Sedimentation of large colloidal particles through semidilute polymer solutions

The sedimentation of various spherical particles with radii 25–175 Å in poly(ethylene oxide) aqueous polymer solutions have been investigated by analytical ultracentrifugation. As already observed by Laurent and Pietruszkiewicz (Biochim. Biophys. Acta 1961, 49, 258) the decrease in the sedimentation rate with polymer concentration, c, and particle radius, R, is of the form S ∝ exp(?Ac^y). Present experiments in semidilute solutions show that: (1) A is proportional to R but independent of polymer molecular weight; (2) y is $\text{? 0.62}$, significantly higher than the value of 0.5 claimed by previous authors; (3) polymer adsorption onto the particle surfaces has to be taken into account. Our results are in reasonable agreement with a simple form $\text{S ∝}\text{exp}\text{(}\text{?R}\text{ξ}\text{)}$ where ξ is the correlation length ∝_c^?v with v ?0.75. The semidilute polymer solution can thus be viewed as a statistical network of mesh ξ, the retardation factor being governed by the elastic distortion of the network due to the moving particles.     

A population balance model for flocculation of colloidal suspensions by polymer bridging

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously.     

Characterization and modeling of sintering of polymer particles

An experimental study of simultaneous sintering of several particles has been carried out using spherical polymer grains. Considering rotational molding condition, coalescence of several grains in contact, happens simultaneously on internal surface of the mould. Theoretical model based on the effect of surface tension and viscosity can accurately predict the coalescence of a pairs of grains. However, it was observed in this study that coalescence rate changes with presence of neighboring grains and their position and the theoretical model proposed for two grains, is not able to predict the coalescence rate of mutli‐grains. Based on this finding, we have modified this model with taking into account the effect of neighboring particles in the sintering rate of multi‐grains. Obtained modified model is capable of predicting the multi‐grains sintering rate observed in this study. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structures and interactions between two colloidal particles in adsorptive polymer solutions

The role of weak adsorptive polymer chains in the colloidal particles solution is studied by self-consistent field theory (SCFT). The numerical results show the potential between colloids are attractive interaction. Besides the depletion effects the chain conformations such as loop, tail and bridge between two spherical colloidal particles play important roles. The quantitative polymer concentration dependent chain conformations and then the effective potential are also addressed.     

Characterization of crosslinked,macroporous, monosized polymer particles

Macroporous, monosized poly(meta‐divinylbenzene) and poly(para‐divinylbenzene) beads have been prepared by the two‐step activated swelling method with toluene or 2‐ethylhexanoic acid as pore‐forming agents. The type of divinylbenzene isomer as well as the type of porogen has a large effect on both physical and chemical properties of the monodisperse beads. Large pores are obtained with 2‐ethylhexanoic acid as porogen while beads prepared in the presence of toluene consist of only small pores and exhibit a shrinking behavior upon drying. The beads have considerable amounts of residual vinyl groups at the end of polymerization, as determined by bromination and Fourier transform IR analysis. The morphology and texture of the particles have been investigated by scanning electron microscopy and atomic force microscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 152–169, 2000     

Redispersible dried hydroxyapatite particles with grafted pH-sensitivity polymer brushes of poly(styrene-co-4-vinylpyridine)

Reversible aggregation-redispersion transition of colloidal particles is of considerable importance in colloidal science and various industrial fields. In the present study, stimuli-responsive hybrid hydroxyapatite (HA) particles were prepared with redispersible ability in aqueous solutions even after separation from the “as synthesized” state and subsequent dry heat treatment. We firstly modified HA particles with sodium oleate as chelating agent, then introduced bromoalkyl functional groups through an addition reaction of unsaturated oleate molecule with bromine, and finally grafted polymer brushes of polystyrene-co-4-vinylpyridine onto HA. It was the pH-sensitive polymer shell that had rendered HA particles the redispersible ability, which was attributed to the protonation of the pyridine blocks in acidic solutions. The reversible dispersion-aggregation transition of HA could be controlled by alternating the pH value of aqueous solution. Protonated pyridine blocks had provided enough electrostatic and steric repulsions for colloidal HA to avoid effective collision.     

Polyaniline prepared in solutions of phosphoric acid: Powders, thin films, and colloidal dispersions

Polyaniline (PANI) has been prepared by the oxidation of aniline with ammonium peroxydisulfate in the 0-4 M phosphoric acid. The maximum conductivity of PANI, 15.5 S cm⁻¹, was found with PANI prepared in the presence of 1 M phosphoric acid. The mass loss after deprotonation with ammonium hydroxide revealed that relatively large amounts of phosphoric acid were associated with PANI if the polymerization had been carried out at higher acid concentration. This suggests the protonation of both the imine and amine nitrogens in PANI, the increased adsorption of phosphoric acid by PANI, or the presence of polyphosphate counter-ions. The increasing content of phosphoric acid is also reflected in the increase of sample density. FTIR spectra of ammonium salts collected after deprotonation proved that the counter-ions of the sulfate type, resulting from the decomposition of peroxydisulfate, always participated in the protonation of PANI. The proportion of sulfate to phosphate counter-ions was reduced as the concentration of phosphoric acid in the medium increased.Thin PANI films were produced in situ on glass surfaces immersed in the reaction mixture during the polymerization of aniline. Optical absorption has been used to assess their thickness, 70-140 nm, which was found to be virtually independent of the acid concentration. The film conductivity was comparable with the conductivity of the PANI powders produced at the same time. Colloidal dispersions were obtained when the reaction mixture contained poly(N-vinylpyrrolidone). The particle size, 200-260 nm, and polydispersity, determined by dynamic light scattering, were virtually independent of the concentration of phosphoric acid. The films produced on glass during the dispersion polymerization of aniline were thinner, 20-90 nm, compared with those grown in the precipitation polymerization.     

Investigation of aggregation, breakage and restructuring kinetics of colloidal dispersions in turbulent flows by population balance modeling and static light scattering

Quantitative modeling of aggregating colloidal systems is the underlying problem in many industrial processes, such as micro and nanoparticle processing, crystallization or flocculation. Population balance models with various aggregation and breakage kernels have been proposed in order to describe aggregating systems, but they have been rarely validated against appropriate experimental data. Typically, model parameters are fitted against a single measured moment of the cluster distribution which can usually be equivalently described using several variations of the set of parameters underlying the relevant aggregation, breakage and restructuring kernels. In order to discriminate among alternative models we propose an approach based on measurement and quantitative modeling of multiple moments of the cluster mass distribution, such as those obtained from static light scattering measurements. This approach is applied to aggregation processes in turbulent conditions in order to test alternative kernels for aggregation, breakage, and restructuring kinetics. We present a detailed study on the sensitivity of measurables from static light scattering with respect to commonly used aggregation and breakage kinetic models. In particular, we analyze the dynamic and steady state behavior of two measurables: the average radius of gyration and the average zero angle intensity which represent two independent moments of the cluster mass distribution. In addition, we discuss the effect of cluster structure and mass distribution on the average structure factor and the apparent fractal dimension measured by static light scattering, in order to assess what structural information can be reliably extracted from such measurements.     

Enzymatic synthesis of colloidal polyaniline particles

Polyaniline colloidal particles were enzymatically synthesized in aqueous media using poly(vinyl alcohol) as steric stabilizer. Hydrochloric acid, toluenesulfonic acid, and camphorsulfonic acid were used as doping agents during polymerization. Polyaniline showed chemical redox reversibility as demonstrated by changes in its electronic absorption spectra. Fourier transform infrared and UV-visible spectroscopic studies indicate a linear chemical structure of the synthesized polymer, whereas the results from X-ray photoelectron spectroscopy indicate the adsorption of poly(vinyl alcohol) at the surface of the particles. The doping agent used during the enzymatic polymerization of aniline influenced morphology and thermal stability of the synthesized particles. Polyaniline colloids prepared using p-toluenesulfonic acid showed spherical morphology and a narrow size distribution as shown by scanning electron microscopy and dynamic light scattering.     

Size-dependent mechanical behavior of nanoscale polymer particles through coarse-grained molecular dynamics simulation

Anisotropic conductive adhesives (ACAs) are promising materials used for producing ultra-thin liquid-crystal displays. Because the mechanical response of polymer particles can have a significant impact in the performance of ACAs, understanding of this apparent size effect is of fundamental importance in the electronics industry. The objective of this research is to use a coarse-grained molecular dynamics model to verify and gain physical insight into the observed size dependence effect in polymer particles. In agreement with experimental studies, the results of this study clearly indicate that there is a strong size effect in spherical polymer particles with diameters approaching the nanometer length scale. The results of the simulations also clearly indicate that the source for the increases in modulus is the increase in relative surface energy for decreasing particle sizes. Finally, the actual contact conditions at the surface of the polymer nanoparticles are shown to be similar to those predicted using Hertz and perfectly plastic contact theory. As ACA thicknesses are reduced in response to reductions in polymer particle size, it is expected that the overall compressive stiffness of the ACA will increase, thus influencing the manufacturing process.     

Trickle bed reactor diluted with fine particles and coiled tubular flow-type reactor for kinetic measurements without external effects

Gas and liquid velocities in laboratory scale trickle bed reactors are one or two orders of magnitude lower than those in commercial reactors. Then, the kinetic data may include the external effects. This shortcoming of laboratory scale trickle bed reactor can be resolved by diluting the catalyst bed with fine inert particles. The catalyst bed dilution increases dynamic liquid holdup, pressure drop, gas–liquid mass transfer coefficient. Hydrogenation of 2-phenylpropene on Pd/Al₂O₃ was performed with the trickle bed reactor diluted with fine inert particles and the coiled tubular flow-type reactor to compare the kinetics with that of the basket type batch reactor. The trickle bed reactor diluted with fine inert particles is suitable to obtain the reaction rate without external effects even if the liquid velocity is low. The coiled tubular flow-type reactor should be used at high gas velocities.     

Characterization of air plasma‐treated polymer surfaces by ESCA and contact angle measurements for optimization of surface stability and cell growth

A radiofrequency air plasma has been used to incorporate new functionalities at the surface of cycloolefin polymers (Zeonex® and Topas®), polymethyl methacrylate (PMMA), styrene–acrylonitrile copolymer (SAN), and polystyrene (PS). The main goals with the plasma treatment of the different plastics were to hydrophilize the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios (50 to 100 W/sccm) became highly hydrophilic (water contact angles of about 5 degrees) and stable towards washing in 70% (v/v) ethanol. Those treated at lower power/gas flow ratios (3 to 10 W/sccm) were less hydrophilic and not wash‐stable. Cell growth properties of HeLa cervix carcinoma cells as good as on commercial tissue‐culture polystyrene could be obtained for Zeonex, SAN, and PS, treated at relatively low RF power/gas flow ratios. However, no untreated plastics were suitable for culturing these cells. XPS spectra features show that ester, ether/alcohol, and ester/carboxyl groups are formed during the plasma treatments of the different plastics. Measurable amounts of carboxylic acid carbon after plasma treatment were only observed for PS and Topas. Furthermore, at high RF power/gas flow ratios fluorine, aluminium and silicon were incorporated in all investigated plastics surfaces due to ablation–deposition processes in the reaction chamber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2618–2625, 2002     

Modification of thermosetting resins and composites through preformed polymer particles: A review

A review is presented that focuses on preformed particle modification of high performance thermosetting resins and composite systems. The modifiers reviewed consist of thermoplastic and rubber preformed particles with no size limitations. Both organic and inorganic preformed polymer particles are considered but not glass or hollow spheres. In this text, preformed particles are defined as those which do not require phase separation and remain in the shape in which they were added to the neat resin or composite. Therefore, these particles may be developed prior to the resin formulation and then added to the thermosetting resin or developed in situ (during resin formulation) before the resin is catalyzed or cured. This technical review of preformed particle modification of thermosetting resins and composite systems summarizes the utilization of these materials and their performance.     

具有核壳结构的聚合物粒子

概述了具有核壳结构的聚合物粒子的制备方法、形成条件及形成机理,介绍了它们在作为高分子材料的抗冲击改性剂和增韧剂、涂料和粘合剂等领域的应用,并对这一领域的发展进行了展望。     

A modified Richardson-Zaki equation for fluidization of Geldart B magnetic particles

Gas bubbles are suppressed in fluidized beds of Geldart B magnetic particles when a homogenous magnetic field is applied due to the formation of straight-chain aggregates. Expansion of the non-bubbling bed depends on the orientation of the applied field with respect to gas flow. Hindered bed expansion is reported for axial fields, whereas enhanced expansion is observed for transversal fields. In the present paper we propose a modified Richardson-Zaki equation that takes into account aggregation and chain orientation to describe bed expansion as the gas flow is increased. The only free parameter in this equation is the chain length, that is directly related to the field intensity through a magnetic granular Bond number, defined as the ratio of magnetic to gravitational energy per unit volume. Results from the proposed model are successfully compared with published data in the literature.     

Coagulation of colloidal particles in water by chitosan

The feasibility of applying chitosan, as prepared from the crab chitin, was assessed in this study for the coagulation of colloidal particles. A series of batch flocculation tests with chitosan under different conditions was also conducted. The results indicate that chitosan is a potent coagulant for bentonite suspension. The relationship between the optimum chitosan dosage and the turbidity of the bentonite suspension is presented as a linear correlation. The evidence infers that an adequate range of the coagulant dosage is the primary consideration in determining the removal efficiency for the turbidity of the source water. It also indicates that the coagulation behavior for kaolinite by chitosan is different from that of bentonite, i.e., chitosan fails to form a good aggregate with kaolinite. Turbid water containing particles which show behavior similar to kaolinite apparently need to have some bentonite particles added as coagulant aid, thereby improving the aggregation of the colloid particles with chitosan. Moreover, the effect of pH on the coagulation efficiency of chitosan is insignificant. The evidence infers that charge neutralization is not a major mechanism controlling the formation of floc for chitosan coagulation.     

Electrophoresis of colloidal particles in a salt-free medium

A general theory for the electrophoretic mobility of dilute spherical colloidal particles in a salt-free medium containing counterions only is given. This theory assumes that each particle is surrounded by a spherical free volume, within which electroneutrality as a whole holds. It is shown that the mobility can be obtained from the balance between the Stokes drag for the case where the particle is uncharged and the pressure due to the excess counterion charge on the outer boundary of the free volume. The mobility μ is thus expressed as μ=Qexp(y(R))/D, where Q is the particle surface charge, D is the drag coefficient of the particle when uncharged, and y(R) is the scaled potential value at the outer boundary of the free volume.     

Synthesis of silver/polymer colloidal composites from surface-functional porous polymer microspheres

This study presents a different colloidal silver (Ag)/polymer system where Ag nanoparticles are deposited uniformly onto surface-functional porous poly(ethylene glycol dimethacrylate-co-acrylonitrile) (poly(EGDMA-co-AN)) microspheres. The formation and morphology of the composite microspheres were characterized from electron microscopy and X-ray diffraction analyses. The significance of the present report is that owing to the high affinity between Ag and nitrile group (CN) on the large surface of the microspheres, the Ag nanoparticles having a face-centered cubic phase were incorporated evenly into the deep pores of the microspheres with fine size and size distribution. In the preservation test, the Ag/poly(EGDMA-co-AN) composite microspheres obtained showed an excellent anti-bacterial performance, elucidating a high applicability for a new preservative.