Polystyrene Sulfate Latex Research Articles

Effects of ionic valence on aggregation kinetics of colloidal particles with and without a mixing flow

Hypothesis: The classical Schulze-Hardy rule states that the critical coagulation concentration (CCC) of colloidal particles is inversely proportional to the counter-ionic valence at powers ranging from 2 to 6. However, the inverse Schulze-Hardy rule has recently been proposed, suggesting that the CCC can also be inversely proportional to the co-ionic valence. Previous studies on these rules did not consider the effect of flow on aggregation kinetics and the CCC. This study aims to investigate the effect of multivalent counter-ions and co-ions on aggregation kinetics and the CCCs in systems with and without a mixing flow.Experiments: We measured the aggregation rate coefficients of polystyrene sulfate latex particles as a function of the salt concentration with different ionic species. Furthermore, we analyzed these measurements using theoretical models based on hydrodynamic pair-diffusion in a random flow and trajectory analysis in two steady flows. The analysis was conducted using zeta potentials determined through electrophoretic measurements.Findings: Although the trajectory analysis underestimates the CCCs, the hydrodynamic pair-diffusion model can capture the shift of critical coagulation concentrations in the mixing flow to higher values than those in Brownian aggregation and also shows a better agreement with the experimental results. This result suggests that combining random flow and Brownian diffusion is crucial for developing a consistent framework for predicting both Brownian aggregation and aggregation in a mixing flow.

Shielding behavior of electrokinetic properties of polystyrene latex particle by the adsorption of neutral poly(ethylene oxide)

To understand the shielding of electrokinetics of colloidal particles by polymer coating, we measured the electrophoretic mobility of negatively charged polystyrene sulfate latex (PSL) adsorbed with electrostatically neutral polyethylene oxide (PEO) chains with various molecular weights under different ionic strengths. We confirmed that substantial adsorbed neutral polymer on the particle surface would decrease the absolute value of electrophoretic mobility. Even though the polymer layer is sufficiently thicker compared to the thickness of electric double layer (EDL), the electrophoretic mobility (EPM) never vanishes, which indicates the incompleteness of electrokinetic shielding by an adsorbed neutral polymer. To relate such interesting phenomena, a simple mathematical model has been proposed to evaluate the electrophoretic mobility, assuming the presence of a scaling structure of adsorbed permeable polymer layer does not influence the Poisson–Boltzmann distribution of ions in the electric double layer (EDL). An analytical expression of electrophoretic mobility under Debye-Hu¨ckel approximation has been derived using the method of Ohshima-Kondo theory, which successfully justifies the experimentally obtained data.

Adsorption of Binary Mixture of Highly Positively Charged PTMA5M and Partially Negatively Charged PAA onto PSL Particles Studied by Means of Brownian Motion Particle Tracking and Electrophoresis

Effects of ionic strength on the adsorption of highly charged polycationic ((2-dimethylamino)ethyl methacrylate) methyl chloride quaternary salt (PTMA5M) individually as well as in a binary mixture with polyanionic acrylic acid (PAA) onto polystyrene sulfate latex (PSL) particles with negative charges were investigated by means of Brownian movement particle tracking and measurement of electrophoretic mobility. In addition, the adsorption mechanism was confirmed by Fourier transform infrared (FT-IR) and energy-dispersive X-ray (EDX) spectroscopic methods. The hydrodynamic thickness of the adsorbed polyelectrolyte layer (δH) and electrophoretic mobility (EPM) of particles as a function of concentration ratios of the two polyelectrolytes were measured to clarify the effect of negatively charged molecules on the structure of the positively charged adsorbed layer at various ionic strengths. Extremely thick δH was confirmed for the case of excess dosage of polycations. The δH decreased more significantly with the addition of PAA than increasing ionic strength. Interestingly, in the presence of PAA, the adsorbed layer thickness increased more at lower ionic strength than at higher ionic strength. In addition, the initial δH decreases remarkably after a time lapse of 1 h. Contrary to the decrease of the δH, almost all EPM either remained unchanged or increased over time depending on the concentration ratio of the two polyelectrolytes. Constant charge density, desorption of polyanions, and then reconformation of the adsorbed polycationic layer are proposed model components.

Temporal Changes of Adsorbed Layer Thickness and Electrophoresis of Polystyrene Sulfate Latex Particles after Long Incubation of Oppositely Charged Polyelectrolytes with Different Charge Densities.

The different desorption concepts of the two polyelectrolytes PTMA5M and PTMC5M, which have similar molecular weights and differ in the charge density on the polystyrene sulfate latex (PSL) particles by 25 times, and with various charge densities in a long incubation, were systematically investigated based on hydrodynamic adsorbed layer thickness (δH) and electrophoretic mobility (EPM) under two ionic strengths in the present study. Herein, in the case of highly charged polyelectrolyte PTMA5M, desorption continued for 4 h and re-adsorbing proceeded after a longer incubation time higher than 4 h. Meanwhile, in the case of lowly charged polyelectrolyte PTMC5M, an adsorption–desorption equilibrium was suggested to take into account the unchanging of both δH and EPM.

Adsorption of Poly(acrylic acid) onto Negatively Charged Polystyrene Sulfate Latex Particles by Means of Particle Tracking of Brownian Motion, Electrophoretic Mobility and Fourier Transform Infrared Spectroscopy

The adsorption of poly(acrylic acid) (PAA5K) with negative charge on the highly negatively charged polystyrene sulfate latex (PSL) particles at various ionic strengths were investigated in the present study. The adsorption of PAA was promoted with high ionic strength while the driving forces were mainly controlled by the non-electrostatic interactions including hydrogen bondings, dipole–ions and dipole–dipole. The adsorbed layer thickness of PAA on PSL and electrophoretic mobility of PSL in the presence of PAA increased with increasing ionic strength. In case of adsorption of 5 ppm PAA, the adsorbed layer thickness increased slightly about 2 times corresponding with 41.3 to 80.4 nm while the electrophoretic mobility of PSL changed from –4.87 to –6.31 μm cm/(V s) with increasing 100 times of the ionic strength from 0.1 to 10 mM KCl. The change of surface functional groups of PSL after PAA adsorption was thoroughly determined by Fourier transform infrared (FTIR) spectroscopy. The distinction between the electrostatic and the non-electrostatic interaction which contributed to the adsorption of PAA on the PSL particles and the adsorbed polymer conformations at different salt concentrations was clearly clarified. We demonstrate that the adsorbed PAA conformations were more vertically swollen at the PSL solid–solution interface.

Relaxation of adsorbed layer thickness and electrophoresis of polystyrene latex particles after overshooting of polyelectrolytes with different charge density

Temporal change of hydrodynamic layer thickness (δH) and electrophoretic mobility (EPM) of polystyrene sulfate latex (PSL) particles adsorbed by oppositely charged polyelectrolytes were monitored herein to clarify the relaxation behavior after overshooting. Two linear polyelectrolytes with nominal molecular weight of 5 million differing in chain charge density, σ = 100 % (PTMA5M) and σ = 4 % (PTMC5M), and PSL particles of different diameters were used in the experiment. With the former polyelectrolyte, a remarkably thick layer that is formed at the incubation decays with the time scale of several tens of minutes and the EPM remains constant. The value of δH decreases with the increase of particle size, whereas with the latter polyelectrolyte, the initial value of δH is several times smaller than that of the former. There is a case wherein the EPM decreases with time, although δH remains constant. The initial δH is independent of the particle size. Ascribing the reason for the relaxation phenomena to desorption of overshot polyelectrolytes attached with meta-stable conformation in the initial stage, we have obtained an approximate picture of the conformational change for the chain of different charge density.

Electrophoretic mobility of latex spheres in mixture solutions containing mono and divalent counter ions

The electrophoretic mobilities of polystyrene sulfate latex spheres carrying constant surface charge densities in aqueous solutions were measured in the presence of monovalent K+ and divalent Mg2+ counter ions. The measurements were carried out as functions of the concentrations of Mg2+ and K+ ions (CMg and CK) and the ratio of the concentration of divalent counter ions to that of monovalent ions, X=CMg/CK. The data were analyzed on the basis of standard electrokinetic and electric double layer models. The calculated values of the mobility are in reasonably good agreement with the experimental data assuming that the distance of the slipping plane from the surface, xs ranges from 0 to 0.25nm and the values of xs increase with increasing X.

Breakup and strength of polystyrene latex flocs subjected to a converging flow

Breakup of flocs (aggregates of colloidal particles) in converging flows is encountered in many industrial processes such as filtration, pipetting for sampling of flocs, and mechanical dispersion. The experiment of breakup of flocs by a converging flow opens the possibility to obtain the strength of floc against breakup. The quantity is crucial for controlling flocculator in water treatments and predicting transport of colloidal particles in aqueous environments. Therefore, the mechanism of disaggregation of flocs subjected to a converging flow is emerging as an interesting theme from engineering and scientific points of view. Recently, Blaser evaluated the hydrodynamic disrupting force on a floc in an axisymmetrical straining flow. In the present study, to confirm the validity of the ellipsoidal model proposed by Blaser and to obtain the strength of latex flocs in a simple electrolyte solution, polystyrene sulfate latex (PSL) flocs formed in a simple KCl solution were disrupted by a converging flow of the solution. Experimental data of relationships between floc size and volumetric flow rate were analyzed by assuming flocs hydrodynamically behave like solid ellipsoids to evaluate strength of flocs. The obtained floc strength was 2nN in average and did not depend on floc size. When the values of floc strength of this study were compared with those of previous researches, they were found to be 1–2 orders smaller than strengths of flocs formed by the addition of polymer flocculants and/or precipitated ferric or aluminum hydroxide coagulants evaluated by similar methods. This result is reasonable because flocculants and coagulants are usually used to increase floc strength in water and wastewater treatments. The value of obtained floc strength was also comparable to the pull-off force between latex particles in water by means of colloid probe atomic force microscopy (AFM) by Hodges et al. However, the obtained floc strength was 1–2 orders of magnitude smaller than the pull-off force between latex particles as found with colloid probe AFM by Li et al.

Effect of floc structure on the rate of shear coagulation

We derived a mathematical expression for the temporal evolution of the number of particles due to shear coagulation, covering the later stage by expanding the initial stage approximation to take into account the formation of floc structure. In the derivation, it is assumed that flocculation proceeds through binary collisions between identical fractal flocs. The capture efficiency between flocs is calculated on the basis of trajectory analysis, which is determined by viscous hydrodynamic interaction between flocs and van der Waals attractive forces between two primary particles located at colliding points of flocs. The validity of the derived equation was tested by a coagulation experiment using polystyrene sulfate latex particles under conditions of rapid coagulation. The experiment was carried out in a laminar Couette flow generated in the gap between two concentric cylinders. Careful and direct observation of flocculation under microscopy provided the data on the fractal dimension as well as the temporal evolution of number concentration of flocs. The measured rate of coagulation gradually increases in accordance with the formation of the fractal structure of flocs. This behavior agreed very well with the prediction based on the derived equation.

Measuring a colloidal particle's interaction with a flat surface under nonequilibrium conditions. Total internal reflection microscopy with absolute position information.

A new and general approach is proposed to analyze the dynamics of a colloidal particle interacting with a nearby wall. This analysis can be used to determine the acting forces even when the system is non-stationary. As an illustration, we use total internal reflection microscopy to investigate the forces acting on a polystyrene sulfate latex particle as it is receding from a charged glass surface.

The significance of stagnant layer conduction in electrokinetics

This paper examines the consequences of the occurrence of conduction processes in the stagnant fluid layer between the surface of a colloidal particle and the shear plane when it is undergoing an electrokinetic process. It is shown that the most widely used model system for studying electrokinetics (viz. monodisperse polystyrene sulfate latex) displays significantly different behaviour in different experiments depending on the details of the post-polymerisation clean-up procedure. Nonetheless, the results provide important insights into how electrokinetic results should be interpreted. A procedure is suggested which should allow a more realistic evaluation of the diffuse double layer potential from electrokinetic results without the need for extensive conduction studies.

Polystyrene Sulfate Latex Particles in the Presence of Poly(vinylamine): Absolute Aggregation Rate Constants and Charging Behavior

Absolute aggregation rate constants of anionic polystyrene sulfate latex particles were measured in the presence of cationic poly(vinylamine) by time-resolved simultaneous static and dynamic light scattering. The colloidal stability depends sensitively on the polymer dose, pH, and ionic strength. While the stability ratio is strongly dependent on the ionic strength, the electrophoretic mobility depends much more weakly on it, and therefore the latter measurements cannot be used as a reliable measure of the suspension stability. In the fast aggregation regime, the presence of the oppositely charged polyelectrolytes leads to an enhancement of the aggregation rate with respect to the one in the presence of an indifferent electrolyte. This acceleration probably originates from attractive electrostatic interactions between surface charge heterogeneities.

Effect of Gravity on Colloidal Deposition Studied by Atomic Force Microscopy

Atomic force microscopy (AFM) was used to study the effect of gravitational forces on the deposition of submicrometer colloidal particles onto solid surfaces to test the usual assumption that the contribution of gravity to the behavior of particles with diameters <1 μm is negligible. The effects of both particle size and density were examined using polystyrene sulfate latex, silica, and colloidal gold particles of several sizes ranging from 10 nm to 1 μm. The results show that significant differences are observed in the deposition of colloidal particles onto horizontal and vertical surfaces, under identical suspension conditions and exposure times, showing that gravitational forces can have a considerable effect. This effect was quantified by analysis of the AFM images. The experimental results are compared to calculations of the expected coverage and particle surface concentration assuming diffusion-limited adsorption and deposition by sedimentation. Gravity can be negligible for low-density particles with diameters considerably smaller than 1 μm. However, if the density of the colloidal particles is high, as in the case of colloidal gold, gravity can become a significant driving force for particle transport to the surface, even for particles with diameters much smaller than 100 nm.

Zeta Potential of Highly Charged Thin Double-Layer Systems

Electrophoretic measurements under d.c. conditions involve a fundamental ambiguity for particles with a high zeta potential; two very different values of zeta potential can be ascribed to the same mobility. In the case of a polystyrene sulfate latex studied previously, selecting the higher (absolute) value gave a more consistent picture of the interface and also removed an anomaly in the electrokinetic behavior as a function of indifferent electrolyte concentration. Confirmation that the higher value is the correct one, however, was still needed. The ambiguity is resolved unequivocally here by the use of high-frequency mobility measurements using electroacoustics, since the mobility spectra for the high and low zeta potentials are very different. The interpretation is supported by the dielectric relaxation spectra of this material in the megahertz region.

Membrane Filtration for Microencapsulation and Microcapsules Fabrication by Layer-by-Layer Polyelectrolyte Adsorption

Layer-by-layer polyelectrolyte adsorption at colloid particle surfaces as well as the removal of the core latex to obtain multilayer microcapsules is conducted by means of membrane filtration. As target particles for adsorption we use nonsoluble polystyrene sulfate latex, soluble melamine formaldehyde resin latex, and decomposable glutaraldehyde fixed human red blood cells. The materials adsorbed are poly(allylamine hydrochloride), poly(styrenesulfonate), poly(diallyldimethylammonium chloride), chitosan, and chitosansulfate. The coating process is carried out under different membrane filtration conditions with respect to the pressure regime, the filter materials, and the stirring conditions. We characterize the prepared multilayers at the particle surface or in the microcapsule (shell) form by atomic force microscopy, confocal laser scanning microscopy, transmission electron microscopy, single-particle light scattering, and electrophoresis. The quality, performance, and yield of the presented method are c...

Low-Frequency Dielectric Response of Polystyrene Latex Dispersions

The low-frequency permittivity and the conductivity increments of a well-characterized polystyrene sulfate latex with constant surface charge density were measured in KCl electrolyte solutions. The ionic strength was varied in the range 0.4–6 mM. The data could be explained with one absolute surface-conductivity parameter over the complete concentration range. The titratable surface charge density correlates well with the surface conductivity, the ions in the double layer having the bulk mobility. The results are in good agreement with static conductivities of plugs composed of the same particles obtained in a previous study (1). The electrokinetic charge obtained from streaming potentials (1) in that study is significantly lower, confirming the presence of conduction behind the shear plane. In order to interpret the conductivity data, simple analytical expressions have been derived for the frequency-dependent complex conductivity of a dilute dispersion of spherical particles with relatively thin double layers (κa⪢1, whereais the particle radius and κ−1the Debye screening length). The expressions are restricted to binary suspending electrolytes. However, no restrictions on the ion mobilities and ion valencies are made. Our results agree well with the numerical results of the dielectric model of Mangelsdorf and White (2,3) and reduce to O'Brien's static conductivity results (4) in the limit of low frequencies.

Streaming Potentials and Conductivities of Latex Plugs in Indifferent Electrolytes

Streaming potential and conductivity measurements were performed on porous plugs in a number of indifferent electrolytes. The plugs were made of monodisperse spherical polystyrene sulfate latex with fixed surface charge density. The observed surface conductivity could be interpreted with the classical Bikerman expression extended with the contribution from conduction behind the shear plane. It was shown that electroosmosis contributes positively, while the depletion of co-ions in the double layer contributes negatively to the surface conductivity. It was further demonstrated that a significant part of the conduction is located behind the slip plane. The ion mobility of the indifferent counterions behind, as well as beyond, the shear plane is close to the bulk mobility. In the correct determination of ζ-potentials in the low electrolyte concentration range, it is necessary to take surface conduction behind the plane of shear into account. When this is done, the maximum in the curve of the ζ-potential versus electrolyte concentration disappears.

Kinetics of Heterocoagulation

The heterocoagulation of colloids A and B was investigated by computer simulation and through experiments. In simulation, the cluster aggregation ability Å n , and cluster size n were correlated using the equation A n = A 1 n gamma; , and the three situations, γ = -0.5, 0, and 0.5 were investigated. The scaling laws of aggregation kinetics were established and the exponents were expressed as a function of the relative concentration x = [A]/([A] + [B]) of the two latices. A unique master curve represented the correlation between the temporal variations of the weight S( t) and number N( t) average sizes. On the contrary, the correlation between the exponents of the dynamic scaling laws and the relative concentration x depended on x. In the experiments, a particle counter technique was used to determine the aggregate concentration c n ( t) as a function of the aggregate size n, thereby allowing the aggregate average sizes S( t) and N ( t), which were directly compared to those obtained from simulation, to be calculated. In the heterocoagulation experiments, mixtures of polystyrene amidine latex (A) and polystyrene sulfate latex (B) of equal size, which exhibited identical electrophoretic mobility at the pH of the experiments, developed different aggregation modes. For x ⪡ 0.5, the process resembled an irreversible diffusion-limited aggregation. For x equal or close to 0.5, S( t) and N( t) increased with the features of a reversible process. Finally, for x ⪢ 0.5, the rate of the process is enhanced. Our experiments also showed that sulfate latex constituted the core of the aggregate and that the amidine latices were located around them.