Thixotropic interparticle interaction between silica and nonionic polymer particles prepared by static dispersion polymerization

Static dispersion polymerization of styrene, methyl methacrylate, ethyl methacrylate, butyl methacrylate and benzyl methacrylate, initiated by a lipophilic initiator in an aqueous dispersion with unmodified silica particles was investigated. Polymerization of styrene gave a mixed dispersion of silica and monodisperse polystyrene (PS) particles, which was extremely stable compared with the aqueous dispersion of silica particles. The enhanced dispersion stability is due to a thixotropic effect based on weak attractive interparticle interactions between silica and PS particles in aqueous dispersion. An aggregate in which silica particles are surrounded by the smaller PS particles is formed and inhibits flocculation of silica particles, thus giving enhanced dispersion stability. The results of similar static polymerization reactions with methacrylate analogs indicate that hydrogen bonds between benzene ring and hydroxy groups on the silica surface, and not electrostatic interaction derived from initiator residues, are the origin of weak interaction for thixotropic aggregation.     

Mechanism for refunctionalizing heat-denatured soy protein by alkaline hydrothermal cooking

Using extrusion heat-denatured soy protein isolate (SPI) as a model, the mechanism for refunctionalizing heat-denatured soy protein by hydrothermal cooking (HTC) with alkali was studied. Heating causes soluble protein to form insoluble protein aggregates. Treating heat-denatured soy protein with alkali dispersion without HTC increased solubility and viscosity by dissolution of a portion of the protein aggregates and swelling of the large protein particles. This suspension was more stable to solid separation than that of the original untreated heat-denatured protein, but it was less stable than the protein suspensions that were refunctionalized by water dispersion with HTC or alkali dispersion with HTC. Water dispersion with HTC disrupted the large aggregates into smaller aggregates. The viscosity and total number of particles in the system also increased dramatically. The most significant effect was achieved with alkali dispersion (0.6 mmol NaOH/g) with HTC. The solubility increased from 4 to about 80% at neutral pH, and viscosity (at zero shear rate) increased by more than 1,000 times compared with extrusion heat-denatured SPI. Alkali dispersion (0.6 mmol NaOH/g) with HTC dissolved most of the protein particles, decreasing the particle number by a factor of almost 100. The suspensions of heat-denatured soy protein became much more stable after HTC as shown by particle settling velocities. The most effective treatment was alkali dispersion (0.6 mmol NaOH/g) with HTC, followed by water dispersion with HTC. The soy protein slurry refunctionalized by alkali dispersion (0.6 mmol NaOH/g) with HTC formed soft, translucent gels.     

Preparation of Highly Dispersed Ultrafine Barium Titanate Powder by Using Microbial-Derived Surfactant

To uniformly disperse ultrafine BaTiO₃ particles with a stoichiometric composition and several tens of nanometers in diameter to primary particles during the sol–gel synthesis process, a new aqueous surfactant with a high hydrophilic group density and special cis-structure was prepared from a microbial product and added to solution before the sol–gel synthesis reaction. Because of the rapid formation of large and porous aggregates which were 30–50 μm in diameter in suspension without addition of this unique structural surfactant, the prepared ultrafine BaTiO₃ particles caused rapid sedimentation in suspension. The addition of the surfactant in the range of 7.1 wt% for the synthesized BaTiO₃ particles made it possible to decrease the size of the aggregates in suspension as well as the sedimentation velocity while maintaining the stoichiometric composition. The optimum additive content to obtain the minimum aggregate size of about 100–200 nm in diameter and the highest dispersion stability in suspension while maintaining the stoichiometric composition of prepared ultrafine BaTiO₃ particles without other phases was determined at about 7.1 wt%. Because the excess addition of this surfactant at more than 8.5 wt% inhibited the uniform synthesis of BaTiO₃ particles, an amorphous phase with a highly specific surface area and a BaCO₃ phase formed in the synthesized particles.     

Model filled polymers. XV: The effects of chemical interactions and matrix molecular weight on rheology

In order to explore the effects of chemical composition on the rheological behavior o filled polymeric systems, we prepared polystyrene (9PS) and poly(methyl methacrylate) (PMMA) particles crosslinked with either ethylene glycol dimethacrylate (EGDMA) or divinyl benzene (DVB), and mixed these particles in a PMMA matrix. PS particles crosslinked with 10% EGDMA are better dispersed in a PMMA matrix, compared to PS particles, crosslinked with 10% DVB, due to the compatibilizing effect of EGDMA. For PMMA particles crosslinked with DVB, particle-matrix interactions in a PMMA matrix are smaller than in EGDMA-PMMA filled PMMA. Therefore, particles tend to agglomerate in PMMA composites filled with DVB-PMMA particles, especially in a low molecular weight matrix. We compared PMMA matrices of molecular weights 35,000 and 75,000. Higher particle-matrix interaction in the higher molecular weight matrix resulted in lower relative viscosities for DVB-PS filled systems, due to better dispersion of the particles. Composites filled with EGDMA-PS particles behave similarly to those filled with DVB-PS particles. PMMA composites filled with DVB-PMMA particles have a lower relative viscosity in the higher molecular weight PMMA matrix at low shear rates, due to better dispersion in the higher molecular weight matrix. However at high shear rates, particles are well dispersed in both PMMA matrices and, then, the relative viscosity is higher due to better bonding in the higher molecular weight matrix.     

Effects of polyvinylpyrrolidone and carbon nanotubes on magnetorheological properties of iron‐based magnetorheological fluids

Magnetorheological (MR) fluids based on glycol, iron powder, polyvinylpyrrolidone (PVP), and carbon nanotubes (CNTs) were prepared. Effects of polyvinylpyrrolidone and carbon nanotubes on sedimentation stability and magnetorheological properties were studied. It is found that the synergetic effects of PVP and CNTs improve the sedimentation stability significantly, and the addition of CNTs reduces the sedimentation velocity and increases the equilibrium sedimentation ratio of the magnetizable particles in MR fluids remarkably. The addition of PVP can reduce the sedimentation velocity of the magnetizable particles, but cannot increase the equilibrium sedimentation ratio and will not change the up trend of apparent viscosity with the increasing intensity of the external magnetic field. When the PVP content is lower, the increment of original apparent viscosity of the MR fluids at zero‐intensity of magnetic field is inconspicuous, and their values of apparent viscosity under magnetic field are similar. However, the apparent viscosity of the MR fluids increases tremendously when the contents of PVP increase to certain degree. The results show that the synergetic effects of PVP and CNTs not only improve the sedimentation stability of the MR fluid but also promote its magnetorheological effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1653–1657, 2006     

Rheological behavior of low molecular weight polystyrene composites containing monodisperse crosslinked polystyrene beads

Steady shear viscosities and dynamic moduli of polymer composites, consisting of crosslinked polystyrene beads and low molecular weight polystyrene matrix, were measured in a cone-and-plate rheometer at different temperatures. Viscosities and dynamic moduli were found to be very sensitive to filler loading and measurement temperature. Steady shear viscosities of 30% and 40% loaded low molecular polystyrene composites showed a power-law behavior over the entire range of shear rates. Storage and loss moduli were initially linear with frequency on double logarithmic plots, with limiting slopes of 0.3 and 0.1. At high concentration of filler particles, they showed a flat plateau at low frequencies, indicating that these systems exhibit a yield behavior. A 20% PS composite loaded with beads of high crosslink densities resulted in poor dispersion of beads as a result of poor dispersion of particles. PS beads 1.16 μm in diameter showed a higher viscosity. It is due to the apparent increase in loading resulting from broken particles. At low measurement temperature, filler effects were suppressed by high viscosity matrix and showed a similar rheological behavior to high molecular weight by PS matrix. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix.     

Dispersion properties of alumina powders in silica sol

The dispersion of alumina powders in silica sol has been investigated by zeta potential, sedimentation, and rheological measurements. Zeta potential of alumina in silica sol changes significantly in comparison with that of alumina in deionized water. This is caused by the absorption of silica colloidal particles with negative charge on the surface of alumina particles. Sol-dispersed alumina slurry shows a minimum in sedimentation volume and viscosity around pH 10. The viscosity depends strongly on the silica sol concentration and reaches a minimum in 10–15 wt.% silica sols. It is proposed that the dispersion and stabilization of alumina particles in silica sol are attributed to the electrostatic and steric effects of the colloidal particles absorption. Effects of pH, solids content and silica sol concentration on the rheological behavior of sol-dispersed alumina slurries are discussed in detail.     

Solids distribution and rising velocity of buoyant solid particles in a vessel stirred with multiple impellers

The distribution of buoyant solid particles in agitated suspensions has been studied. The investigation was carried out in a baffled vessel characterised by an aspect ratio equal to four and stirred with four radial impellers. Dilute suspensions of single-sized spherical particles of expanded polystyrene (density equal to 90.7 kg/m³) in water were used. Solid concentration was measured with a non-intrusive optical technique. Measurements were performed along the axis of the reactor to obtain steady-state vertical profiles (that increase from the vessel base to the top) as well as at fixed elevations to determine their transient after a pulse of solids injected at the bottom.Both the steady-state profiles and the transient concentration curves were interpreted in terms of the axial dispersion model with sedimentation. By data treatment the rising velocity in the agitated system could be determined, which proved to be significantly smaller than the rising velocity in a still liquid. The ratio of these two velocities is in reasonable agreement with a correlation of the ratio of the settling velocities for heavy particles with the ratio of the Kolmogorov microscale to particle diameter established in the past.     

Large-scale calculation of hydrodynamic transport properties for random suspensions of hard-sphere particles

A numerical method based on fast multipole summation scheme is used to calculate hydrodynamic interactions in random suspensions of non-colloidal hard-sphere particles. The calculation is carried out for suspensions of 1,024 particles randomly placed in periodic unit cell to determine hydrodynamic transport properties such as permeability of a viscous flow through porous medium, effective viscosity of suspension, and sedimentation velocity of the suspended particles. The particle volume fraction ø ranges from 0.01 to 0.25. Effect of particle number N on the transport properties was examined through the numerical calculations with N=64-1,024. It is shown that sedimentation velocity increases with N approaching an estimate for infinite N, and the finite N effect is negligible in effective viscosity and permeability problems. The present scheme is quite useful for obtaining a statistically-averaged quantity for random suspensions. As an example, ensemble-averaged velocity when position of one particle is fixed is numerically obtained in sedimentation problem. The numerical results are shown to be in excellent agreement with theoretical prediction.     

Functional polymers for colloidal applications. I. Structural effects of lipophile-modified polyacrylates on adsorption and dispersion ability

Polyacrylic acids of four molecular weights are prepared. A series of poly(methylacrylate-acrylic acid) copolymers with four specific methylacrylate/acrylic acid ratios and molecular weights has been successfully synthesized from the corresponding polyacrylic acids. These polymers and copolymers are used as dispersants for dispersing TiO₂ into aqueous phase. Viscosity, sedimentation, and electron microscopy are used to evaluate their dispersion ability. The extent of adsorption and the zeta potential are measured to evaluate their adsorption behaviors on the surface of TiO₂. The viscosity, sedimentation, and electron microscopy results are comparable parallel for showing the dispersing ability of a polymer or a copolymer. The polymer (or copolymer), which results in a lower viscosity, shows a slower sedimentation rate and a more homogeneous distribution of particles in microphotographs. The minimum viscosity needed to disperse TiO₂ decreases with the decreasing molecular weight of polyacrylic acid. It was found that partial esterification of polyacrylic acid results in a broader range of minimum viscosity. The trend of the amount adsorbed is similar to that of zeta potential. These two results are used to interpret the viscosity curve.     

乳液聚合法制备核(二氧化钛)-壳(聚苯乙烯)复合粒子

研究了乳液聚合技术用于聚苯乙烯(polystyrene,PS)包覆改性二氧化钛(TiO2)纳米粒子.十二烷基硫酸钠(sodium dodecyl sulfate,SDS)作乳化剂,考察了其浓度对复合粒子形态的影响.用Fourier红外光谱、透射电镜和热重分析表征了无机-有机核-壳复合粒子.用沉降实验评价复合粒子的分散性和分散稳定性.实验表明:SDS浓度为0.8mg/mL时,可以实现PS对纳米TiO2粒子的成功包覆.最佳条件下,乳液聚合单体转化率达62.0%:包覆效率为54.0%;复合粒子中PS占62.6%;复合粒子平均粒径为181nm.复合粒子能在乙酸乙酯中形成均匀分散体系.     

Liquid Radial Dispersion in Liquid-solid Circulating Fluidized Beds with Viscous Liquid Medium

Liquid dispersion in the radial direction was investigated in the riser of a viscous liquid-solid fluidized bed 0.102 m in diameter and 3.5 m in height. Pressure fluctuations in the riser were also measured and analyzed to examine the behavior of fluidized particles. Effects of liquid velocity (0.15-0.45 m/s), solid circulation rate (2-8 kg/m²s), particle size (1-3 mm), and liquid viscosity (0.96-38 mPas) on pressure fluctuations and the liquid radial dispersion coefficient were determined. The infinite space model was employed to obtain the radial dispersion coefficient from the radial concentration profiles of the tracer. The pressure fluctuations were analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency obtained from the autocorrelation coefficient or power spectral density function of pressure fluctuations decreases with increasing liquid viscosity or liquid velocity, but it increases with increasing particle size. The liquid radial dispersion coefficient decreases with increasing liquid velocity or viscosity, but it increases as the solid circulation rate or particle size increases. The liquid radial dispersion coefficient is related closely to the resultant behavior of fluidized particles. The radial dispersion coefficient has been well correlated with operating variables in terms of dimensionless groups.     

Liquid Radial Dispersion in Liquid-solid Circulating Fluidized Beds with Viscous Liquid Medium

Liquid dispersion in the radial direction was investigated in the riser of a viscous liquid-solid fluidized bed 0.102 m in diameter and 3.5 m in height. Pressure fluctuations in the riser were also measured and analyzed to examine the behavior of fluidized particles. Effects of liquid velocity (0.15–0.45 m/s), solid circulation rate (2–8 kg/m²s), particle size (1–3 mm), and liquid viscosity (0.96–38 mPas) on pressure fluctuations and the liquid radial dispersion coefficient were determined. The infinite space model was employed to obtain the radial dispersion coefficient from the radial concentration profiles of the tracer. The pressure fluctuations were analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency obtained from the autocorrelation coefficient or power spectral density function of pressure fluctuations decreases with increasing liquid viscosity or liquid velocity, but it increases with increasing particle size. The liquid radial dispersion coefficient decreases with increasing liquid velocity or viscosity, but it increases as the solid circulation rate or particle size increases. The liquid radial dispersion coefficient is related closely to the resultant behavior of fluidized particles. The radial dispersion coefficient has been well correlated with operating variables in terms of dimensionless groups.     

Effect of dispersion states (electrostatic/electrosteric stabilization) on particles arrangement in the yttria-stabilized zirconia sediments

In the present work, particle arrangement and their packing in the sediment layer of zirconia suspension were studied. To evaluate the particle settling, aqueous suspensions of zirconia nanoparticles were prepared in different dispersion states. In one state, Dolapix CE64 was used as a dispersant to provide electrosteric mechanism. In another state, pH of the suspension was adjusted at 4 to provide electrostatic mechanism. The other state was the combination of dispersant and pH adjustment which resulted in the most stable suspension. First of all, the stability of all dispersion states was evaluated by zeta potential, sediment volume (SV) and height, viscosity, and packing density (PD). Then, the sediment layers of all suspensions were characterized. Incorporation of electrostatic mechanism was resulted in a main decrease in viscosity with high surface charges, while electrosteric mechanism caused lower sedimentation of particles. Fall velocities of particles/agglomerates were estimated, and the influences of dispersion states on the particles fall velocities were characterized. The microstructural observation revealed homogeneous packing of particles in the sediment layer of the stable suspension demonstrating the proper dispersion of particles. Dolapix CE64 and pH adjustment resulted in a uniform arrangement of particles without agglomeration and spherical and regular granules with a uniform shape.     

Aggregate structures formed via a bridging flocculation mechanism

A high molecular weight cationic polyelectrolyte has been used to flocculate a colloidal dispersion of anionic polystyrene latex particles. The polymer used had a high charge density and the flocculation occurred at a solution pH where both the polymer and the particles were fully charged. Under these conditions, flocculation is expected to occur through a bridging flocculation mechanism. Low angle laser light scattering has been used to follow the flocculation process as a function of time; parameters of interest were the aggregate sizes, size distributions, and aggregate mass fractal dimensions. The light scattering measurements showed that the flocs formed had a mass fractal character. All the systems examined here were overdosed with respect to the optimum flocculation concentration of polymer. Under these conditions, decreasing the polymer concentration was seen to result in an increased flocculation efficiency. A secondary growth process was also observed whereby initially formed fractal aggregates can subsequently aggregate again. These larger aggregates are also expected to be mass fractals although this cannot be determined from the light scattering measurements due to the superposition of Fraunhofer diffraction effects. This type of fractal-in-fractal character is unusual.     

Effect of viscosity of shell solution on the content of solid powder as core material in microencapsulation by the drying‐in‐liquid method

Solid powder generating minus ion was microencapsulated by polystyrene with the drying‐in‐liquid method. In the microencapsulation, (R)‐(+) limonene as the solvent for polystyrene and ethylene glycol as the continuous phase were adopted instead of the conventional organic solvent such as dichloromethane, benzene and toluene, and water, respectively. It was mainly investigated whether the solvents adopted here could be applied to the drying‐in‐liquid method or not and how the viscosity of the shell solution and the oil soluble surfactant affected the content of core material. The oil soluble surfactant made hydrophilic solid powder more hydrophobic and resulted in an increase of the content. Microcapsules containing solid powder could be prepared with the drying‐in‐liquid method using (R)‐(+) limonene and ethylene glycol. An increase in the viscosity of the shell solution repressed the movement of solid powder particles in a droplet of the shell solution during the microencapsulation process and resulted in the higher content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

pH值对包覆改性SiC料浆分散特性和流变性的影响

通过zeta电位、沉降实验、流变特性、粘度等测试表征pH值对包覆改性SiC料浆分散特性和流变性的影响。研究表明:以偶联剂作为基础层,有机聚电解质作为分散功能层的有机包覆改性SiC粉体主要通过静电空间位阻效应实现稳定分散,调节pH值可以控制接枝聚合物水解产物的解离方式,从而改变了颗粒表面的电荷种类和电荷密度,包覆改性粉体的流动特性也发生变化。调整料浆pH值约11可制备出固相体积分数达56％、表观粘度为568 MPa·s的稳定料浆。     

Particle fluctuations and dispersion in three-phase fluidized beds with viscous and low surface tension media

Particle fluctuations and dispersion were investigated in a three-phase (gas–liquid–solid) fluidized bed with an inside diameter of 0.102 m and height of 2.5 m. Effects of gas and liquid velocities, particle size (0.5–3.0 mm), viscosity (1.0–38×10⁻³ Pa s) and surface tension (52–72×10⁻³ N/m) of continuous liquid media on the fluctuating frequency and dispersion coefficient of fluidized particles were examined, by adopting the relaxation method base on the stochastic model. The fluctuations and dispersion of fluidized solid particles were successfully analyzed by means of the pressure drop variation with time, which was chosen as a state variable, based on the stochastic model. The fluctuating frequency and dispersion coefficient of particles increased with increasing gas velocity, due to the increase of bubbling phenomena and bed porosity in which particles could move, fluctuate and travel. The frequency and dispersion coefficient of particles showed local maximum values with a variation of liquid velocity. The two values of fluctuating frequency and dispersion coefficient of particles increased with increase in particle size, but decreased with increase in liquid viscosity due to the restricted movement and motion of particles in the viscous liquid medium. Both fluctuating frequency and dispersion coefficient of particles increased with decrease in surface tension of liquid phase, due to the increase of bubbling phenomena with decrease in σ_L. The values of obtained particle dispersion coefficient were well correlated in terms of dimensionless groups as well as operating variables.     

Rheology and sedimentation velocity of alkaline suspensions of hematite particles at elevated temperature

This study aims to characterize the sedimentation velocity and the rheology of suspensions of hematite particles suspended in strongly alkaline media at 100 and 110 °C, as done for an alternative electrochemical process in development for iron production by direct electrode reduction of hematite. Considering the medium used in the process, i.e. 12% (v/v) suspension of hematite particles in 50% sodium hydroxide aqueous, the sedimentation velocity of hematite particle at 110 °C is 0.010 mm/s, which is very slow because the average size of the solid particles is around 10 μm and the significant collisions and interactions occuring between the particles in the concentrated suspension. Two geometries were used to characterize the rheological behavior of the apparent viscosity of the suspension of 12% (v/v) (i.e. 33 wt%) at 100 °C: a conventional Couette geometry and a helical ribbon mixer. The suspension was found shear thinning in the range of shear rate studied. The rheological behavior of the suspension can be described by a power-law model. The apparent viscosity of the hematite suspension estimated at a shear rate between 0.5 and 10 s⁻¹ is between 100 and 20 mPa s for the two geometries. The apparent viscosity calculated from the terminal velocity of 10 μm particles is of the same order of magnitude of the results obtained with the two rheometer configurations. The effect of the particle concentration on the sedimentation velocity and viscosity of the hematite suspensions was also studied.