Amphoteric Latex Research Articles

The role of metal ion-ligand interactions during divalent metal ion adsorption

A suite of seven different divalent metal ions (Ca(II), Cd(II), Cu(II), Mg(II), Ni(II), Pb(II), Zn(II)) was adsorbed from solution onto two Fe2O3 samples, quartz SiO2 and three different amphoteric polystyrene latices (containing amine and carboxyl functional groups). For the metal oxides, a high correlation was observed between the pH at which 50% of the metal was removed from solution (pH50) and the first hydrolysis constant for the metal ion (pK1). For the polystyrene latices, a much higher correlation was observed between the pH50 and pKc (equilibrium constant describing metal-carboxyl affinity) as opposed to pK1. These observations provide evidence of a strong relationship that exists between a metal’s affinity for a particular ligand in solution and for that metal ion’s affinity for the same ligand present as part of an adsorbing surface. The isoelectric point of the amphoteric latex surface can be increased by decreasing the carboxyl content of the latex surface. For all 7 metal ions, this resulted in a substantial decrease, for any given pH, in adsorption. We suggest that this may be partly due to the decreased carboxyl content, but is dominantly attributable to the presence of less favorable electrostatic conditions. This, in turn, demonstrates that electrostatics play a controlling role in metal ion adsorption onto amphoteric latex surfaces and, in addition to the nature of the metal ion, also controls the pH at which adsorption takes place.

Electrostatic interactions between amphoteric latex particles and proteins

The electrostatic interactions between amphoteric polymethyl methacrylate latex particles and proteins with different pI values were investigated. These latex particles possess a net positive charge at low pH, but they become negatively charged at high pH. The nature and degree of interactions between these polymer particles and proteins are primarily controlled by the electrostatic characteristics of the particles and proteins under the experimental conditions. The self-promoting adsorption process from the charge neutralization of latex particles by the proteins, which have the opposite net charge to that of the particles, leads to a rapid reduction in the zeta potential of the particles (in other words colloidal stability), and so strong flocculation occurs. On the other hand, the electrostatic repulsion forces between similarly charged latex particles and the proteins retard the adsorption of protein molecules onto the surfaces of the particles. Therefore, latex particles exhibit excellent colloidal stability over a wide range of protein concentrations. A transition from net negative charge to net positive charge, and vice versa (charge reversal), was observed when the particle surface charge density was not high enough to be predominant in the protein adsorption process.

Synthesis and characterization of amphoteric latex particles

Stable monodisperse amphoteric latex particles were prepared by the semibatch surfactant-free emulsion copolymerization of methyl methacrylate and methacrylic acid (MAA) initiated by 2,2′-azobis(2-amidinopropane) dihydrochloride (V-50). These submicron particles have a net positive charge, which is attributed to the ionized amino group at low pH. In contrast, they become negatively charged owing to the ionized carboxyl group at high pH. There exists a pH at which these particles exhibit a net charge of zero (pI). At a constant level of V-50, the pI value of these latices decreases with increasing amount of MAA used in the polymerization recipe. The effect of pH on the colloidal stability of these amphoteric latices toward the addition of the negatively charged latex was investigated. The resultant coagulation kinetics was used to study the electrostatic interaction between the amphoteric particles and negatively charged particles.

Study of the colloidal stability of an amphoteric latex

We have studied the colloidal stability of an amphoteric latex (–COOH and NH2 surface groups) with a low-angle light scattering technique (nephelometry). Measurements were carried out at different pH values and electrolyte concentrations (NaCl or CaCl2). 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 Blending Ratio of Amphoteric and Anionic Latex on Print Quality of Coated Paper.

Effectiveness of amphoteric latexes was studied to solve the problems of binder migration and un-even binder distribution in coating layers. The addition of amphoteric latex was effective in improving rheological properties of coating color in alkaline region through strong interaction with other coating components. As a result, coated papers made with amphoteric latex showed better printing qualities, such as paper gloss and surface smoothness.

Amphoteric initiators suitable for emulsifier-free emulsion polymerization and the properties of the resulting latices

The soap-free emulsion polymerizations of styrene (St) and acrylamide (AAm) or methyl methacrylate (MMA) were carried out in the presence of three kinds of amphoteric initiators, and the polymerization kinetics and the colloidal properties of the latices produced were emphatically investigated. It was found that the number of carbon atoms between the amidino and carboxyl groups in each initiator exhibited an appreciable effect on the dissociation as well as on the solubility of the initiator in water, and therefore, that the properties of the colloidal particles depended on the structure of the initiators used. All the copolymerization runs, except for the polymerization using 2,2′-azobis(N-(2-caboxyethyl)-2-methylpropionamidine) under a strongly alkali condition, gave amphoteric latices, which indicated higher critical flocculation concentrations at lower or higher pHs than at a medium pH. The surface charge density measured by titration for poly(St/MMA) particles was about 3–10 times as high as that for the poly(St/AAm) ones, though these were prepared under the same conditions other than the monomer composition. The influence of the polymerization pH on both the polymerization rate and the surface charge density of the resulting latices was negligible even if the constants of the decomposition rate and the dissociation of the amphoteric initiators strongly depended on the pH of the medium.

Studies on Coated Broke Recycling in the Papermaking (1)

This study was carried out to investigate the influence of binder latex on the white water system. The coated brokes containing polystyrene-butadiene latex or polyacrylate latex were prepared from one-side coated paper based on an acidic or an alkaline paper. The effect of amphoteric latex and anionic latex on the broke recycling was studied with regard to turbidity, conductivity, fines content, cationic demand and pitch consistency of white water. When the coated brokes with the amphoteric latex were repulped, its white water had lower turbidity, fines content, cationic demand, electric conductivity, and pitch consistency than that of coated brokes with the anionic latex. These results indicate that the coated brokes with amphoteric latex had more preferable influence on the white water system than those with anionic latex.

Influence of microstructure on the dynamic mechanical behavior of polymeric composites containing structured latexes

The dynamic mechanical behavior and mechanical behavior of polymeric composites containing three different kinds of dispersed phase are discussed. The first system has a structure of island-in-island type of morphology which is formed by phase separation inside of the crosslinked latex particles. The second system has a dispersed phase with a core-shell type of morphology which is prepared by heterocoagulation of large amphoteric latex and small anionic latex. The last one makes use of hollow particles containing a central void of 0.4 μm. The surface of the hollow particle has been modified to provide chemical bonds with a matrix phase composed of epoxy resins. The effect of morphology, the characteristics of the shell and the extent of interfacial bonding on the dynamic mechanical behavior or fracture behavior are discussed.

Effects of an Inner Helmholtz Layer on the Dielectric Dispersion of Colloidal Suspensions

An inner Helmholtz layer model is proposed for the low-frequency dielectric dispersion of aqueous suspensions of submicron size colloidal particles. It is assumed that the ions in this layer are mobile but isolated from the outer layers (the outer Helmholtz layer and the diffuse layer). For relaxation frequencies of the inner Helmholtz layer much lower than those of the outer layers, the polarization of the inner Helmholtz layer is simulated using a random walk method. A Debye-type relaxation is obtained. Using parameters consistent with the range of experimental conditions, an excellent fit to data on suspensions of amphoteric latex particles is obtained, whereas the standard electrokinetic theory of diffuse double layers and the dynamic Stern layer model have both been unsuccessful in this regard. It is predicted that the polarization of the inner Helmholtz layer will become nonlinear and will saturate with applied fields at high field strength.

Behavior of Latex and Vesicle Particles at Oil/Water Interfaces

Examination was made of interactions between an oil/water interface and latex and vesicle particles by measuring adsorbance in a suspension, particle size distribution and interfacial tension. The following results were obtained.In a diisobutylketone/water+amphoteric latex system, particles were found to be transported from the water phase to oil phase. However, in cyclohexane containing AOT an increased absorbance of an aqueous suspension was observed at acidic pH. The flocculation of suspended particles would thus appear to occur through the neutralization of positive charges on the latex surface by negative charges in AOT molecules. In a diisobutylketone/PC vesicle system, increased absorbance in suspension was also noted. Analysis of particle size distribution in the suspension indicated swelling and flocculation to be accelerated by solubilization of the oil phase into vesicles. However, on using cyclohexane, the dispersion of PC vesicles was stabilized. Surface tension measurement indicated adsorbed PC at the interface to prevent direct interaction of the oil phase with PC vesiclrs.

両性ラテックスを用いた塗工層の構造解析

The structures of the coated layers containing amphoteric latices as binders, with different glass-transition temperatures (Tg), have been studied with respect to the porosity, the of latex particles and the degree of orientation of clay particles in the coated layers.In contrast with the conventional anionic latices, amphoteric latices are found to form more porous coated layer, disturb the orientation of clay particles and show restricted migrations in the coated layers, through the electrostatic interaction with clay particles when the coating colors are prepared below pH 10.These behaviors are also revealed to depend on the Tg of latices and the drying conditions of coated layersThe structural features of coated layers are discussed in connection with the properties of coated paper, e. g. gloss.

コーティングカラーの流動特性に関する研究 第６報 両性ラテックス配合カラーの物性

The electrostatic interaction between coating color components affecting the viscoelastic properties and the interfacial electrokinetic behavior of coating color system was studied by using two types of latexes with the same styrene-butadiene ratio but with different surface charges ; one containing usual anionic groups (anionic latex) and the other containing both anionic and cationic groups (amphoteric latex).The coating color containing amphoteric latex was found to have the following characteristics as compared with anionic latex : 1) The absolute value of zeta potential was remarkably decreased by lowering pH from around pH 7 and reversed to positive values below pH 4.2) Viscosity was significantly increased below about pH 7.3) Thermal treatment of the color resulted in irreversible gelation in nearly neutral conditions.These phenomena indicate that the dissociation of amino groups on the surface of amphoteric latex is dependent on the pH of the medium, thus affecting the properties of coating color through the electrostatic interaction between clay and latex or between latex particles. The important finding is that the coating color containing amphoteric latex has as similar stability and viscoelastic properties as those of anionic color in alkaline conditions, suggesting the applicability to conventional operations in color handling and color application. When applied onto base paper, however, the characteristics of the amphoteric system come into play through possible changes in pH, thus resulting in favorable features of coated paper.

コーティングカラーの流動特性に関する研究 第４報 バインダーラテックスのパルプ繊維への静電的吸着とＳＥＭによる可視化

The interaction of binder latices with the surface of coating base paper was studied by the technique of osmium tetroxide fixation combined with pH control by buffer solution. The technique, formerly applied to latex-clay systems, was found useful too in visualizing the electrostatic interaction between latex and cellulose fibers. A pulp fiber (bleached softwood kraft pulp) and three types of crystalline cellulose microfibrils (i. e., Valonia cellulose, bacterial cellulose, and cotton-derived microcrystalline powder), all having negative zeta potentials, showed strong interactions with amphoteric latex particles under acidic conditions. The intensity of interaction, as judged from the number of adsorbed latex particles, was consistent well with the order of absolute values of zeta potential. The other combinations of latex type and pH, i. e., amphoteric latex at high and anionic latex at both high and low pHs, resulted in virtually no binding between the components.These findings, together with the former observations of latex-clay systems, indicate that the use of amphoteric latex provides useful means of controlling the coating processes, i. e., prevention of binder migration or formation of bulky coating layer, through rapid immobilization of latex and/or clay particles at the base paper-coating color interface. Such interactions would also be useful in other areas of paper manufacture including internal sizing or off-machine latex impregnation.

コーティングカラーの流動特性に関する研究 （第５報） コーティングカラーの成分粒子間の相互作用に対するｐＨの影響

The interaction affecting the surface charge of constituent particles in coating color was studied through electrophoresis measurement and scanning electron microscopy (SEM) with the technique of osmium tetroxide fixation of latex.The pH dependence of aggregation state of amphoteric latex, which has both anionic and cationic groups, was visualized by SEM. Charge reversal of amphoteric latex and satin white by pH control affects significantly the dispersion state and electrokinetic properties of coating color. The transition pH for the dispersion state of amphoteric latex was ca. 7.1, showing some inconsistency with the electrophoretic behavior, which seemed to result from the relative strengths of electrostatic repulsion and Van der Waals attraction between latex particles. In the three-component system consisting of amphoteric latex/anionic latex/clay, the amphoteric latex mediates the binding between anionic latex and clay. This phenomenon might be useful in preventing the binder migration in actual coating procedures.The pH of charge reversal of satin white was ca. 7.5 as determined by electrophoresis. The coagulation behavior of latex particles onto satin white, as observed by SEM, clearly showed the role of this charge reversal : both types of latices were more uniformly distributed under alkaline conditions than under acidic conditions. In the latter condition, however, the difference between the two latices was not remarkable as expected.

Preparation, characterization, and albumin adsorption of amphoteric polymer latices

Amphoteric polymer latices were prepared by Hofmann reaction of styrene/ acrylamide (AAm) copolymer (P(St/AAm)) latex, i.e. by treating P(St/AAm) latex with sodium hypochlorite (NaOCl) and sodium hydroxide (NaOH) solutions. The reaction was carried out under different conditions to obtain latices having various isoelectric points (i.e.p.). All the latices obtained were highly monodisperse and of similar particle size. Conductometric titrations of amphoteric latices revealed that both acidic and basic groups existed on their surfaces, and that the surfaces of amphoteric latices were more hydrophilic than those of P(St/AAm) latex. The adsorption of bovine serum albumin (BSA) onto the latices was also studied. The adsorption of BSA onto amphoteric latices was lower than that onto P(St/AAm) latex, and was governed by electrostatic interactions. At lower ionic strengths, the adsorption behavior of BSA onto the amphoteric (H) latex having the highest i.e.p. was different from that onto other latices, showing maximum adsorption at a higher pH than the i.e.p. of the protein.

コーティングカラーの流動特性に関する研究 （第１報） バインダーラテックスの界面および粘弾性特性

The viscoelastic properties of binder latices for paper coating were investigated, together with dynamic viscoelastic properties of latex films and electron micrographs of latices, under various conditions. The amphoteric latex, binder-pigment latex and anionic latex were used in this work. The amphoteric latex has both anionic and cationic functional groups on its surface. The binder-pigment latex with a core-shell structure has dual functions : plastic pigment and binder.The low-shear and high-shear viscoelasticity of binder latices and clay slurry were measured with Brookfield viscometer and Hercules high-shear viscometer, respectively.At low-shear rates, the viscosity decreased with increasing particle size of latex. However, at high-shear rates, the different results were observed.On the amphoteric latex surface, the carboxyl groups are assumed to be fully dissociated over the region of pH 9-12, but the density of negative groups seems to increase because of the gradual decrease in the degree of dissociation of amino groups. Since the apparent particle size of latex increases with surface charge, the electroviscous effect, i. e. increase in viscosity by surface charge, can be observed. On the anionic latex surface, the charge density is assumed to be nearly constant above pH 8. However, below pH 8 the coagulation of particles could be observed probably because of the decrease in charge density.The time-dependent phenomena could not be observed at low-shear rate. However at high-shear rate, thixotropic properties of flow, and the internal structural breakdown of flow could be observed from time-dependent phenomena.

コーティングカラーの流動特性に関する研究 第２報 電顕写真の観察から見たコーティングカラーの静電的相互作用

For the purpose of visualizing the interaction between latex and pigment particles by electron microscopy, a new fixation technique was introduced that can preserve the shape of latex particles during the drying process. The method consists of mounting a drop of highly diluted coating color on a Formvar-coated copper grid for transmission electron microscopy (TEM) and treating the solution on the grid with osmium tetroxide vapor in a dessicator. Metal coating of this grid provided a specimen suited for scanning electron microscopy (SEM).When the pH of sample suspension was adjusted by using phosphate buffer, the SEM observation revealed a striking difference in behavior between a conventional anionic latex and an amphoteric latex in aggregating tendencies with clay particles. While the anionic latex particles were dispersed nearly uniformly on the substrate at both acidic and alkaline conditions, the amphoteric latex particles were strongly adsorbed onto clay particles in acidic and nearly neutral conditions. These results suggest the effectiveness of using amphoteric latexes as a means to control the latex-pigment interaction in coating colors for improving flow properties and preventing binder migration.The pH dependences of viscosity and the sediment volume ratio of undiluted coating colors were consistent with the latex-clay interaction as indicated by SEM observation.

The dielectric response of polystyrene latexes: Effects of alterations in the structure of the particle surface

The presence of a “hairy” layer has been hypothesized to explain discrepancies between the electrokinetic theory and experiments with polystyrene latexes by Van der Put and Bijsterbosch ( J. Colloid Interface Sci. 92, 499 (1983)]. We tested the hypothesis by making electrokinetic measurements on latexes before and after they had been heated above the polystyrene glass transition temperature. This sort of treatment may smooth the particle surface by collapsing or removing the charged polymer filaments which comprise the layer. Low-frequency dielectric measurements reveal that heat treatment improves the agreement between experiment and theory. For an amphoteric latex, the dielectric constant and conductivity decrease with heat-treatment time, and the characteristic relaxation frequency increases. This is consistent with the hairy surface hypothesis, suggesting that heat treatment smooths the surface, creating particles which more closely conform to the assumptions of the classical theory. Experiments with an anionic latex further suggest the presence of surface structure, but discrepancies between experiment and theory persist; it appears that factors other than hairiness contribute to these discrepancies. The suspension's dielectric properties are evidently very sensitive to the state of the particle surface, and thus dielectric spectroscopy offers a promising means of studying the structure of colloidal interfaces.

A new reference sample for microelectrophoresis

Syntheses of a reference particle dispersion stabilized sterically in an aqueous medium without any electrostatic effects and measurements of the zeta (ζ)-potential using the reference dispersion as a standard were performed under various experimental conditions. It became apparent that the dense adsorption layer of hydroxyl propyl cellulose (HPC), with a lower critical solution temperature (LCST), formed on latex particles with a low surface charge density ( σ 0 < 1 μC cm 2 ) at temperatures higher (60–80°C) than the LCST, plays a role in completely shielding the electrostatic effect arising from the surface charge on the bare particles. There was a critical amount of HPC adsorption above which the ζ-potential of the HPC-coated particles becomes really zero. Such reference particles with zero ζ-potential allow us to determine the electrophoretic mobility of unknown samples at the one-half depth in the electrophoretic cell by subtracting the mobility of the reference sample at the same level. Also, the ζ-potential of the cell wall can be easily determined from the mobility of the reference sample, because the apparent velocity profile of the reference sample indicates the liquid flow velocity profile in the cell. Determination of the ζ-potential for amphoteric latices and Agl sol using this new procedure indicates that the reference dispersion prepared here can be applied widely for many colloid particles dispersed in media of a wide range of pH and salt concentrations. Furthermore, the stability of the reference particles has been manifested in a few specific examples.

Dielectric spectroscopy of colloidal suspensions: I. The dielectric spectrometer

Four-electrode signal-processing techniques have a number of advantages over conventional bridge techniques in dielectric spectroscopy, but are not widely used because complex electronic circuits are required. A new design for a dielectric spectrometer of this type which circumvents these problems is described here. The device has been tested using electrical networks, pure electrolytes, and dilute colloidal suspensions. In experiments with a dilute, amphoteric latex, large suspension dielectric constants are found.