The Dispersion Properties of Precipitated Calcium Carbonate Suspensions Adsorbed with Alkyl Polyglycoside in Aqueous Medium

The zeta potentials and dispersion properties of precipitated calcium carbonate suspensions adsorbed with alkyl polyglycosides in aqueous medium were investigated. Within the investigated pH ranges, the adsorption curves of alkyl polyglycosides on calcium carbonates show sigmoidal shapes, and the zeta potential decreases as the amount of adsorption increases. At positively charged surfaces of low pH, the adsorption amounts were greater than those at negatively charged surfaces, indicating that alkyl polyglycosides were negatively charged in aqueous solutions. At low concentrations of alkyl polyglycosides, the dispersion stabilities of suspensions were very poor and showed no linearity with zeta potentials over the entire range of pHs, which may be attributed to the onset of hydrophobic interaction between particles due to the adsorption of surfactant molecules. This destabilization continued until monolayer coverage by the surfactant layer was complete. Based on the classical DLVO theory, there may be a strong hydrophobic interaction between particles. Beyond monolayer adsorption, the dispersion stability increases, probably by the formation of hemimicelle or admicelle. Therefore, it is believed that ionization of alkyl polyglycosides and admicelles of surfactants on particle surface plays a key role in the stability of dispersions and the abrupt increase in adsorption. Copyright 2000 Academic Press.     

Synergistic stabilization of emulsions by a mixture of surface-active nanoparticles and surfactant

The stability and rheology of tricaprylin oil-in-water emulsions containing a mixture of surface-active hydrophilic silica nanoparticles and pure nonionic surfactant molecules are reported and compared with those of emulsions stabilized by each emulsifier alone. The importance of the preparation protocol is highlighted. Addition of particles to a surfactant-stabilized emulsion results in the appearance of a small population of large drops due to coalescence, possibly by bridging of adsorbed particles. Addition of surfactant to a particle-stabilized emulsion surprisingly led to increased coalescence too, although the resistance to creaming increased mainly due to an increase in viscosity. Simultaneous emulsification of particles and surfactant led to synergistic stabilization at intermediate concentrations of surfactant; emulsions completely stable to both creaming and coalescence exist at low overall emulsifier concentration. Using the adsorption isotherm of surfactant on particles and the viscosity and optical density of aqueous particle dispersions, we show that the most stable emulsions are formed from dispersions of flocculated, partially hydrophobic particles. From equilibrium contact angle and oil-water interfacial tension measurements, the calculated free energy of adsorption E of a silica particle to the oil-water interface passes through a maximum with respect to surfactant concentration, in line with the emulsion stability optimum. This results from a competition between the influence of particle hydrophobicity and interfacial tension on the magnitude of E.     

Effect of dispersion pH on the formation and stability of Pickering emulsions stabilized by layered double hydroxides particles

Using positively charged plate-like layered double hydroxides (LDHs) particles as emulsifier, liquid paraffin-in-water emulsions stabilized solely by such particles are successfully prepared. The effects of the pH of LDHs aqueous dispersions on the formation and stability of the emulsions are investigated here. The properties of the LDHs dispersions at different pHs are described, including particle zeta potential, particle aggregation, particle contact angle, flow behavior of the dispersions and particle adsorption at a planar oil/water interface. The zeta potential decreases with increasing pH, leading to the aggregation of LDHs particles into large flocs. The structural strength of LDHs dispersions is enhanced by increasing pH and particle concentration. The three-phase contact angle of LDHs also increases with increasing pH, but the variation is very small. Visual observation and SEM images of the interfacial particle layers show that the adsorption behavior of LDHs particles at the planar oil/water interface is controlled by dispersion pH. We consider that the particle-particle (at the interface) and particle-interface electrostatic interactions are well controlled by adjusting the dispersion pH, leading to pH-tailored colloid adsorption. The formation of an adsorbed particle layer around the oil drops is crucial for the formation and stability of the emulsions. Emulsion stability improves with increasing pH and particle concentration because more particles are available to be adsorbed at the oil/water interface. The structural strength of LDHs dispersions and the gel-like structure of emulsions also influence the stability of the emulsions, but they are not necessary for the formation of emulsions. The emulsions cannot be demulsified by adjusting emulsion pH due to the irreversible adsorption of LDHs particles at the oil/water interface. TEM images of the emulsion drops show that a thick particle layer forms around the oil drops, confirming that Pickering emulsions are stabilized by the adsorbed particle layers. The thick adsorbed particle layer may be composed of a stable inner particle layer which is in direct contact with the oil phase and a relatively unstable outer particle layer surrounding the inner layer.     

Small-angle neutron scattering studies of an adsorbed non-ionic surfactant (C12E24) on hydrophobised silica particles in water

Small-angle neutron scattering (SANS) studies of aqueous dispersions of St?ber silica particles (which have been hydrophobised by having 1-octadecanol grafted to their surface), carrying an adsorbed layer of the nonionic surfactant C12E24, in water, have been performed as a function of temperature. Using mixtures of D2O and H2O, the composition of the continuous phase was adjusted to have the same scattering length density as the silica particles. Hence, only the scattering from the 1-octadecanol and C12E24 layers was detected. The data have been analyzed using both a surface Guinier analysis and a two-layer structure model. It has been found that a step profile best describes the inner combined adsorbed layer (1-octadecanol grafted chains, plus the penetrating alkyl chains from the surfactant) and a semi-Gaussian profile the extended poly(ethylene oxide) outer layer. Both analyses demonstrated that the combined surface layer contracted with increasing temperature.     

Depletion flocculation of latex dispersion in ionic micellar systems

The flocculation behavior of anionic and cationic latex dispersions induced by addition of ionic surfactants with different polarities (SDS and cetyltrimethylammonium bromide (CTAB)) have been evaluated by rheological measurements. It was found that in identical polar surfactant systems with particle surfaces of SDS + anionic lattices and CTAB + cationic lattices, a weak and reversible flocculation has been observed in a limited concentration region of surfactant, which was analyzed as a repletion flocculation induced by the volume-restriction effect of the surfactant micelles. On the other hand, in oppositely charged surfactant systems (SDS + cationic lattices and CTAB + anionic lattices), the particles were flocculated strongly in a low surfactant concentration region, which will be based on the charge neutralization and hydrophobic effects from the adsorbed surfactant molecules. After the particles stabilized by the electrostatic repulsion of adsorbed surfactant layers, the system viscosity shows a weak maximum again in a limited concentration region. This weak maximum was influenced by the shear rate and has a complete reversible character, which means that this weak flocculation will be due to the depletion effect from the free micelles after saturated adsorption.     

Stability of silicon and titanium carbide suspensions in electrolyte, poly(ethylene oxide), and PEO-surfactant solutions

It has been shown that the coagulation values of counterions for SiC and TiC suspensions with particle radius from 0.5 to 5 microm obey a z(2.5-3.5) law and there is an insufficient change in the critical concentration of 1-1 electrolytes (CCE) when the surface potential of particles increases more than two times. Also, the CCE values hardly depend on the position of counterions in the lyotropic sequence. This is explained by aggregation of SiC and TiC particles at a secondary minimum, which is proved by calculations of the potential curves of interparticle interactions using the DLVO theory. The adsorption of poly(ethylene oxide) on the surfaces studied does not cause--in contradiction to dispersions with smaller particles--an unlimited growth in the stability of suspensions. This is due to the aggregation of large particles with adsorbed PEO, as in polymer-free dispersions, under barrierless conditions in which the coordinates of the secondary minimum are determined by superposition of molecular attractive forces and steric repulsive forces of adsorbed polymeric chains, without a contribution from the electric repulsion term. PEO-anionic surfactant complexes possess higher stabilizing capacity compared to the individual components of the mixture. Our results show that the adsorbed polymer layers may hinder the aggregation both in the primary and in the secondary minimum for not very large particles only, the critical size of which depends on the dispersed phase nature and the molecular mass of the polymer.     

Homogeneous functional Ni-P/ceramic nanocomposite coatings via stable dispersions in electroless nickel electrolytes

Stable nanoparticle dispersions in concentrated electrolytes are prerequisite for a variety of advanced nanocomposites prepared by deposition techniques. In this work we investigate the synthesis of electroless Ni-P/functional ceramic coatings from concentrated electrolytes containing functional nanoparticles such as TiO(2), α-Fe(2)O(3), ITO, and CeO(2). Stable nanoparticle dispersions in both low and high phosphorus electrolytes are achieved at plating temperatures (80-90 °C) by a generalized scheme employing comb-polyelectrolyte and antifreeze additives. Dispersion stability at room temperature is achieved in both low and high phosphorus EN media using anionic comb-polyelectrolyte surfactants with polyether side chain of 1100 g/mol. The optimal surfactant concentration is determined by zeta-potential and thermo-gravimetric analysis. Without additives the dispersions flocculate and sediment between 65 and 80 °C. Such phenomenon is believed to be associated with a critical flocculation temperature (CFT). The CFT is also weekly dependent on the particle type and the high ionic strength media. Addition of antifreeze additives such as propylene glycol and urea to the dispersions restores stability and increase the CFT for all particles. We estimate an average increase of the CFT by 1.5-2 °C per 1% additive for all particles and electrolytes. While the particle stabilization scheme is generalized in this work, the composite EN plating proved highly dependent on particle type. Baths containing ITO nanoparticles showed no plating reactions and those containing α-Fe(2)O(3) no nanoparticle co-deposition. In contrast, homogeneous Ni-P/TiO(2) and Ni-P/CeO(2) nanocomposites with up to 22 vol.% nanoparticles are produced. The possible application of the stabilization principles developed here for other functional nanocomposite systems is discussed.     

CORRELATION OF DISPERSION STABILITY WITH SURFACTANT CONCENTRATION AND ABRASIVE PARTICLE SIZE FOR CHEMICAL MECHANICAL POLISHING (CMP) SLURRIES

The preparation of stable colloidal slurries is often difficult in industries where many chemical components are added into the slurries. A critically acclaimed example of such an industry is the chemical mechanical polishing (CMP) industry which involves polishing slurries with several chemical additives. In the present work, the stabilization of a slurry used for CMP of metals is investigated in detail. This high ionic strength slurry has been stabilized using an optimaJ combination of sodium dodecyl sulfate (anionic surfactant) and Tween 80 (nonionic surfactant). The amount of surfactant needed to impart stability has been investigated in this study for two different sizes of abrasive particles. It has been found that the amount of surfactant needed to stabilize the slurry increases as the total surface area per gram of panicles increases. Slurry stabilization has been correlated with particle size measurements. It has been found that the average panicle size of the slurry decreases as the stability of the slurry increases. Stable slurries have been found to have particle sizes close to those of the particles before agglomeration. It is proposed that the stabilized CMP slurries can lead to reduced defects in wafers by preventing agglomeration of panicles.     

Effect of surfactants on shear-induced gelation and gel morphology of soft strawberry-like particles

The role of surfactant type in the aggregation and gelation of strawberry-like particles induced by intense shear without any electrolyte addition is investigated. The particles are composed of a rubbery core, partially covered by a plastic shell, and well stabilized by fixed (sulfate) charges in the end group of the polymer chains originating from the initiator. In the absence of any surfactant, after the system passes through a microchannel at a Peclet number equal to 220 and a particle volume fraction equal to 0.15, not only shear-induced gelation but also partial coalescence among the particles occurs. The same shear-induced aggregation/gelation process has been carried out in the presence of an ionic (sulfonate) surfactant or a nonionic (Tween 20) steric surfactant. It is found that for both surfactants shear-induced gelation does occur at low surfactant surface density but the conversion of the primary particles to the clusters constituting the gel decreases as the surfactant surface density increases. When the surfactant surface density increases above certain critical values, shear-induced gelation and eventually even aggregation do not occur any longer. For the sulfonate surfactant, this was explained in the literature by the non-DLVO, short-range repulsive hydration forces generated by the adsorbed surfactant layer. In this work, it is shown that the steric repulsion generated by the adsorbed Tween 20 layer can also protect particles from aggregation under intense shear. Moreover, the nonionic steric surfactant can also protect the strawberry-like particles from coalescence. This implies a decrease in the fractal dimension of the clusters constituting the gel from 2.76 to 2.45, which cannot be achieved using the ionic sulfonate surfactant.     

Viscoelastic properties of polystyrene and poly(methyl methacrylate) dispersions sterically stabilized by hydrophobically modified inulin (polyfructose) polymeric surfactant

Recently, steric repulsive forces induced by a new graft copolymer surfactant, which is based in inulin (polyfructose), have been described. Previous investigations by atomic force microscopy between solid surfaces covered with adsorbed surfactant indicated strong repulsive forces even at high electrolyte concentration, due to the steric repulsion produced by the surfactant hydration. In the present paper, the colloidal stabilization provided by this surfactant is studied by rheology. The measurements were carried out on sterically stabilized polystyrene (PS) and poly(methyl methacrylate) (PMMA) containing adsorbed surfactant (INUTEC SP1). Steady-state shear stress as a function of shear rate curves was established at various latex volume fractions. The viscosity volume fraction curves were compared with those calculated using the Doughtry-Krieger equation for hard sphere dispersions. From the experimental eta r-phi curves the effective volume fraction of the latex dispersions could be calculated and this was used to determine the adsorbed layer thickness Delta. The value obtained was 9.6 nm, which is in good agreement with that obtained using atomic force microscopy (AFM). Viscoelastic measurements of the various latex dispersions were carried out as a function of applied stress (to obtain the linear viscoelastic region) and frequency. The results showed a change from predominantly viscous to predominantly elastic response at a critical volume fraction (phi c). The effective critical volume fraction, phi eff, was calculated using the adsorbed layer thickness (Delta) obtained from steady-state measurements. For PS latex dispersions phi eff was found to be equal to 0.24 whereas for PMMA phi eff=0.12. These results indicated a much softer interaction between the latex dispersions containing hydrated polyfructose loops and tails when compared with latices containing poly(ethylene oxide) (PEO) layers. The difference could be attributed to the stronger hydration of the polyfructose loops and tails when compared with PEO. This clearly shows the much stronger steric interaction between particles stabilized using hydrophobically modified inulin.     

Liquid-liquid phase-transfer of magnetic nanoparticles in organic solvents

We report a novel route for the preparation of well-defined colloidal dispersions of magnetic nanoparticles stabilized by steric repulsion in organic solvents. The usual methods standardly lead to the surfaction of multiparticle aggregates, incompatible with our long-term aim of studying and modeling the influence of magnetic dipolar interactions in colloidal dispersions which are free of aggregates, all other interactions being perfectly defined. A new and reproducible method based on a surfactant-mediated liquid-liquid phase transfer of individually dispersed gamma-Fe(2)O(3) nanoparticles from an aqueous colloidal dispersion to an organic phase is developed. The choice of the reagent and the preparation techniques is discussed. Among several solvent/surfactant pairs, the cyclohexane/dimethyldidodecylammonium bromide (DDAB) system is found to fulfill the colloidal stability criterion: aggregation does not appear, even upon aging. A complete transfer of isolated particles is observed above a threshold in DDAB concentration. The nanoparticle surface is then fully covered with adsorbed DDAB molecules, each surfactant head occupying a surface of 0.57+/-0.05 nm(2). The volume fraction of the cyclohexane-based organosols is easily tunable up to a volume fraction of 12% by modifying the volume ratio of the organic and of the aqueous phases during the liquid-liquid phase transfer.     

Dispersion Stability Evaluated by Experimental Design

The stability of paraffin and hydrocarbon oil dispersions stabilized by nonionic surfactants has been systematically evaluated. Using experimental design, the influence of the following parameters on dispersion stability was studied: surfactant concentration, shear rate, shear time and temperature of homogenisation. The experiments were evaluated with respect to particle size and particle migration velocity by a scanning optical analysis technique. This scanning technique monitors physical variations in a dispersion as a function of time and the technique is well suited for evaluation of dispersion stability. It was found that the only factor examined affecting particle migration velocity in a significant way was the surfactant concentration. A pronounced maximum in creaming rate was obtained at around 10 wt% surfactant both for the paraffin dispersions (suspensions at room temperature) and for the hydrocarbon oil emulsions. This surfactant-induced instability is explained as depletion flocculation caused by elongated surfactant micelles or by small oil-containing aggregates formed as microemulsion droplets during the emulsification process.     

New protocols for preparing dipalmitoylphosphatidylcholine dispersions and controlling surface tension and competitive adsorption with albumin at the air/aqueous interface

The adsorption behavior of dipalmitoylphosphatidylcholine (DPPC), which is the major component of lung surfactant, at the air/aqueous interface and the competitive adsorption with bovine serum albumin (BSA) were studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. Dynamic surface tensions lower than 1 mN/m were observed for DPPC dispersions, with mostly vesicles, prepared with new protocols, involving extensive sonication above 50 °C. The lipid adsorbs faster and more extensively for DPPC dispersions with vesicles than with liposomes. For DPPC dispersions by a certain preparation procedure at T > T_c, when lipid particles were observed on the surface, dynamic surface tensions as low as 1 mN/m were measured. Moreover, IRRAS intensities and ellipsometric δΔ values were found to be much higher than the values for other DPPC dispersions or spread DPPC monolayers, suggesting that a larger amount of liposomes or vesicles adsorb on the surface. For DPPC/BSA mixtures, the tension behavior is controlled primarily by BSA, which prevents the formation of a dense DPPC monolayer. When BSA is injected into the subphase with a spread DPPC monolayer or into a DPPC dispersion with preadsorbed layers, little or no BSA adsorbs and the DPPC layer remains on the surface. When a DPPC monolayer is spread on a BSA solution at 0.1 wt% at 25 °C, then DPPC lipid can displace the adsorbed BSA molecules. The lack of BSA adsorption, and the expulsion of BSA by DPPC monolayer is probably due to the strong hydrophilicity of the lipid polar headgroup. When a DPPC dispersion is introduced with Trurnit's method or when dispersion drops are sprayed onto the surface of a DPPC/BSA mixture, the surface tension becomes lower and is controlled by DPPC, which can prevent the adsorption of BSA. The results may be important in understanding inhibition of lung surfactants by serum proteins and in designing efficient protocols of surfactant preparation and administration.     

Electrokinetic behavior and colloidal stability of polystyrene latex coated with ionic surfactants

This work is focused on analyzing the electrokinetic behavior and colloidal stability of latex dispersions having different amounts of adsorbed ionic surfactants. The effects of the surface charge sign and value, and the type of ionic surfactant were examined. The analysis of the electrophoretic mobility (mu(e)) versus the electrolyte concentration up to really high amounts of salt, much higher than in usual studies, supports the colloidal stability results. In addition, useful information to understand the adsorption isotherms was obtained by studying mu(e) versus the amount of the adsorbed surfactant. Aggregation studies were carried out using a low-angle light scattering technique. The critical coagulation concentrations (ccc) of the particles were obtained for different surfactant coverage. For latex particles covered by ionic surfactants, the electrostatic repulsion was, in general, the main contribution to the colloidal stability of the system; however, steric effects played an important role in some cases. For latices with not very high colloidal stability, the adsorption of ionic surfactants always improved the colloidal stability of the dispersion above certain coverage, independently of the sign of both, latex and surfactant charge. This was in agreement with higher mobility values. Several theoretical models have been applied to the electrophoretic mobility data in order to obtain different interfacial properties of the complexes (i.e., zeta potential and density charge of the surface charged layer).     

Stabilization of nanodiamond dispersions with nonionic surfactant Igepal CA-630 in water and dimethyl sulfoxide

Nanodiamond dispersions in water and DMSO were stabilized with adsorbed layers of nonionic surfactant Igepal CA-630. Adsorption isotherms of Igepal CA-630 onto nanodiamonds from water and DMSO reveal the structure of the adsorbed layers. The stabilized aqueous dispersions retain their resistance to aggregation for at least 7 days, while the dispersions in DMSO are stable for 3 days.     

Interfacial properties of emulsions stabilized with surfactant and nonsurfactant coated boehmite nanoparticles

The properties of emulsions stabilized with surface-modified boehmite particles of 26 and 8 nm in diameter have been investigated. The surface-modified particles were prepared by mixing aqueous dispersions of cationic boehmite particles with aqueous solutions of the surfactant p-dodecylbenzenesulfonic acid (DBSA) or the nonsurfactant p-toluenesulfonic acid (TSA). For the 26 nm particles, interfacial tension measurements indicate that p-dodecylbenzenesulfonic acid partitions between the particle surface and the oil-water interface, while p-toluenesulfonic acid remains on the particle surface. The partitioning of p-dodecylbenzenesulfonic acid supports the formation of emulsions, although in the absence of the particles the same surfactant concentration is not sufficient for emulsion stabilization. Due to the fast exchange kinetics, p-dodecylbenzenesulfonic acid is gradually replaced by particles. At equilibrium, the interfacial tension in the presence of the surface-modified particles is between the values for the pure particles and the pure surfactant solutions. However, the interfacial tension is independent of the surfactant concentration used in the preparation of the particles. Reducing the particle size to 8 nm leads to increased emulsion stability, and thus, the minimum particle concentration required to prepare stable emulsions was reduced to 0.1 g/L. However, above approximately 3.5 mmol/L of the sulfonic acids, the small particles dissolve slowly, and the emulsion stability is lost. This mechanism can be used to trigger the collapse of the emulsions.     

Conductometric and Gravimetric Studies of the Kinetics of Graphite Sedimentation in Aqueous Dispersions

The kinetics of graphite sedimentation in aqueous dispersions is studied using conductometric and gravimetric techniques. Triton X-305, a nonionic surfactant, is used to regulate the aggregation of hydrophobic graphite particles and to stabilize the system. The differences in the kinetics of the change in the weight and conductivity of sediments depending on the surfactant concentration are discussed. It is shown that insulating films of low conductivity are formed around particles at a concentration corresponding to coating of graphite particles with a monolayer of the surfactant and the conductivity of the sediments sharply decreases. At a higher surfactant concentration, which corresponds to the critical micellization concentration, compact sediments are formed; their conductivity first decreases and then increases in the process of restructuring. The change in the sediment structure as a function of the surfactant concentration is discussed.     

Effects of oligonucleotide adsorption on the physicochemical characteristics of a nanoparticle-based model delivery system for antisense drugs

Cationic polystyrene nanoparticles, as a model drug carrier system for nucleic acids, are capable of binding negatively charged oligonucleotides by multiple electrostatic interactions. The effect of the adsorption of phosphorothioate oligonucleotides on the physicochemical properties of the carrier system was investigated for uncoated and sterically stabilized latex particles. Turbidity measurements and photon-correlation spectroscopy indicate that the colloidal stability of the nanoparticle-oligonucleotide conjugates is influenced by the number of oligonucleotides adsorbed on the carrier. Especially in the case of the uncoated material, a destabilizing effect has been observed up to oligonucleotide concentrations of 2.7 μmol/g polymer. Strikingly, at higher concentrations the latexes exhibit colloidal stability similar to the oligonucleotide-free samples. These results were correlated to zeta-potential measurements demonstrating a reversal from positive to negative values of the zeta potential with increasing oligonucleotide concentration. The points of zero charge of the particles are in the region of maximum coagulation. These findings were compared to adsorption studies and calculations based on the random sequential adsorption model. It appears that at first the colloidal stability of the carrier systems is diminished with increasing oligonucleotide adsorption, while higher surface coverages lead to a significant reduction in coagulation. At the saturation level the surface coverage can be considered as a monolayer of “side-on” adsorbed molecules and the conjugates exhibit colloidal stability similar to the bare particles without adsorbed molecules. Received: 20 April 1998 Accepted: 16 July 1998     

Viscoelastic and shear viscosity studies of colloidal silica particles dispersed in monoethylene glycol (MEG), diethylene glycol (DEG), and dodecane stabilized by dodecyl hexaethylene glycol monoether (C12E6)

Silica dispersions stabilized by a nonionic surfactant, dodecyl hexaethylene glycol monoether (C 12E 6), were studied using rheological measurements. The viscosity-shear rate flow behavior of silica in monoethylene glycol (MEG) is shear thinning at low shear rates, leading to a Newtonian plateau at high shear rates for all dispersions studied. All rheological properties showed an increase above a critical surfactant concentration. The dispersions were stable at low levels of C 12E 6 concentrations because of electrostatic repulsions as deduced from the zeta potentials of silica that were on the order of about -30 to -65 mV in monoethylene glycol (MEG). Instability on further addition of C 12E 6 to the silica particles, a phenomenon normally obtained with high-molecular-weight polymers, was observed in MEG. Viscoelatic measurements of silica in monoethylene glycol at various surfactant concentrations showed a predominantly viscous response at low frequency and a predominantly elastic response at high frequencies, indicative of weak flocculation. Instability is explained in terms of hydrophobic and bridging interactions. Restabilization observed at high surfactant concentration was due to the steric repulsion of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion that moderated rheological measurements in glycol media and introduced the charge reversal of silica particles in dodecane.     

Adsorption and heterocoagulation of nonionic surfactants and latex particles on cement hydrates

The adsorption of nonionic surfactants of the alkyl-phenol-poly(ethylene oxide) family and of acrylic latex particles on several anhydrous (but hydrating) or fully hydrated mineral phases of Portland cement was studied. No or negligible adsorption of the surfactant was observed. This was assigned to the ionized character of the surface silanol groups in calcium-silicate-hydrates and to the strongly ionic character of the OH groups in calcium hydroxide and in the calcium-sulfoaluminate-hydrates, which prevents the formation of surface-ethoxy hydrogen bonds. In contrast, provided they are properly stabilized by the surfactant, the latex particles form a loose monolayer on the surface of hydrating tricalcium silicate particles. The attractive interaction between the positive mineral surface and the negative latex surface appears to be the driving force for adsorption. In line with this, adsorption is reduced by sulfate anions, which adsorb specifically onto the silicate surface. Compared to tricalcium silicate, portlandite and gypsum interact only marginally with the latex particles. Our results show that the stability of the nonionic surfactant/latex/cement systems is essentially controlled by the latex colloidal stability and the latex-cement interactions, the surfactant having little direct interaction, if any, with the mineral surfaces.