the hindered settling function r(φ). The compressive yie...

A detailed model for a wet flue gas desulfurization (FGD) pilot plant, based on the packed tower concept, has been developed. All important rate-determining steps, absorption of SO2, oxidation of H...

A new strategy to create well-ordered latex particle monofilms from polydisperse latex solutions was developed. Due to size-dependent segregation, the spherical particles assemble in grains with a uniform sphere size within each grain. The size-dependent segregation process can be deduced from the action of a single force, the lateral capillary force. A strong temperature dependence can be observed, and the process becomes evident when the substrate is cooled. The samples are characterized by scanning force microscopy. Finally, to prove the theoretical model, a computer simulation is performed, supporting the experimental results.

Adsorption of cationic surfactants (dodecyltrimethylammonium bromide, 1RQ; 1,2-bis(dodecyldimethylammonio)ethane dibromide, 2RenQ) has been investigated on titanium dioxide with a dodecyl chain anchor. The adsorbed amounts of 1RQ and 2RenQ increase with increasing concentration of the dodecyl chain anchor on titanium dioxide, where the adsorbed amounts of 1RQ at saturation are considerably greater than those of 2RenQ. Changes in the dispersion stabilities and the ζ potentials of the titanium dioxide suspensions are well correlated with the adsorption behaviors of the surfactants. The adsolubilized amounts of 2-naphthol in the surfactant-adsorbed layer also increase with increasing concentration of the dodecyl chain anchor for 1RQ and 2RenQ, whereas those with 2RenQ are greater than those with 1RQ even though there is a smaller amount of adsorbed 2RenQ. These differences in the adsolubilization are attribued to the surfactant compactness in the adsorbed layer estimated by ESR.

Microbial transformations were conducted with prosulfuron {1-(4‘-methoxy-6‘-methyltriazin-2‘-yl)-3-[[2‘‘-(3‘‘‘,3‘‘‘,3‘‘‘-trifluoropropyl)phenyl]sulfonyl]urea} to identify pathways by which the sulf...

A new way to construct small electrodes by the use of metal microbeads is described. Gold beads of 1.5−3.0 μm diameter were used to construct inexpensive and disposable microelectrodes with overall structural diameters of ≤6 μm and electrode diameters of ≤5 μm. The voltammetric response of these electrodes is consistent with existing theory, and the electrodes exhibited the sigmoidal waves expected at ultramicroelectrodes.

We study the bimolecular coagulation A + A → A and annihilation A + A → 0 reactions with diffusion and probability p of reaction in one dimension and annihilation reaction with diffusion and short range interactions in two-dimensional fractal and nonfractal percolation clusters. In these cases there is no input of particles and the particle density Ρ decays as a function of time t. The effect of p and interactions become relevant at short times. In one dimension analytical approximations of the density for coagulation and annihilation reactions are found which agree very well with Monte Carlo results of Ρ(t) for all times and for small values of p. For percolation clusters and large values of the nearest-neighbor repulsive interaction Ubetween particles, we find that a simple mean-field approximation works at short times. The length of the interval where this approximation holds increases as U increases. For the case of repulsive nearest-neighbor with attractive next nearest-neighbor interactions we find an exponential decay of the density at short times. We also analyze the steady-state regime of annihilation and coagulation reactions ofimmobile reactants with reaction probability and input of particles in a one-dimensional lattice. Analytical approximations of the particle density and of the n-particle correlations are obtained. The limit of zero input rate is solved exactly. The analytical results were confirmed by Monte Carlo simulations.

In dilute solution, semicrystalline diblock copolymers with one crystallizable block form thin platelet structures consisting of a chain-folded crystalline domain between solvated layers of the amo...

The problem of reaction kinetics in microdisperse systems undergoing collisional exchange is addressed. The migration of reactants is suggested to occur as successive one-particle hopping through fluctuational channels between the droplets during their collisions with temporary merging. The redistribution dynamics within the droplet encounter pair are described using a stochastic approach. The resulting transition probability is calculated as a function of the hopping frequency and the characteristic lifetime of the connecting channels. A hopping mechanism for collisional exchange is employed in analyzing migration-assisted time-resolved luminescence quenching. Applications to fluorescence stopped-flow experiments are also discussed

Multicomponent solid particles were suspended in vertical bubble columns of 7-cm diameter and 4.85-m height and 15-cm diameter and 2.7-m height. Axial changes in holdups of gas and solids in the column were determined by sectioning the column simultaneously with 20 horizontal plates for the 7-cm-diameter column and 11 such plates for the 15-cm-diameter column. Solid particles used were sieved glass beads (118, 243, and 465 μm) and mixtures thereof. A one-dimensional sedimentation-dispersion model was applied to describe the axial holdup profile of each solid component. The parameters used in the model were all correlated with experimental equations based on the results of single-component systems