Biomedical subjects

J Masliyah

Publications and source records attributed to J Masliyah.

7 recordsLinked to original sources

PubMed2006

Probing colloidal forces between a Si3N4 AFM tip and single nanoparticles of silica and alumina.

The atomic force microscope (AFM) has been used to measure surface forces between silicon nitride AFM tips and individual nanoparticles deposited on substrates in 10(-4) and 10(-2) M KCl solutions. Silica nanoparticles (10 nm diameter) were deposited on an alumina substrate and alumina particles (5 to 80 nm diameter) were deposited on a mica substrate using aqueous suspensions. Ionic concentrations and pH were used to manage attractive substrate-particle electrostatic forces. The AFM tip was located on deposited nanoparticles using an operator controlled offset to achieve stepwise tip movements. Nanoparticles were found to have a negligible effect on long-range tip-substrate interactions, however, the forces between the tip and nanoparticle were detectable at small separations. Exponentially increasing short-range repulsive forces, attributed to the hydration forces, were observed for silica nanoparticles. The effective range of hydration forces was found to be 2-3 nm with the decay length of 0.8-1.3 nm. These parameters are in a good agreement with the results reported for macroscopic surfaces of silica obtained using the surface force apparatus suggesting that hydration forces for the silica nanoparticles are similar to those for flat silica surfaces. Hydration forces were not observed for either alumina substrates or alumina nanoparticles in both 10(-4) M KCl solution at pH 6.5 and 10(-2) M KCl at pH 10.2. Instead, strong attractive forces between the silicon nitride tip and the alumina (nanoparticles and substrate) were observed.

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PubMed2006

AFM colloidal forces measured between microscopic probes and flat substrates in nanoparticle suspensions.

Colloidal forces between atomic force microscopy probes of 0.12 and 0.58 N/m spring constant and flat substrates in nanoparticle suspensions were measured. Silicon nitride tips and glass spheres with a diameter of 5 and 15 mum were used as the probes whereas mica and silicon wafer were used as substrates. Aqueous suspensions were made of 5-80 nm alumina and 10 nm silica particles. Oscillatory force profiles were obtained using atomic force microscope. This finding indicates that the nanoparticles remain to be stratified in the intervening liquid films between the probe and substrate during the force measurements. Such structural effects were manifested for systems featuring attractive and weak repulsive interactions of nanoparticles with the probe and substrate. Oscillation of the structural forces shows a periodicity close to the size of nanoparticles in the suspension. When the nanoparticles are oppositely charged to the probes, they tend to coat the probes and hinder probe-substrate contact.

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PubMed2003

Shape relaxation of an elongated viscous drop.

The shape relaxation of a distorted viscous drop suspended in a quiescent immiscible liquid is analyzed in the creeping flow limit. The shape of the drop is axisymmetric, but otherwise arbitrary. The relaxation process is assumed to be driven by a constant interfacial tension and rate-limited by the Newtonian viscosities of the dispersed and continuous phases. For analysis, a least squares technique is developed which, compared to the more common boundary integral methods, is simpler to implement and especially suited for systems where one liquid is much more viscous than the other (i.e., when the viscosity ratio lambda, defined as the ratio of the dispersed to continuous phase viscosities, approaches either zero or infinity). To demonstrate the validity of the proposed least squares technique, its results are shown to agree well with boundary integral calculations for moderate values of lambda, and with experimental data when lambda is much larger than unity (approximately 10(6)). Predictions at infinite viscosity ratio--the regime in which the least squares technique is most useful--are then used to evaluate interfacial tensions associated with a system of practical importance, namely, the dispersion of heavy crude oil in an aqueous environment. This amounts to a novel and accurate technique for determining interfacial tensions--especially those of low values (1 mN/m or less)--between density-matched liquids where at least one of the phases is highly viscous. The experimental part of this study involves the use of suction pipettes to manipulate the shapes of individual micrometer-sized droplets, thus avoiding the need for complex flow-generating devices to create drop deformations.

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PubMed2003

Shear-induced coalescence of emulsified oil drops.

Crude oil droplets, when suspended in water, possess negative surface charges which give rise to double-layer repulsive forces between the drops. According to conventional DLVO theory, the magnitude of this repulsion (based on the measured zeta potential) is more than sufficient to prevent coalescence of the droplets. Indeed, when two such droplets were brought together on direct (i.e., "head-on") approach, coalescence was rarely observed. Upon oblique approach, however, the same droplets were seen to coalesce readily. An oblique encounter must necessarily give rise to lateral relative motion-or shearing-between the droplet surfaces. It is speculated that, if the charge distributions at the droplet surfaces were heterogeneous, lateral shearing would facilitate many encounters between surface patches of different zeta potentials across the intervening water film. If the repulsion across any local region were sufficiently weak to allow formation of an oil bridge across the water film, coalescence of the drops would follow inevitably. With the hypothesis of surface heterogeneity, it is not necessary to invoke any additional colloidal interactions (such as "hydrophobic forces") to account for the observed droplet-droplet coalescence. This finding may have important implications for the underlying mechanisms of emulsion stability in general and the commercial extraction of bitumen from oil sands in particular.

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PubMed2002

Bitumen-clay interactions in aqueous media studied by zeta potential distribution measurement.

A novel technique to investigate the interactions between bitumen and clays in an aqueous solution from the measurement of zeta potential distributions is described. For a single component suspension (i.e., clay or bitumen), a single modal zeta potential distribution was obtained under a given solution condition. In the case of a two-component (i.e., bitumen and clay) mixture system, the measured zeta potential distribution showed either one or two distribution peaks, depending on the chemical condition of the suspension and the type/amount of clays present. In the absence of added calcium ions, a mixture of bitumen emulsion and clay suspension exhibited two distinct zeta potential distribution peaks, corresponding to the peaks measured individually for the bitumen and clays, respectively. With the addition of 1 mM calcium ions, however, only one zeta potential distribution peak was obtained for the mixture of bitumen emulsion and montmorillonite clay suspension. Depending on the montmorillonite clay to bitumen ratio, the peak position in this case shifted toward the value for montmorillonite clay suspension alone. For kaolinite, the addition of 1 mM calcium ions did not cause a substantial change in the bimodal zeta potential distribution. The results suggest qualitatively a stronger interaction of bitumen with montmorillonite clay than with kaolinite clay, when calcium ions were present. The slime coating of montmorillonite clay on bitumen droplets in the presence of 1 mM calcium was validated. The conclusions obtained from this study further justified our mechanistic hypothesis for the observed depression of bitumen flotation by montmorillonite but not by kaolinite clay addition when calcium ions were added. This study demonstrated that zeta potential distribution measurement could be a powerful tool to study slime coating phenomena in a complex colloidal system.

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PubMed1999

Emulsification through Area Contraction.

Emulsification requiring very little input energy can be induced at an oil-water interface that is initially in a state of equilibrium. The process involves destabilization, through contraction, of local interfacial regions. For emulsification to occur, it is necessary for the interfacial structure to have no resistance to surface shearing. Such a mechanism of emulsification may have important implications for the approach to solving emulsion problems in the petroleum industry. Copyright 1999 Academic Press.

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PubMed1998

Does Equilibrium Interfacial Tension Depend on Method of Measurement?

In the presence of surfactants, the equilibrium interfacial tension (IFT) between two immiscible fluids can be very dependent on the particular technique used for measurement. This is because the partitioning of surfactants between the two bulk phases and the interface, which ultimately determines IFT, depends on geometric factors such as the volume fractions and specific interfacial areas (i.e., interfacial areas per unit volume) of the two fluids. In this work, the effect of surfactant partitioning on equilibrium IFT is demonstrated both theoretically and experimentally. A novel technique which enables direct measurement of IFT at macroemulsion droplet surfaces, with direct application to emulsion research, is demonstrated. Copyright 1998 Academic Press.

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