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.     

Particle interactions in kaolinite suspensions and corresponding aggregate structures

The surface charge densities of the silica face surface and the alumina face surface of kaolinite particles, recently determined from surface force measurements using atomic force microscopy, show a distinct dependence on the pH of the system. The silica face was found to be negatively charged at pH>4, whereas the alumina face surface was found to be positively charged at pH<6, and negatively charged at pH>8. The surface charge densities of the silica face and the alumina face were utilized in this study to determine the interaction energies between different surfaces of kaolinite particles. Results indicate that the silica face-alumina face interaction is dominant for kaolinite particle aggregation at low pH. This face-face association increases the stacking of kaolinite layers, and thereby promotes the edge-face (edge-silica face and edge-alumina face) and face-face (silica face-alumina face) associations with increasing pH, and hence the maximum shear-yield stress at pH 5-5.5. With further increase in pH, the face-face and edge-face association decreases due to increasing surface charge density on the silica face and the edge surfaces, and decreasing surface charge density on the alumina face. At high pH, all kaolinite surfaces become negatively charged, kaolinite particles are dispersed, and the suspension is stabilized. The face-face association at low pH has been confirmed from cryo-SEM images of kaolinite aggregates taken from suspension which show that the particles are mostly organized in a face-face and edge-face manner. At higher pH conditions, the cryo-SEM images of the kaolinite aggregates reveal a lower degree of consolidation and the edge-edge association is evident.     

Role of Electrostatic Repulsion on the Viscosity of Bidisperse Silica Suspensions

The flow behavior of bidisperse aqueous silica suspensions has been studied at different electrolyte concentrations as a function of shear rate, total volume fraction of the particles, and volume ratio of small to large particles. It is shown that the range of the electrostatic repulsion plays an important role in determining the viscosity of the suspension. Binary mixtures of particles of longer range repulsive forces showed higher viscosities than the suspensions of shorter range electrostatic interactions. Bimodal suspensions of long-range interactions showed non-Newtonian behavior over wider ranges of shear due to the deformation of the ionic cloud around the particles, which is larger in these systems. The viscosity of bimodal suspensions used in this study was scaled with respect to the viscosity of the related monosized systems and the viscosity of one bimodal suspension at a fixed total volume fraction of the particles, employing our earlier scaling method. The model normalizes the effect of colloidal forces by introducing a scaling factor that collapses the data into a single curve for bimodal suspensions of a particular size ratio, and it is shown that the model is valid for systems with both short-range and long-range repulsive forces. Copyright 1999 Academic Press.     

Micro-structure differences in kaolinite suspensions

SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different micro-structure constitution. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge-to-face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained.     

Advantages and limitations of the synchrotron based transmission X-ray microscopy in the study of the clay aggregate structure in aqueous suspensions

This paper reports new application of new transmission X-ray microscopy powered by a synchrotron source for the study of aqueous based clay suspensions. This paper delineates the advantages and limitations of this method. The tested transmission X-ray microscopy (TXM) technique has shown good agreement with the cryo-stage SEM technique. The spacial resolution of this TXM technique is 60 nm and clay particles with diameter below 500 nm are clearly visible and their pseudohexagonal symmetry is recognizable in detail. It is clearly demonstrated the methodology of implementing TXM to study aqueous based clay suspensions that are close to approximately 60 nm tomographic resolution. The technique enables us to study discrete structure of clay suspensions in water and within aggregates. This has never been previously possible. Larger crystals, more compact aggregates and less colloidal fraction present in kaolinite from Georgia has impact on faster settling and gelling in denser suspension than for Birdwood kaolinite in which colloidal particles create gel-like networking in less dense aqueous suspension.     

Influence of solution composition and ultrasonic treatment on optical spectra of TiO2 aqueous suspensions

Investigation of TiO(2) aqueous suspensions has shown that their optical spectra can be unstable, with instability not related to precipitation or adherence of TiO(2) particles to the vessel walls. Increase of ionic strength of the suspension as well as neutralization of charged TiO(2) particles via pH adjustment accelerates the optical density drop. Vice versa, increasing the charge of TiO(2) particles via shifting pH in acidic or basic directions stabilizes the suspension's optical spectra, and ultrasonic treatment promotes optical density recovery. The observed behavior is attributed to alteration in the size of the suspension aggregates.     

Influence of sodium chloride,carbonates, and iron hydroxides on the viscosity of aqueous suspensions of clay minerals

The influence of sodium chloride solutions containing carbon dioxide on the viscosity of a maximally destroyed structure of suspensions of hydromica, kaolinite, natural iron-containing polymineral carbonate clay, iron oxides, and freshly prepared and dried montmorillonite is studied. The effect of physicochemical transformations of finely dispersed carbonates on the surface structure of a dispersed phase in suspensions of clay and iron oxide particles is considered. On the basis of the obtained results, a colloidochemical model for the destruction of ground barriers of storage ponds for mineralized water under the conditions of catastrophic phenomena is specified.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 32–37.Original Russian Text Copyright © 2005 by Kovzun, Kovalenko, Protsenko.     

Kinetics of adsorption of high molecular weight anionic polyacrylamide onto kaolinite: the flocculation process

The adsorption kinetics of anionic polyacrylamide flocculant onto kaolinite clay are examined as a function of flocculant dosage and pH. Special attention has been given to the flocculation effect during the adsorption process and the resulting inhibition of further adsorption. At pH 8.5 the adsorption capacity of anionic polyacrylamide on kaolinite is low while at pH 4.5, the adsorption capacity increases. Flocculant adsorption has been shown to be related to the amount of available surface area, pH, flocculant dosage, and the resulting floc strength, which controls the rate of new surface area exposure and hence the continuation of further adsorption. At both pH 4.5 and pH 8.5, complete adsorption is achieved at low flocculant dosages and adsorption equilibrium is achieved at high flocculant dosages after 1 day. In contrast, at intermediate flocculant dosages adsorption equilibrium is not reached over a 7-day period, due to a continuously increasing surface area.     

N-(2-氨乙基)-月桂酰胺浮选铝硅酸盐矿物的研究

研究了N (2 氨乙基) 月桂酰胺对高岭石、伊利石和叶腊石等铝硅酸盐矿物的浮选行为.发现该表面活性剂对叶腊石的浮选回收率最高可达97.7％，对伊利石和高岭石的回收率相对较低，一般不超过82％.矿浆pH对高岭石、伊利石和叶腊石的回收率影响较小.酸性矿浆中表面活性剂通过静电引力吸附在矿粒表面；碱性矿浆中，表面活性剂通过氢键吸附在矿粒表面.红外吸收光谱证明，三种矿物表面中均存在－OH；在一个较宽的pH范围内，三种矿物矿浆的Zeta电位均为负值，表明矿粒表面荷负电.矿粒的扫描电镜（SEM）照片（×15000）表明，叶腊石主要呈薄片状颗粒，高岭石和伊利石颗粒呈不规则形状.     

Mechanism of structural ordering of monodisperse spherical silica particles in concentrated alcohol suspensions

Structural ordering of monodispersed spherical silica particles (MSSP) occurs in ammonia stabilized concentrated suspensions obtained by tetraethoxysilane (TEOS) hydrolysis in alcohol-aqueous solutions in the ammonia concentration range from 0.0001 to 0.0008 mol/L. MSSP interaction follows the DLFO (Deryagin, Landau, Ferway, and Overbeck) mechanism when electrostatic repulsive forces between the particles predominate, and the structural ordering requires straightened conditions, which are provided by suspension concentrating through MSSP gravitational precipitation.     

Effect of pH and Salt on Rheological Properties of Aerosil Suspensions

Ionic strength and pH will influence the zeta potential of suspended particles, and consequently particle interactions and rheological properties as well. In this study the rheological properties and aggregation behaviour of Aerosil particles dispersed in aqueous solutions with various pH and salt concentration were studied. The potential energy was estimated by the DLVO theory and short range hydration forces and compared to the experimentally determined zeta potential. The strongest attraction between particles occurs at the isoelectric point (pH 4) and resulted in large aggregates, which gave relatively higher values of viscosity, yield stress, moduli, and shear thinning effects. The relative viscosity as a function of volume fraction was fitted to the Krieger and Dougherty model for all the suspensions. Oscillation measurements showed that the suspensions display elastic behaviour at low pH and viscous behavior at high pH. Furthermore, suspensions with high salt content had higher storage moduli. A power law dependency of storage moduli with volume fraction could be used to indicate the interaction strength between particles.     

Colloid stability of thymine-functionalized gold nanoparticles

Gold nanoparticles surface-coated with thyminethiol derivatives containing long hydrocarbon chains have been prepared. The diameter of the particles is 2.2 and 7.0 nm, respectively, with a relatively narrow size distribution. Thyminethiol derivatives are attached to the gold particle surfaces with thymine moieties as the end groups. The colloid stability of the gold nanoparticles as a function of the type and concentration of monovalent salt, pH, and particle size was investigated in alkaline, aqueous solutions. The gold particles are stable in concentrated NaCl and KCl solutions, but are unstable in concentrated LiCl and CsCl solutions. The larger gold particles are more sensitive to salt concentration and aggregate at lower salt concentrations. The reversible aggregation and dispersion of the gold particles can be controlled by changing the solution pH. The larger gold particles can be dispersed at higher pH and aggregate faster than the smaller particles, due to stronger van der Waals forces between the larger particles. Hydration forces play an important role in stabilizing the particles under conditions where electrostatic forces are negligible. The coagulation of the gold nanoparticles is attributed to van der Waals attraction and reduced hydration repulsion in the presence of LiCl and CsCl.     

Kinetics of sodium dodecyl benzene sulfonate adsorption on hematite and its interaction with polyacrylamide

This article describes the adsorption of sodium dodecyl benzene sulfonate, an anionic surfactant, on a hematite surface and that when the surface is preadsorbed with polyacrylamide. The adsorption of surfactant on a hematite surface has been studied through equilibration and during kinetics measurements at three pH levels, viz. 4.0, 7.0, 8.9. The surfactant adsorbs strongly on the hematite surface. The adsorption density at equilibrium as well as the rate of adsorption are dependent on the suspension pH. The maximum adsorption density has been observed at pH 4, which reflects strong adsorption of negatively charged sulfonate ions on the oppositely charged Fe₂O₃ surface (point of zero charge, 6.4). The adsorption density reaches its equilibrium value sooner in the case of an alkaline suspension and later in the case of acidic pH. The polymer surfactant interaction has been noticed in the present study and is also a function of pH. The hematite mineral when preadsorbed with the polymer draws fewer of the surfactant molecules at lower surface coverage (during the initial period of the kinetics measurement) irrespective of the pH. When the adsorption of the surfactant reaches a value which is near the equilibrium one, the pH effect is evident. In the case of acidic pH, the surfactant adsorbs more on the hematite surface when preadsorbed with the polymer compared to the bare surface. In the case of neutral or alkaline pH, however, the density of surfactant adsorption remains lower throughout the kinetics measurement when the surface is preadsorbed with the flocculant compared to the bare surface. The particles also remain flocculated till the end of the experiment, whereas at pH 4 the particles are deflocculated. In addition to pH, the electrostatic nature of the adsorbent and the presence of anionic surfactant have an influence on the flocculation–deflocculation phenomena. The polymer–surfactant interaction has been schematically represented. The surfactant is bound with polymeric chains as a combination of its monomeric form as well as in the form of association in the case of acidic media and in competition with polymer in the case of alkaline media. Received: 18 April 2000/Accepted: 2 August 2000     

表面活性剂和聚乙烯吡咯烷酮在ZrO2上的吸附对其悬浮体稳定性的影响

研究了水溶液中十二烷基苯磺酸钠（ＳＤＢＳ）、溴代十四烷基吡啶（ＴＰＢ）和聚乙烯吡咯烷酮（ＰＶＰ）在ＺｒＯ２上的吸附及对ＺｒＯ２水悬浮体稳定性的影响。结果表明：ｐＨ＝２．４时ＳＤＢＳ在ＺｒＯ２上的吸附等湿线为ＬＳ型，ｐＨ＝７．０时ＴＰＢ的吸附等温线为Ｓ型，吸附等温线与ＺｒＯ２粒子ζ电势变化同线有大体一致的关系。在最大吸附量时ＺｒＯ２粒子ζ电势较大，且吸附的表面活性剂离子形成大部分亲水基朝向水相的表面     

Thixotropic properties of aqueous suspensions containing cationic starch and aluminum magnesium hydrotalcite-like compound

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio (R) of HTlc to CS, the equilibrium viscosity (eta(eq)) and the consistency coefficient (m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the eta(eq) and m values of the suspensions in the R range of 0-0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41+/-0.25. The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R=0.08 in the pH range of 7.66-9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex (R=0.02), into positive thixotropy (R=0.05 and 0.08) with the increase of R in the studied R range of 0-0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.     

Surface chemistry and rheology of polysulfobetaine-coated silica

We have measured the viscosity of suspensions of colloidal silica particles (d = 300 nm) and the properties of silica surfaces in solutions of a polymer consisting of zwitterionic monomer groups, poly(sulfobetaine methacrylate), polySBMA. This polymer has potential use in modifying surface properties because the polymer is net uncharged and therefore does not generate double-layer forces. The solubility of the polymer can be controlled and varies from poor to good by the addition of sodium chloride salt. Ellipsometry was used to demonstrate that polySBMA adsorbs to silica and exhibits an increase in surface excess at lower salt concentration, which is consistent with a smaller area per molecule at low salt concentration. Neutron reflectivity measurements show that the adsorbed polymer has a thickness of about 3.7 nm and is highly hydrated. The polymer can be used to exercise considerable control over suspension rheology. When silica particles are not completely covered in polymer, the suspension produces a highly viscous gel. Atomic force microscopy was used to show this is caused by bridging of polymer between the particles. At higher surface coverage, the polymer can produce either a high or very low viscosity slurry depending on the sodium chloride concentration. At high salt concentration, the suspension is stable, and the viscosity is lower. This is probably because the entrainment of many small ions renders the polymer film highly hydrophilic, producing repulsive surface forces and lubricating the flow of particles. At low salt concentrations, the polymer is barely soluble and more densely adsorbed. This produces less stable and more viscous solutions, which we attribute to attractive interactions between the adsorbed polymer layers.     

Untypical rheological behaviour of the lignite–carboxymethylcellulose–water dispersion system

Suspensions of lignite in a solution of a high molecular weight carboxymethylcellulose show peculiar rheological behaviour. Unless the lignite concentration is sufficiently high, apparent viscosity and viscoelastic moduli of the suspension are lower than those of the pure solution. This effect is not suppressed by changing pH and seems to be common for low-concentrated suspensions in solutions of high molecular weight (bio)polymer. It is explained by specific structuring of the suspensions. Lignite particles at lower concentration separate long cellulose chains and facilitate their movement under shear flow. The particles loosen inter-chain contacts, disturb and release elastic gel-like structure formed by the long cellulose chains, which results in the low strain oscillatory deformation, the decrease in the moduli and the increase in the loss angle. If the amount of lignite particles is sufficiently high, suspension stiffening occurs as usual. No such effect was observed for suspensions prepared from the low molecular weight derivative. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Primary electroviscous effect in a moderately concentrated suspension of charged spherical colloidal particles

On the basis of the standard theory of the primary electroviscous effect in a moderately concentrated suspension of charged spherical particles in an electrolyte solution presented by Ruiz-Reina et al. (Ruiz-Reina, E.; Carrique, F.; Rubio-Hernández, F. J.; Gómez-Merino, A. I.; García-Sánchez, P. J. Phys. Chem. B 2003, 107, 9528), which is applicable for the case where overlapping of the electrical double layers of adjacent particles can be neglected, the general expression for the effective viscosity or the primary electroviscous coefficient p of the suspension is derived. This expression is applicable for a suspension of spherical particles of radius a carrying arbitrary zeta potentials zeta at the particle volume fraction phi < or = 0.3 for the case of nonoverlapping double layers, that is, at kappaalpha > 10 (where kappa is the Debye-Hückel parameter). A simple approximate analytic expression for p applicable for particles with large kappaalpha and arbitrary zeta is presented. The obtained viscosity expression is a good approximation for moderately concentrated suspensions of the particle volume fraction phi < or = 0.3, where the relative error is negligible for kappaalpha > or =100 and even at kappaalpha = 50 the maximum error is approximately 20%. It is shown that a maximum of p, which appears when plotted as a function of the particle zeta potential, is due to the relaxation effect as in the case of the electrophoresis problem.     

Polydisperse fractal aggregate formation in clay mineral and iron oxide suspensions, pH and ionic strength dependence

pH- and ionic-strength-dependent aggregation of permanently and conditionally charged clay mineral (montmorillonite) and iron oxide (magnetite) particles was investigated by means of dynamic light scattering and rheology. An indifferent electrolyte (NaCl) was used. The surface charging of solids was determined by acid–base titration. The point of zero charge (PZC) of magnetite seemed to be at pH 8.0 ± 0.1. The permanent negative charges on the basal plane of montmorillonite influence the interfacial distribution of H⁺ and Na⁺ ions. The pH dependence of the electrophoretic mobility showed directly the dominance of negative charges on montmorillonite lamellae independently of pH, while for magnetite the sign of the mobility reversed at pH ˜ 8.0. Montmorillonite particles formed stable suspensions; coagulation did not take place below 35 mM 1:1 electrolyte independently of pH. The aggregation of magnetite sol becomes significant near the pH of the PZC even at low ionic strength. Colloidal stability in composite systems was investigated at pH ˜ 4, where oxide and clay mineral particles are oppositely charged. At the lowest NaCl concentrations (1, 5 mM) the mixed systems remained stable and aggregation of oppositely charged particles could not be observed at all. Heterocoagulation of dissimilar particles needed a definite amount of dissolved electrolytes (about 8 mM). Mixed clay mineral and oxide systems are more sensitive to electrolyte under acidic conditions than those separately. Rheological investigation of the mixed clay mineral–oxide suspensions at pH ˜ 4 provided proof for the absence of attractive particle interaction at low ionic strength (2 mM). A physical network of oppositely charged particles could form only at higher salt concentration, for example, in the presence of 10 mM NaCl. The yield value of plastic systems showed a significant maximum at 1:15 magnetite/montmorillonite mass ratio. Received: 21 November 2000 Accepted: 20 December 2000     

Peculiarities of the formation of polyacrylamide compound-based polyelectrolyte complexes in the course of the flocculation of clay-salt dispersions

Peculiarities of the formation of polyelectrolyte complexes based on cationic and anionic copolymers of acrylamide having different macromolecule charge densities on the surfaces of kaolin particles in highly concentrated salt solution are investigated. The interactions of the copolymers with the clay particle surface and with each other are studied by electrokinetic and IR spectroscopy methods. The rheological properties of kaolin suspensions are investigated in a salt solution in the presence of the polyelectrolytes. The flocculation ability of the polyelectrolytes and their binary mixtures with respect to clay-salt dispersion is estimated. The mechanism for the formation of polyelectrolyte complexes on the surface of clay particles is discussed. It is shown that the complexation of oppositely charged polyelectrolytes on the surfaces of clay particles intensifies the flocculation of clay-salt dispersions.