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PubMed1999

Reactions of a Trifunctional Silane Coupling Agent in the Presence of Colloidal Silica Sols in Polar Media.

Reactions of 3-glycidoxypropyltrimethoxysilane (GPS) in a water-rich environment with silica colloids were studied. (29)Si NMR spectroscopy was used to monitor quantitatively the variation in GPS hydrolysis, condensation, and adsorption with pH and water concentration. The results show the competition between adsorption on the silica surface and condensation polymerization of GPS in the bulk liquid and are used to identify conditions favorable to surface modification. The presence of colloidal silica was shown to increase the apparent GPS dimerization rate, suggesting either surface catalysis or an increased local reactant concentration in the electrical double layer around the silica colloids. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Hydrodynamic and Colloidal Interactions in Concentrated Charge-Stabilized Polymer Dispersions.

Hydrodynamic and colloidal interactions are explored in concentrated, charge-stabilized colloidal dispersions by measuring the dependence of rheology (e.g., low and high-shear viscosity, high-frequency viscosity, and modulus) and self-diffusivity on salt content, particle size, and concentration. Model, sulfonated polystyrene lactices of varying diameter are prepared and investigated by shear rheology, high-frequency torsional resonance, electrophoresis, titration, and dynamic light scattering. The high-frequency and high-shear viscosity both are dominated by hydrodynamic interactions, but are shown not to be identical, due to the microstructure distortion resulting from high shear rates. The short-time self-diffusion is also shown to be insensitive to direct particle interactions, but has a different concentration dependence than the high-frequency viscosity, further illustrating a predicted violation of a generalized Stokes-Einstein relationship for these properties. The apparent colloidal surface charge is extracted from the high-frequency elastic modulus measurements on concentrated dispersions. The surface charge is in good agreement with results from critical coagulation concentration measurements and perturbation theories, but disagrees with electrophoretic mobility experiments. This indicates that the effective surface charge determined by torsional high-frequency measurements is a more reliable predicter of the salt stability of charge-stabilized dispersions, in comparison to zeta-potentials determined from electrophoretic mobilities. Further, we demonstrate by direct comparison that measurements of the apparent plateau modulus by rotational rheometry underestimate the true, high-frequency modulus and provide unreliable estimates for the surface charge. Copyright 2000 Academic Press.

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PubMed2000

Effect of a Dynamic Stern Layer on the Sedimentation Velocity and Potential in a Dilute Suspension of Colloidal Particles.

In this paper the theory of the sedimentation velocity and potential (gradient) in a dilute suspension of charged spherical colloidal particles developed by Ohshima et al. (H. Ohshima, T. W. Healy, L. R. White, and R. W. O'Brien, J. Chem. Soc., Faraday Trans. 2, 80, 1299 (1984)) has been modified to include the presence of a dynamic Stern layer on the particle surfaces. The starting point has been the theory that Mangelsdorf and White (C. S. Mangelsdorf, and L. R. White, J. Chem. Soc., Faraday Trans. 86, 2859 (1990)) developed to calculate the electrophoretic mobility of a colloidal particle allowing for the lateral motion of ions in the inner region of the double layer (dynamic Stern layer). The effects of varying the different Stern layer parameters on the sedimentation velocity and potential are discussed and compared to the case when a Stern layer is absent. The influence of electrolyte concentration and zeta potential of the particles is also analyzed. The results show that regardless of the chosen set of Stern layer and solution parameters, the presence of a dynamic Stern layer causes the sedimentation velocity to increase and the sedimentation potential to decrease, in comparison with the standard case (no Stern layer present). These changes are almost negligible when sedimentation velocity is concerned, but they are very important when it comes to the sedimentation potential. A justification for this fact can be given in terms of an Onsager reciprocal relation, connecting the magnitudes of the sedimentation potential and the electrophoretic mobility. As previously reported, the presence of a dynamic Stern layer exerts a great influence on the electrophoretic mobility of a colloidal particle, and by means of the Onsager relation, the same is confirmed to occur when the sedimentation potential is concerned. Copyright 2000 Academic Press.

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PubMed2000

Properties of Poly(N-isopropylacrylamide)-Grafted Colloidal Silica.

Poly(N-isopropylacrylamide-co-3-trimethoxysilylpropyl methacrylate) was prepared by radical polymerization and was grafted onto the surface of spherical colloidal silica. The copolymer, which had on average 1 silyl group per chain, condensed on the silica dispersed in THF at 60 degrees C. The resulting particles had a critical coagulation concentration of calcium chloride of 500 mM at room temperature, indicating robust colloidal stability. By contrast, heating the suspension to 50 degrees C lowered the critical coagulation concentration by more than three orders of magnitude, giving a value of 0.1 mM. Thus, the PNIPAM shell induced temperature-sensitive colloidal stability in the silica dispersion. The coated silica particles were also surface active. However, the surface tension of 50 mJ/m(2) at 25 degrees C is 15% higher than the corresponding value for PNIPAM solutions. Copyright 2000 Academic Press.

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PubMed2000

Morphology and Luminescence of(GdY)(2)O(3):Eu Particles Prepared by Colloidal Seed-Assisted Spray Pyrolysis.

(Gd(x)Y(1-x))(2)O(3):Eu [x=0, 0.25, 0.5, 0.75, 1.0] phosphor particles with 6 at.% Eu dopant of total concentration were prepared using spray pyrolysis. The effects of composition on the morphology, crystallinity, and photoluminescence characteristics of composite particles were investigated. The morphological control of (Gd(x)Y(1-x))(2)O(3):Eu particles in spray pyrolysis was also attempted by using colloidal and aqueous solutions. The particles prepared from colloidal solutions containing small amounts of Gd or Y hydroxy carbonate sol as seed material had spherical and filled morphology after the post-treatment at high temperature. On the other hand, the (Gd(x)Y(1-x))(2)O(3):Eu particles prepared from aqueous solutions were hollow and porous after post-treatment in all compositions. Particles prepared from colloidal solutions had photoluminescence emission intensities higher than those of particles prepared from aqueous solutions. Copyright 2000 Academic Press.

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PubMed2000

Low Reynolds Number Interactions between Colloidal Particles near the Entrance to a Cylindrical Pore.

The interaction between stable colloidal particles arriving at a pore entrance was studied using a numerical method for the case where the particle size is smaller than but of the same order as the pore size. The numerical method was adapted from a front-tracking technique developed for studying incompressible, multifluid flow by S. O. Unverdi and G. Tryggvason (J. Comp. Phys. 100, 25, 1992). The method is based on the finite difference solution of Navier-Stokes equation on a stationary, structured, Cartesian grid and the explicit representation of the particle-liquid interface using an unstructured grid that moves through the stationary grid. The simulations are in two dimensions, considering both deformable and nondeformable particles, and include interparticle colloidal interactions. The interparticle and particle-pore hydrodynamic interactions, which are very difficult to determine using existing analytical and semi-numerical, semi-analytical techniques in microhydrodynamics, are naturally accounted for in our numerical method and need not be explicity determined. Two- and three-particle motion toward a pore has been considered in our simulations. The simulations demonstrate how the competition between hydrodynamic forces and colloidal forces acting on particles dictate their flow behavior near the pore entrance. The predicted dependence of the particle flow behavior on the flow velocity and the ratio of pore size to particle size are qualitatively consistent with the experimental observations of V. Ramachandran and H. S. Fogler (J. Fluid Mech. 385, 129, 1999). Copyright 2000 Academic Press.

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PubMed2000

Coupled Influence of Colloidal and Hydrodynamic Interactions on the RSA Dynamic Blocking Function for Particle Deposition onto Packed Spherical Collectors.

The influence of electrostatic double-layer and hydrodynamic interactions on random sequential adsorption (RSA) of colloidal particles onto packed spherical collectors was investigated using inverse analysis of colloid breakthrough data obtained from well-controlled particle deposition experiments. Deposition experiments were carried out using monodisperse aqueous suspensions of positively charged latex colloids and packed columns of negatively charged uniform glass beads for different combinations of ionic strength, particle size, and approach velocity. From the experimental particle breakthrough data, the initial particle deposition rates and the virial coefficients of the dynamic blocking function based on RSA mechanics were determined. The magnitudes of the virial coefficients were observed to increase from the hard sphere values with increasing flow rates and decreasing ionic strengths of the background electrolyte. Particle size also plays a significant role in governing the deposition dynamics. The deviation from the hard sphere RSA behavior becomes more prominent for larger particles. Copyright 2000 Academic Press.

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PubMed2000

Soft X-Ray Spectromicroscopy Investigation of the Interaction of Aquatic Humic Acid and Clay Colloids.

Soft X-ray spectromicroscopy investigations of the interaction of aquatic humic acid (HA) and montmorillonite colloids have been performed in situ at the NSLS X1-A STXM endstation. Images have been recorded of montmorillonite particles, HA aggregates, and mixed suspensions of both montmorillonite + HA and montmorillonite + carboxyl polystyrene microspheres, as reference organic colloids. Special emphasis has been placed on the sample preparation technique in order to keep the colloid particles hydrated during all measurements. C 1s near edge absorption fine structure extracted from STXM image stacks reveals electronic transitions corresponding to functional -COOH and -C(6)H(5) groups present in HA and polystyrene. XANES peak intensities reflect the relative amounts of these two carbon functional groups in the organic particles. For example, the greater amount of carboxyl groups in HA compared to the latex reference particles affects a larger 1s-->pi* transition intensity. A specific form of montmorillonite-HA particle agglomeration at near-neutral pH has been observed. Under these conditions, we found no separate clustering of HA. Instead, STXM images show the HA to coat the clay mineral surface, leading to nearly a fractal manner of aggregation. Copyright 2000 Academic Press.

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PubMed2001

Linearity in Optical Absorption Spectra and Gold-Silver Alloy Colloidal Particles in Epoxy Resin.

Gold-silver alloy colloids were produced in epoxy resin by thermal decomposition of gold and silver complexes, and their optical absorption spectra were measured. A linear law was found for the maximal absorption wavelengths: the maximal absorption wavelength for gold-silver alloy colloids of arbitrary composition was determined from the wavelengths for pure gold and pure silver colloids and the initial concentration ratio of gold and silver complexes. The change of absorbance and absorption wavelengths with heating periods is presented. Copyright 2001 Academic Press.

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PubMed2002

Investigation of particle interactions in concentrated colloidal suspensions using frequency domain photon migration: monodisperse systems.

Frequency domain photon migration (FDPM) measurements were conducted to assess particle interactions of concentrated, monodisperse, polystyrene samples obtained directly from industry by using multiple scattering light. The angle-integrated static structure factor, S(q), and static structure factor at small wave vector q, S(0), were obtained from FDPM measurements at high volume fractions ranging from 0.05 to 0.3, and were compared with those obtained from the monodisperse hard sphere Percus-Yevick (HSPY) model. Effects of different colloid sizes on structure factor evaluated at two different wavelengths were also investigated. Results show that the monodisperse HSPY model is suitable for accounting for particle interactions and local microstructures in these colloidal suspensions. Upon using the HSPY model, particle sizes of polystyrene suspensions were recovered from FDPM measurements at high volume fractions (up to 0.3), which agree well with the DLS measurement of diluted sample ( approximately 0.001). The study of polydispersity effect shows that the FDPM method can be successfully used for recovering the mean particle size of polydisperse colloidal suspension with low polydispersity (<16%) under the assumption of monodisperse hard sphere systems.

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PubMed2002

Direct surface force measurement in water using a nanosize colloidal probe technique.

The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true nano size (<10 nm), surface forces are increasingly important. Nanoparticles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. The current tools for directly measuring interaction forces such as a surface force apparatus or atomic force microscopy (AFM) are limited to particles much larger than nanosize. Here a modified colloidal probe technique is suggested using a multiwalled carbon nanotube (MWNT) to overcome this problem. Determination of zero separation in AFM is critical to extract a reliable force-separation curve when MWNT is used as a probe. Hence, a systematic approach to the data collection for a nanosize colloidal probe is proposed and a sample of a direct surface force measurement curve obtained with the MWNT probe is presented.

Letter↗

PubMed2002

Partitioning of clay colloids at air-water interfaces.

Colloid sorption onto air-water interfaces in a variety of natural environments has been previously recognized, but better quantification and understanding is still needed. Affinities of clay colloids for the air-water interface were measured using a bubble-column method and reported as partition coefficients (K). Four types of dilute clay suspensions were measured in NaCl solutions under varying pH and ionic strength conditions: kaolinite KGa-1, illite IMt-2, montmorillonite SWy-2, and bentonite. The K values of three types of polystyrene latex particles with different surface-charge properties were also measured for comparison. Kaolinite exhibited extremely high affinity to the air-water interface at pH values below 7. Illite has lower affinity to air-water interfaces than kaolinite, but has similar pH dependence. Na-montmorillonite and bentonite clay were found excluded from the air-water interface at any given pH and ionic strength. Positively and negatively charged latex particles exhibited sorption and exclusion, respectively, at the air-water interface. These results show the importance of electrostatic interactions between the air-water interface and colloids, especially the influence of pH-dependent edge charges, and influence of particle shape.

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PubMed2002

Reduction of colloidal manganese dioxide by manganese(II).

The reduction of colloidal MnO(2) by Mn(2+) in aqueous HClO(4) has been studied by a spectrophotometric method. The reaction product is Mn(III). The reaction is of first order in both colloidal MnO(2) and H(+), whereas it presents a fractional order (0.58+/-0.02) in Mn(2+). The reaction is retarded by addition of NaClO(4), but is not affected by addition of tert-butanol. The corresponding activation energy is 29.5+/-1.3 kJ mol(-1). The reaction is catalyzed by Na(4)P(2)O(7), and the pyrophosphate-catalyzed reaction is of first order in both colloidal MnO(2) and pyrophosphate and of fractional order (0.64+/-0.01) in Mn(2+), whereas its rate presents a complex dependence on the concentration of H(+). The pyrophosphate-catalyzed reaction is accelerated by addition of both NaClO(4) and tert-butanol. The corresponding activation energy is 49.7+/-3.0 kJ mol(-1). Mechanisms in agreement with the experimental data are proposed for both the parent and the pyrophosphate-catalyzed reactions.

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PubMed2002

A comparative study on photo-induced electron transfer from fluorescein to anthraquinone and injection into colloidal TiO2.

A dyad-anthraquinone-methyl ester of fluorescein-and its model compound-butyl ester-were synthesized. The effects of photo-induced electron transfer from fluorescein to an organic anthraquinone acceptor and injection into inorganic colloidal TiO(2) were studied respectively. It is found that the photo-induced electron transferring to an organic acceptor is much faster than injecting into inorganic colloidal particles when fluorescein was excited by visible light. While inorganic colloidal TiO(2) was excited by UV, the electron of fluorescein will inject into TiO(2).

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PubMed2002

Effects of flow on measurements of interactions in colloidal suspensions.

A hydrodynamic mechanism of interactions of colloidal particles is considered. The mechanism is based on the assumption of tiny background flows in the experimental cells during measurements by Grier et al. Both trivial (shear flow) and nontrivial (force propagation through viscous fluid) effects are taken into account for two colloidal particles near a wall bounding the solvent. Expressions for the radial (attractive or repulsive) forces and the polar torques are obtained. Quantitative estimates of the flow needed to produce the observed strength of attractive force are given; other necessary conditions are also considered. The following conclusion is made: the mechanism suggested most likely is not responsible for the attractive interactions observed in the experiments of Grier et al.; however, it may be applicable in other experimental realizations and should be kept in mind while conducting colloidal measurements of high sensitivity. Several distinctive features of the interactions due to this mechanism are identified.

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PubMed2002

Development of effective Stokesian dynamics method for ferromagnetic colloidal dispersions (cluster-based Stokesian dynamics method).

We have developed a new Stokesian dynamics (SD) method for nondilute colloidal dispersions, which enables us to reduce drastically the computation time. To verify the validity of the present method, which is called the "cluster-based SD method," three-dimensional simulations of a ferromagnetic colloidal dispersion have been carried out for a simple shear flow. The correlation function and viscosity have been evaluated to compare the results obtained by the present method with those obtained by the ordinary SD method and by the method of ignoring hydrodynamic interactions between particles. The results obtained here are summarized as follows. The transient properties from an initial state obtained by the present method agree well with those obtained by the ordinary method, even if a radius r(clstr), which defines the cluster formation, is taken as a small value such as r(clstr)=1.2d (d is the particle diameter). Also, the equilibrium properties such as the pair correlation function and viscosity obtained by the present cluster-based method are in satisfactory agreement with those obtained by the ordinary SD method. Furthermore, the cluster-based method drastically reduces the computation time to about one-fourteenth to one-seventieth that of the ordinary method. It is clear from these results that the cluster-based SD method is significantly superior to the ordinary SD method for ferromagnetic colloidal dispersions for which a large model system such as N=1000 or 10,000 is indispensable in simulations.

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PubMed1983

Effect of 99mTc-Sn-colloid incubation time on in vivo distribution.

The in vitro particle size of 99mTc-Sn-colloid preparation increases with the length of incubation time after reconstitution. It was found that the percentage of particles trapped (T) by a 1-micron filter as a function of time (t) could be represented by the logarithmic equation T = 5.3 + 15.7 ln t (r = 0.96). This material was applied to a crossover study involving 25 patients each of whom received preparations of the same reconstituted 99mTc-Sn-colloid that had been incubated for 15 min and (each patient received both) 5 h. It was found that there was a significant shift of radioactivity to the spleen and a significant decrease in background with the material that had been incubated longer. The 99mTc-Sn-colloid is adequate for the disclosure of space-occupying disease in the liver and spleen, but unreliable for drawing conclusions on the status of liver function based on the changes in splenic concentration.

Adult↗

PubMed1992

Autometallographic silver-enhancement of colloidal gold particles used to label phagocytic cells.

The present paper demonstrates that colloidal gold silver-enhanced by autometallography (AMG) can be used to label phagocytic cells for light microscopic detection. Cultured macrophages were exposed to 0.5 microliters 6 nm colloidal gold particles for 24 or 48 h. Other cultures were exposed to 25 microliters of the same solution for 1 to 14 days. The staining was found to be stable also when new unmarked cells were applied. The colloidal gold had no adverse effect on the cells. The presented technique might also prove valuable for estimation of the total number of phagocytes in a culture or in an organism by applying labelled cells to culture or organism, and to ascertain the fate of a population of marked cells.

Animals↗