Jan Czarnecki

Thin liquid film technique — application to water–oil–water bitumen emulsion films

Abstract We describe an adaptation of the thin liquid film-pressure balance technique (TLF-PBT) for a systematic study of water/diluted-bitumen/water thin films. Recent research into the stability of water-in-oil emulsions, particularly those occurring in the oil industry, has not properly addressed the dependence of the emulsion stability on the thin films that are formed between approaching water droplets. The objective of this study is to obtain some insight into the mechanisms that stabilize the emulsion with particular attention to the relative importance of the resin, asphaltene, and solids fractions of the bitumen. Measurements of film lifetime and equivalent thickness indicated that the behavior of the film strongly depended on the type and concentration of solvent used to dilute the bitumen. Toluene-diluted-bitumen films drained continuously until a stable, uniform grey film was formed. Heptane-diluted-bitumen films formed black films covered with a scatter of small white dimples containing trapped liquid except at heptane:bitumen weight ratios of 10:1–15:1, where a network of fine white spots of unknown origin was formed. While the asphaltene and resin fractions alone provide a partially stable film, the combination of resin and asphaltene produced extremely stable films, a result that agrees well with emulsion studies by other researchers.

Micropipette: a new technique in emulsion research

Abstract Micron-scale studies on emulsions have, to date, been largely limited to the imaging of colloidal structures. In this communication, micropipette techniques are introduced as a progression beyond mere visualization: using small suction pipettes, mechanical experiments are performed on individual emulsion drops, from which interfacial properties can be deduced. To demonstrate this technique, the interfacial tension, emulsion stability and adsorption characteristics are directly assessed at the surfaces of micron-sized water droplets that are dispersed in crude oil.

Role of Asphaltenes in Stabilizing Thin Liquid Emulsion Films

Drainage kinetics, thickness, and stability of water-in-oil thin liquid emulsion films obtained from asphaltenes, heavy oil (bitumen), and deasphalted heavy oil (maltenes) diluted in toluene are studied. The results show that asphaltenes stabilize thin organic liquid films at much lower concentrations than maltenes and bitumen. The drainage of thin organic liquid films containing asphaltenes is significantly slower than the drainage of the films containing maltenes and bitumen. The films stabilized by asphaltenes are much thicker (40-90 nm) than those stabilized by maltenes (∼10 nm). Such significant variation in the film properties points to different stabilization mechanisms of thin organic liquid films. Apparent aging effects, including gradual increase of film thickness, rigidity of oil/water interface, and formation of submicrometer size aggregates, were observed for thin organic liquid films containing asphaltenes. No aging effects were observed for films containing maltenes and bitumen in toluene. The increasing stability and lower drainage dynamics of asphaltene-containing thin liquid films are attributed to specific ability of asphaltenes to self-assemble and form 3D network in the film. The characteristic length of stable films is well beyond the size of single asphaltene molecules, nanoaggregates, or even clusters of nanoaggregates reported in the literature. Buildup of such 3D structure modifies the rheological properties of the liquid film to be non-Newtonian with yield stress (gel like). Formation of such network structure appears to be responsible for the slower drainage of thin asphaltenes in toluene liquid films. The yield stress of liquid film as small as ∼10(-2) Pa is sufficient to stop the drainage before the film reaches the critical thickness at which film rupture occurs.

An electrokinetic model of drop deformation in an electric field

An electrokinetic model is proposed to describe a slight drop deformation which is induced by a weak external electric field. The fluids forming the system are considered Newtonian incompressible dielectric liquids containing free electric charge carriers. According to the model, the charge carriers take part in migration, diffusion and convection transport and there is no solute adsorption at the interface. Thermodynamic quasi-equilibrium at the interface is assumed for the charge carriers in the contacting liquids. The interfacial thermodynamic equilibrium is described using a common distribution coefficient for all the carriers. The problem is simplified by assuming equal diffusion coefficients for the different charge carriers within the same liquid. An analytical expression is obtained for slight drop deformation which is proportional to the second power of the applied field strength magnitude

Refractive index measurements of diluted bitumen solutions

Abstract The objective of this study was to obtain estimates for the refractive indices of bitumen, maltenes, and asphaltenes. Refractive index measurements performed on various bitumen–solvent mixtures were analyzed using a mixing model that related the refractive index of an ideal mixture to the refractive indices of the pure components of the mixture. Measurements could only be obtained for bitumen–solvent mixtures ranging in bitumen volume fraction from 0 to about 0.50. Extrapolation to a volume fraction of unity provided estimates of 1.584, 1.571 and 1.708 for the refractive indices of bitumen, maltenes, and asphaltenes, respectively. A precipitating solvent was also used to show that the onset of asphaltene precipitation could be detected from refractive index measurements. For a mixture of heptane and bitumen, the onset of asphaltene precipitation appeared to occur at a bitumen volume fraction of about 0.32.

Micron-scale tensiometry for studying density-matched and highly viscous fluids — with application to bitumen-in-water emulsions

Abstract Measuring the interfacial tension (IFT) between density-matched fluids has been a serious challenge in the study of tensiometry. These measurements can be further complicated when one or both of the fluids possess high viscosities. In this study, a micron-scale technique is developed to circumvent such difficulties. This microscopic technique involves stretching an otherwise spherical drop, of diameter ∼10 μm in an aqueous medium, with the use of two suction micropipettes; one of the pipettes is shaped as a cantilever to allow for measurement of the stretching force. It is shown that, for mechanical experiments conducted on the 1–10 μm scale, as in the present application, the gravitational body force and viscous effects can be neglected (provided relaxation times of several seconds are allowed). The Young–Laplace equation, which describes the force-drop deformation relation, is utilized to determine the equilibrium IFT. The system of present interest was that of bitumen drops in water at room temperature, in which the densities of the two phases are nearly equal (to within 1%) and the viscosity of bitumen is extremely high (more than 10 5 times that of water). This is the first study of bitumen–water (IFT) at room temperature over a range of pH.

Emulsion stability based on phase behavior in sodium naphthenates containing systems: gels with a high organic solvent content.

Addition of heptane to a sodium naphthenates/toluene/water system at 25 degrees C reduces the lamellar liquid-crystal phase range and increases the microemulsion phase range. Both of these effects result in the extension of the composition range where emulsions have low stability. This effect is even stronger at 40 degrees C. Heptane addition also results in the formation of very stable emulsions within the overlapping phase-existence ranges of aqueous (L1) and organic (L2) phases. Stable non-birefringent gel observed in equilibrium with L1 and L2 phases contains only a small percentage of water and sodium naphthenates. The swelling behavior of an unstable gel, an emulsion previously compressed by centrifugation, appears to be due to a stepwise thickening of the thin liquid films between the droplets.

Colloidal forces between emulsified water droplets in toluene-diluted bitumen

Abstract Interaction forces between two stable micron-sized water droplets in toluene-diluted bitumen have been studied by colloidal particle scattering, a method recently developed to determine surface forces between colloidal particles. Our results show that electrostatic forces contribute little or nothing to droplet stabilization. Instead, the stabilization mechanism is proposed to be steric repulsion between rough and non-homogeneous stabilizing layers on droplet surfaces. The range of possible thicknesses of the stabilizing layer is determined. The force–distance relationships reflecting this surface roughness are also plotted.

Electric field mediated breakdown of thin liquid films separating microscopic emulsion droplets

The authors present a microfluidic technique for electrically induced breakup of thin films formed between microscopic emulsion droplets. The method involves creating a stationary film at the intersection of two microchannels etched onto a glass substrate. After stabilizing the film, a ramped potential is applied across it. The electrical stresses developed at the film interfaces lead to its rupture above a threshold potential. The potential difference at which the film ruptures assesses the film stability. This approach is employed to demonstrate how surfactant (lecithin) adsorption imparts stability to an ultrathin oil film formed between two water droplets.

The effect of naphtha to bitumen ratio on properties of water in diluted bitumen emulsions

Abstract Properties of water in naphtha-diluted bitumen emulsion depend on naphtha to bitumen ratio. There is a critical dilution ratio, at which the system properties change abruptly. The critical dilution ratio coincides with an onset of asphaltene precipitation. The critical diluted ratio for the bitumen and naphtha used in this study is 4. At N/B