Effect of electrolyte type on the electrokinetic behavior of sulfonated polystyrene model colloids

Sulfonated polystyrene latex particles were prepared by a two-stage shot-growth emulsion polymerization process in the absence of emulsifier. Sodium styrene sulfonate (NaSS) was used as an ionic co-monomer to produce a series of latex particles with the same particle size but with different surface charge densities. The electrophoretic mobility of this functionalized model colloid was studied in the presence of various types of inorganic electrolytes. The _e curves of these latexes exhibit a pronounced maximum at high electrolyte concentrations: 5·10^–2 M for 11 electrolytes and 10^–2 M for 21 and 12 electrolytes. When a 31 electrolyte (LaCl₃) was used, the electrophoretic mobility changed to positive values at high concentration due to the specific adsorption of lanthanum species. The experimental results for the electrokinetic characterization of these sulfonated polystyrene model colloids suggest that the surface of the particles is covered by a layer of oligomers or polymer chains which shift the shear plane toward the bulk solution, increasing the anomalous surface conductance of the polystyrene microsphere-electrolyte solution interface.     

Surface study on the rubber particles in pretreated Hevea latex system

Summary From centrifuged high-ammonia latex concentrate, a fraction which contains rubber particles of a narrow particle size distribution in a serum phase freed from any water-soluble non-rubber constituents was obtained. The electrophoretic mobility of the dialysed latex particles has been studied as a function of dry rubber content, surface pH and concentration of sodium chloride. The rubber particles were shown to have an amphoteric nature with an isoelectric point at pH 3.8. The electrokinetic study showed that the net negative charge on the rubber particle surface is derived from the carboxyl groups of the adsorbed proteins and the adsorbed long-chain fatty acids. This is in agreement with the infrared data of the rubber film. The surface charge density of the rubber particle at pH > 6 was found to be 1.43 ,µC cm^–2. The stability of the latex is briefly discussed in terms of its surface charge and compared with that of synthetic latices.

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Zusammenfassung Durch Zentrifugieren von stark ammoniakhaltigen Latex-Konzentraten wurde eine Fraktion erhalten, welche Gummiteilchen mit einer engen Teilchengrößenverteilung in einem Serum enthielt, welches frei von wasserlöslichen Nichtgummibestandteilen war. Die elektrophoretische Beweglichkeit der dialysierten Latexteilchen wurde als Funktion des Gummigehaltes, des Oberflächen-pH-Wertes und der Natriumchloridkonzentration gemessen. Die Gummiteilchen verhalten sich amphoter mit einem isoelektrischen Punkt bei pH 3,8. Die Oberflächenladung rührt von Carboxylgruppen adsorbierter Proteine und adsorbierter langkettiger Fettsäuren her. Die Oberflächenladungsdichte bei pH > 6 wurde zu 1,43 ,µC cm^–2 bestimmt. Die Stabilität wird im Zusammenhang mit der Ladungsdichte diskutiert und mit der von synthetischen Latices verglichen.

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With 7 figures and 1 table     

Adsorption of anionic surfactants on positively charged polystyrene particles II

In the case of cationic polystyrene latex, the adsorption of anionic surfactants involves a strong electrostatic interaction between both the particle and the surfactant, which may affect the conformation of the surfactant molecules adsorbed onto the latex-particle surface. The adsorption isotherms showed that adsorption takes place according to two different mechanisms. First, the initial adsorption of the anionic surfactant molecules on cationic polystyrene surface would be due to the attractive electrostatic interaction between both ionic groups, laying the alkyl-chains of surfactant molecules flat on the surface as a consequence of the hydrophobic interaction between these chains and the polystyrene particle surface, which is predominantly hydrophobic. Second, at higher surface coverage the adsorbed surfactant molecules may move into a partly vertical orientation with some head groups facing the solution. According to this second mechanism the hydrophobic interactions of hydrocarbon chains play an important role in the adsorption of surfactant molecules at high surface coverage. This would account for the very high negative mobilities obtained at surfactant concentration higher than 5×10^–7 M. Under high surface-coverage conditions, some electrophoretic mobility measurements were performed at different ionic strength. The appearance of a maximum in the mobility-ionic strength curves seems to depend upon alkyl-chain length. Also the effects of temperature and pH on mobilities of anionic surfactant-cationic latex particles have been studied. The mobility of the particles covered by alkyl-sulphonate surfactants varied with the pH in a similar manner as it does with negatively charged sulphated latex particles, which indicates that the surfactant now controls the surface charge and the hydrophobic-hydrophilic character of the surface.Dedicated to the memory of Dr. Safwan Al-Khouri IbrahimPresented at the Euchem Workshop on Adsorption of Surfactants and Macromolecules from Solution, Åbo (Turku), Finland, June 1989     

The effect of particle concentration on zeta potential in extremely dilute solutions

The electroporetic mobility of hexadecane particles in water and in very dilute CTAB solutions was measured. The technique of microelectrophoresis was applied. Zeta potential was calculated according to the Hückel formula, applying Henry's correction factors. Electrokinetic charge density was calculated according to the formula used by Delgado et al., and previously discovered empiricaly by Loeb et al. and derived mathematicaly by Ohshima et al. It was found that the particle concentration in emulsion limits their charge in solutions of very low ion concentration (10^–7:10^–6 M), because the greater the particle concentration, the smaller the extent of the ions adsorbed at the surface of one particle. The zeta potential was found to be independent of particle concentration if the ratio of the number of bulk ions to particle number is not lower than 1.6×10⁶. This ratio depends on particle size, and the value 1.6×10⁶ relates to particles of diameter 1.6 m.     

Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO₃)₃ and Cr(NO₃)₃ solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al³⁺ ions in 10^–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al³⁺ adsorption and membrane charge reversal at Al³⁺ concentration in a solution higher than 10^–6 M. The dependences of the ion selectivity on pH and Al³⁺ concentration C _Al in a solution are similar. At pH < 3 and C _Al > 10^–6 M, the _1–2 > _1–1 > _2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the _2–1 > _1–1 > _1–2 series characteristic of positively charged membranes.     

Conductivity and Electrokinetic Potential of Microcrystalline Cellulose Particles in Aqueous HCl and NaOH Solutions

The conductivity of microcrystalline cellulose (MCC) dispersions in aqueous 10^–5–10^–2 M HCl and NaOH solutions was measured as a function of the particle volume fraction by the conductometry. The dependence of the relative conductivity of MCC particles on pH of equilibrium solutions was determined using the Wagner equation. The electrophoretic mobility of MCC particles in the aforementioned solutions was measured by the microelectrophoresis, and corresponding dependences of the particle potentials on pH of aqueous HCl and NaOH solutions (pH 2–11) were calculated using the Smoluchowski and Henry equations of the electrophoresis theory. It was shown that, in the case of MCC, the Henry equation, which allows for the significant conductivity of the dispersed particles, as compared with the dispersion medium, makes it possible to calculate more accurate potential values and, consequently, to derive the (pH) dependence, which is satisfactorily consistent with the effect of the surface charge and solution ionic strength on the potential in a wide pH range.     

Electrosurface properties of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

A complex study of electrosurface properties has been performed for single-crystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and X-ray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the Γ_H⁺(pH) and Γ_OH^-(pH) adsorption isotherms of potential-determining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions.     

Effect of electrolyte type on the electrokinetic behavior of carboxylated polystyrene model colloids

Carboxylated polystyrene latex particles were prepared by emulsifier-free emulsion polymerization of styrene using an azoinitiator (ACPA), which provides carboxyl end groups on the latex surface. Two latexes were characterized using TEM, PCS, conductimetric and potentiometric titrations, and electrophoretic mobility. To determine the hydrophobic or hydrophilic character of these latexes, the maximum adsorption of a nonionic surfactant (Triton X-100) was also studied and compared with other type of latexes. The electrophoretic mobility of these functionalized model colloids was studied in the presence of various types of inorganic electrolytes. The _e curves of these latexes exhibit a smooth maximum at an electrolyte concentration of around 10^–3 and 5·10^–3 M for 11, 21 and 12 electrolytes. When a 31 electrolyte (LaCl₃) was used, the electrophoretic mobility changed to positive values at high concentration due to the specific adsorption of lanthanum species. In general, the surface characteristics of these carboxylated latexes are very different in comparison to other latexes with the same functionality because the carboxyl groups are provided by the initiator, while in most of the cases these groups are provided by ionic comonomers (acrylic, methacrylic acids, etc.) used in the copolymerization with styrene.     

Dielectric properties of cleaned and monodisperse polystyrene latexes in microwaves

The dielectric behavior (, ) of three well-cleaned monodisperse polystyrene latexes having the same particle size and the same number of chemically-bound surface groups has been studied at a fixed microwave frequency (9.4 GHz), as a function of temperature and surface group (SO ₄ ^– , COO^–, OH).A large dielectric relaxation was observed in the sulfate-stabilized latex, which has the most polar surface end-group. The anomalous behavior in the thermal dependence of the hydroxyl and carboxyl-stabilized latexes (the OH latex being more pronounced than the COO^– latex) may originate from differences in the experimental conditions used for the preparation of such polymer colloids, or due to the presence of ionic species.On the basis of various dielectric models, the apparent volume fractions of the latexes were calculated. The amount of bound water around the latex particle was quantitatively correlated to the polarity of surface end-group (SO ₄ ^– > COO^– > OH). The differences between the calculated and actual values were not only a reflection of the thickness of vicinal water, but could also be indicative of the presence of oligomeric species in the suspension's medium (serum) of the latex. The permittivities of hydrated particle and of bound water were obtained with a non-linear iterative procedure.     

Adsorption of cationic polyelectrolyte onto a model carboxylic latex and the influence of adsorbed polycation on the charge regulation at the latex surface

 Adsorption of a well-characterized cationic polyacrylamide (CPAM) onto the surface of a model colloid (monodisperse polystyrene latex with carboxylic functional groups) was studied over a wide range of pH (4–9) and KCl concentration (c _s =10^-3–0.3 M). The surface charge density of the latex particles with and without adsorbed CPAM was also measured over the same range of electrolyte compositions. The adsorbed amount of CPAM increases with increase in c _s and pH. The polyelectrolyte adsorption alters substantially the surface charge density of the latex particles as compared to the polymer-free case. A large overcompensation of the surface charge by the adsorbed polyelectrolyte is established at high c _s and low pH. A qualitative explanation of the observed features is put forward. Received: 3 December 1996 Accepted: 20 January 1997     

Adsorption of Cationic Polyelectrolyte on Quartz from Aqueous Background Electrolyte Solution at pH 3

Adsorption isotherm of cationic polyelectrolyte, poly(styrene-co-dimethylaminopropylmaleimide), (molecular mass is 2 × 10⁴) on the surface of fused quartz in aqueous 10^–4 M KCl solution at pH 3 was measured by the method of capillary electrokinetics. The limiting coverage of adsorption layer corresponds to surface charge ₀ = 0.82 C/mol that exceeds the value obtained earlier at pH 6.5. However, if one takes into account the higher charge of a macromolecule at pH 3, the values of packing density of copolymer molecules in completely filled adlayers appeared to be close: 7.88 × 10¹⁰ at pH 3 and 7.27 × 10¹⁰ cm^–2 at pH 6.5. The average binding energy of the molecules and the quartz surface calculated by the Langmuir equation is equal approximately to 21kT and lies between the values of the energy of electrostatic (25.4kT) and hydrophobic (17.7kT) adsorption at pH 6.5 calculated earlier. It can be assumed that, at pH 3, charged units of a macromolecule form ion–dipole bonds with silanol groups, while uncharged groups form hydrophobic bonds with siloxane surface sites.     

The effect of metallic cations on the electrophoretic properties of a pretreatedHevea latex

High-ammonia latex concentrate prepared from doubly-centrifuged fieldHevea latex was exhaustively dialysed to remove any residual water-soluble non-rubber constituents. The electrophoretic mobilities of the dialysed latex in the presence of various metallic cations were investigated as a function of electrolyte concentration. The mobility decreased with increasing concentration of the cations Na⁺, Ba²⁺, Mg²⁺ and Ca²⁺ in a manner consistent with the effect of simple electrolyte on compression of the electric double layer. Anomalous behaviour was noted for the divalent ion copper, in that it reversed the charge of the latex particles at a concentration even lower than that of uranyl ions. Multivalent cations (lanthanum, cerium and thorium) had a profound influence on the latex particles where very low charge reversal concentrations were observed. It is believed that strong adsorption of hydrolysed species from the metallic ions was responsible for reversing the charge of the originally negative latex particles. These experiments indicated that the efficiency with which the cations reversed the charge of the latex particle surface was in the order: lanthanum > cerium > copper > thorium > uranyl > calcium > magnesium > barium > sodium. The number of cation binding sites on the latex particle surface and the chemical free energies of cation adsorption were calculated. It was found that the interaction of the latex particle with the hydrolysable metallic cations was much more stronger than that with the simple divalent cations and that this intercation was comparable to that of biological surfaces.     

Polymer adsorption on fine particles; the effects of particle size and its stability

The effects of particle size on polyacrylamide (PAAm,M _w =59×10⁴, 500×10⁴) adsorption were investigated using a series of well-characterized hematite (-Fe₂O₃) dispersions. The -Fe₂O₃ particles with highly monodisperse and nearly spherical shape ranged in radius from 23 nm to 300 nm. the maximum amount of PAAm adsorption (M _m ) in each system, showed a steady increase with decreasing particle radius and was influenced strongly by particle concentrations in the medium. Furthermore, it was realized that the diameter of -Fe₂O₃ particles after treatment with PAAm under different particle concentrations decreased with increasing particle concentration. The relation between particle concentration in the medium and particle size after treatment was also influenced by the medium pH, i.e., at the medium pH close to the isoelectric point of -Fe₂O₃ particles (pH^o=9.2), the particle size after treatment increased with increasing particle concentration. All these results suggest that in the system of ultra-fine particles, the mixing process between particle-particle and polymerparticle will play an important role on the conformation of adsorbed polymer layer.     

Study of the colloidal stability of an amphoteric latex

We have studied the colloidal stability of an amphoteric latex (–COOH and NH ₂ surface groups) with a low-angle light scattering technique (nephelometry). Measurements were carried out at different pH values and electrolyte concentrations (NaCl or CaCl ₂). The results show a behaviour in agreement with DLVO theory when the pH of the medium is below the isoelectric point (i.e.p.) of the latex: at low ionic strengths the latex is stable, but it becomes completely unstable and coagulates when electrolyte concentration goes over a particular value (the critical coagulation concentration). However, when pH is raised above the isoelectric point, the latex is completely stable even at high electrolyte concentrations, showing a behaviour clearly opposite to the theory. This could be explained by means of an additional short-range repulsive "hydration force" due to the structure of water molecules that accompany hydrated cations around the hydrophilic latex surface. The morphology and electrical properties of the latex surface have been studied by different methods: dynamic light scattering, electrophoretic mobility, potentiometric and conductometric titrations.     

Effect of divalent cations on the adhesion rate of cellular surfaces with ionizable groups

The adhesion rate of cells under charge regulation onto a rotating disc with constant potential is investigated theoretically in this paper. In particular, the effect of the presence of divalent carions in the suspension medium on adhesion rate of cells is discussed. By using sheep leucocytes as an illustrative example, it is shown that the presence of divalent cations in the suspension medium has the effect of decreasing the adhesion rate of cells. At a fixed level of ionic strength, the adhesion rate decreases with the increase of the concentration of divalent cations in the suspension medium for the various values of Peclet number andAd parameter given in this paper. For a fixed concentration of cations, the adhesion rate increases with the increase of ionic strength. At high ionic strength, the effect of increasing the concentration of cations on decreasing the adhesion rate of cells is not as high as that at low ionic strength. Applying the concept of Donnan potential, it is found that the magnitude of the electrostatic force between an ion-penetrable cell membrane and a solid surface is much smaller than that for the ion-impenetrable cell membrane.Nomenclature a cell radius (cm) - A Hamaker's constant (erg) - Ad A/kT - C dimensionless cell concentration - D cell diffusion coefficient (cm²/s) - e magnitude of electron charge (statcoul) - F dimensionless interaction force between cell and rotating disc pernkT - h minimum separation distance between cell surface and disc surface (cm) - H dimensionless separation distance between cell surface and disc surfaceh/a - [H ⁺] _r hydrogen ion concentration in the suspension medium (mole dm^–3) - [H ⁺] _s hydrogen ion concentration on the cell surface (mole dm^–3) - Boltzmann's constant (erg K^–1) - K _a dissociation equilibrium constant for acid groups on cell surface (mole dm^–3) - K _b dissociation equilibrium constant for base groups on cell surface (mole dm^–3) - n ionic strength in the suspension medium (ions cm^–3 - Pe Peclet number - q valence of cations - Sa the reciprocal of acidic density on the cell surface (cm²/group) - S _b the reciprocal of basic density on the cell surface (cm²/group) - Sh Sherwood number - T absolute temperature (K) - the fraction of cationic electrolyte in the suspension medium, 01 - reciprocal of Debye length, (cm^–1) - fluid kinematic viscosity (cm²/s) - ×a - l distance between two plate surfaces in Derjuguin's model (cm) - dimensionless total interaction energy between cell surface and disc surface - _vdw dimensionless unretarded van der Waals potential between cell surface and disc surface - _DL dimensionless double-layer interaction potential between cell surface and disc surface - dimensionless electrostatic potential between cell surface and disc surface - rotating speed of the disc (rad/s)     

Effects of dissolved metal chlorides on the behavior of silica nanoparticles in aqueous media

Effects of chlorides of univalent (LiCl, NaCl, KCl), bivalent (MgCl₂, BaCl₂) and trivalent (AlCl₃) metals at different concentration (0.001–0.1 M) on the behavior of nanosilica A-200 (0.5–5 wt.%) in aqueous media are analyzed using photon correlation spectroscopy (particle size distribution, PSD), electrophoresis (zeta potential ζ), potentiometric titration (surface charge density), and estimation of screening length of primary particles and their aggregates. The zeta potential and the PSD are affected by silica content, pH, and concentration and type of dissolved salts. Smaller but more strongly hydrated Li⁺ cations caused stronger nonlinear dependences of the zeta potential on pH and salt content than Na⁺ or K⁺. This nonlinearity is much stronger at a lower content of silica (0.5–1 wt.%) than at C _A-200 = 2.5 or 5 wt.%. At a high concentration of nanosilica (5 wt.%) the effect of K⁺ ions causes stronger diminution of the negative value of the zeta potential due to better adsorption of larger cations. Therefore, the influence of K⁺ on increasing screening length is stronger than that of Na⁺ for both primary nanoparticles and their aggregates. A similar difference in the ζ values is observed for different in size cations Ba²⁺ and Mg²⁺.      

Ethylenediamine and Hydroxyethylenediamine Complexes of Zinc(II): A Potentiometric Study of Composition and Stability

The equilibrium potential of saturated zinc amalgam is studied as a function of concentration of free ethylenediamine molecules, [en], in the region [en] 0.001–1 M in solutions of pH 9.5, 10.5, and 11.5. At the concentration of zinc(II) ions 2 × 10^–3 M and [en] = 1 M only simple trisethylenediamine complexes of zinc(II) form in all the solutions. At smaller [en] and pH 9.5 and 10.5, complexes Zn(en)₂ ²⁺ and Zn(en)₂OH⁺ are also present; these are complemented at pH 11.5 by Zn(en)₂(OH)₂ at [en] 0.005–0.1 M. Stability constants for these complexes are calculated.     

Zeta potential and surface charge density of polystyrene-latex; comparison with synaptic vesicle and brush border membrane vesicle

The electrophoretic mobility of polystyrene — latex (PSL) of diameter 870 Å was determined using a Laser Zee System 3000. This instrument enables automatic measurement of the electrophoretic mobility of fine particles. Effect of pH and ionic strengthI on the PSL mobility was analyzed. It was found that the mobility as a function of pH has a minimum around pH 3–4 atI=0.1, showing no isoelectric point, and that the mobility decreases with increasing ionic strength up toI=0.1 but is almost constant forI=0.1–0.2 at pH=7.34. From the mobility date, we estimated the zeta potential of PSL. We used an approximate mobility formula derived by Ohshima, Healy and White, which is considerably more accurate than Smolchowski's and Henry's formula and is applicable for fine particles with small a ( a10), where is the Debye-Hückel parameter anda is the particle radius. Further, we calculated the surface charge density of PSL using an approximate relationship. It was found that there are 2000–4000 negative charges on the PSL surface at pH=7.34. Comparison is made with the results on synaptic vesicles (SV) from brain cerebrum cortex and brush-border-membrane vesicles (BBMV) from the small intestine.     

Determination of thorium isotopes in seawater by using preconcentration of thorium-XO complexes on XAD-2 resin

Thorium isotopes in seawater are determined by means of adsorption of the Xylenol Orange /XO: H₆A/ complex onto XAD-2 resin at pH=3 and the XO concentration of 10^–5M, and subsequent purification using an anion-exchange resin, and finally with alpha-spectrometry. The dissolved²³²Th concentration in the western North Pacific surface water is found to range from 0.8 to 1.2 Bq ^–1. The adsorbed species of the Th-XO complex under the experimental conditions has a composition of Th/H₂A/₂ according to the mass balance analysis.     

Synthesis, characterization and potential biomedical applications of N-succinimidyl ester functionalized, polypyrrole-coated polystyrene latex particles

N-Succinimidyl ester functionalized polypyrrole-coated polystyrene latex particles (PS_E-PPyNSE) were prepared by the in situ copolymerization of pyrrole and the active ester-functionalized pyrrole (pyrrole-NSE) in the presence of polystyrene latex particles. Polystyrene microspheres were prepared by emulsion polymerization (PS_E) leading to particles having a diameter of 450 nm. These PS_E particles were precoated with poly(N-vinylpyrrolidone) prior to the in situ copolymerization of pyrrole and pyrrole-NSE. The initial comonomer concentration fractions were 25/75, 50/50 and 75/25 for pyrrole and pyrrole-NSE, respectively. The PPy-coated PS_E particles were characterized in terms of morphology, particle size, electrophoretic mobility and chemical composition. The study of morphology by means of scanning electron microscopy showed roughening of the underlying PS_E particles owing to the addition of PPyNSE, the overlayer thickness of which was estimated to be around 7 nm. Moreover, loading PPyNSE overlayers resulted in a shift of the electrophoretic mobility from –5.31 m cm/V s to a very small but positive value (0.082–0.112 m cm/V s). X-ray photoelectron spectroscopy and IR spectroscopy permitted the detection of pyrrole-NSE repeat units at the surface indicating that pyrrole and pyrrole-NSE did indeed copolymerize. The PS_E-PPyNSE particles were further evaluated as bioadsorbents of human serum albumin used as a test protein. For this study, PS_E-PPyNSE₅₀ particles, synthesized from a comonomer feed ratio of 50/50 in pyrrole/pyrrole-NSE, were used and were shown to attach efficiently human serum albumin macromolecules with a maximum amount of 0.2 mg m^–2.