DLVO surface forces in liquid films and statistical mechanics of colloidal oscillatory structural forces in dispersion stability.

This paper focuses on the theory of the dispersion stability considering two models. In the classical DLVO model of surface forces, the interactions between two particles consist of two terms: the London-van der Waals attractive interaction and the electrostatic repulsive interaction in the frame of the Debye-Hückel theory. The solvent, the aqueous solution of the electrolyte, was considered the continuous phase.

The foam film's stepwise thinning phenomenon and role of oscillatory forces.

As a foam film formed from complex fluids thins, the particles under the film confinement self-organize into layers. Reflected light was used to monitor the rate of layer-by-layer thinning and the layers' thickness. The microscopic and macroscopic films thin using the same stepwise manner (stratify), via layers or stripes with equal thicknesses.

Methods to monitor water-in-oil film thinning and stability: An application to bitumen demulsification.

Understanding what governs the water-in-oil emulsion film stability and demulsification is important for science and technology. The demulsification of the tar sands' water-in-bitumen emulsion and proposing methods for demulsification with an efficient demulsifier (emulsion breaker) are important but challenging tasks. Despite the long period of time researchers have been examining the factors governing bitumen emulsion stability and demulsification, these concepts are still not well understood and require more study.

How the capillarity and ink-air flow govern the performance of a fountain pen.

As kids, the authors enjoyed learning how to write by dipping nib pens into ink, and then later, using flex nib pens for calligraphy. They remember, less fondly, the troubles with ink leaks and spills over the paper's surface. Despite advances in fountain pen design, the performance of fountain pens is still not perfect.

Novel approach for calculating the equilibrium foam nanofilm-meniscus contact angle and the film free energy.

The film meniscus is a capillary system that is part of everyday observed phenomena, such as in foams, emulsions, liquid suspensions of nanoparticles (nanofluids), and liquid-wetting solids. The capillarity of a microscopic free foam lamella with a meniscus is important for a fundamental understanding of the role of the surface forces vs. thickness and stability of dispersed systems.

Air bubble bursting phenomenon at the air-water interface monitored by the piezoelectric-acoustic method.

When an air bubble arrives at the free interface, the bubble's lamella drains and ruptures. The bubble collapses, and gas vapor is released. The ruptured lamella retreats, and a rim at the edge of the retreating lamella forms.

Structure and stability of nanofluid films wetting solids: An overview.

When an air bubble or an oil droplet in a nanofluid (liquid containing dispersed nanoparticles) approaches a solid surface, a nanofluid film is formed between the bubble or drop and a solid substrate. The nanoparticles confined in the film surfaces tend to self-layer and the film thins in a stepwise manner. The wetting behavior and film stability criteria valid for the classical molecularly thin films cannot be applied to nanofilm.

Two-phase displacement dynamics in capillaries-nanofluid reduces the frictional coefficient.

Surfactant solutions containing polymeric nanoparticles have been shown to have an improved wetting and spreading on solid surfaces. In this work, we explored the effect of the polymeric nanoparticles on the frictional coefficient at the three-phase contact region by studying polymeric nanofluids displacing oil in capillaries. Our results show polymeric nanoparticles can reduce the frictional coefficient by as much as four times by forming structured layers in the confined wedge film.

Tears of wine: The dance of the droplets.

For a long time, the phenomenon known as the "tears of wine" was believed to be due only to the surface tension gradient (e.g., the Thomson-Marangoni stress on the fluid/fluid surface's dynamics of wetting) and gravity.

Prediction of the rate of the rise of an air bubble in nanofluids in a vertical tube.

Our recent experiments have demonstrated that when a bubble rises through a nanofluid (a liquid containing dispersed nanoparticles) in a vertical tube, a nanofluidic film with several particle layers is formed between the gas bubble and the glass tube wall, which significantly changes the bubble velocity due to the nanoparticle layering phenomenon in the film. We calculated the structural nanofilm viscosity as a function of the number of particle layers confined in it and found that the film viscosity increases rather steeply when the film contains only one or two particle layers. The nanofilm viscosity was found to be several times higher than the bulk viscosity of the fluid.

Estimation of structural film viscosity based on the bubble rise method in a nanofluid.

When a single bubble moves at a very low capillary number (10) through a liquid with dispersed nanoparticles (nanofluid) inside a vertical tube/capillary, a film is formed between the bubble surface and the tube wall and the nanoparticles self-layer inside the confined film. We measured the film thickness using reflected light interferometry. We calculated the film structural energy isotherm vs.

Enhanced oil displacement by nanofluid's structural disjoining pressure in model fractured porous media.

Nanofluids for improved oil recovery has been demonstrated through laboratory corefloods. Despite numerous experimental studies, little is known about the efficacy of nanofluids in fractured systems. Here, we present studies of nanofluid injection in fractured porous media (both water-wet and oil-wet) formed by sintering borosilicate glass-beads around a dissolvable substrate.

Structural disjoining pressure induced solid particle removal from solid substrates using nanofluids.

Nanofluids comprising nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of a nanofluid on a solid substrate has revealed that the structural disjoining pressure gradient caused by the layering of the nanoparticles normal to the confining plane of the film with the wedge profile is a new mechanism for oily soil detachment from the solid substrate. In the present work, we explore the application of this new mechanism for the solid particle detachment using latex particles on glass and a copper-coated wafer substrate using nanofluids.

Escherichia coli removal from model substrates: Underlying mechanism based on nanofluid structural forces.

Understanding the interactions between bacteria and solid surfaces that result in bacterial adhesion and removal is of immense importance for reducing foodborne illness outbreaks. A nanofluid formulation comprised of a sodium dodecyl sulfate (SDS) micellar aqueous solution in the presence of an organic acid (as a pH controller) was used to test the E. coli K12 removal from two substrates, polyvinylchloride (PVC) and partially hydrophobic glass.

Step-Wise Velocity of an Air Bubble Rising in a Vertical Tube Filled with a Liquid Dispersion of Nanoparticles.

The motion of air bubbles in tubes filled with aqueous suspensions of nanoparticles (nanofluids) is of practical interest for bubble jets, lab-on-a-chip, and transporting media. Therefore, the focus of this study is the dynamics of air bubbles rising in a tube in a nanofluid. Many authors experimentally and analytically proposed that the velocity of rising air bubbles is constant for long air bubbles suspended in a vertical tube in common liquids (e.

Stepwise dynamics of an anionic micellar film - Formation of crown lenses.

We studied the stepwise thinning of a microscopic circular foam film formed from an anionic micellar solution of sodium dodecyl sulfate (SDS). The foam film formed from the SDS micellar solution thins in a stepwise manner by the formation and expansion of a dark spot(s) of one layer less than the film thickness. During the last stages of film thinning (e.

Capillary dynamics driven by molecular self-layering.

Capillary dynamics is a ubiquitous everyday phenomenon. It has practical applications in diverse fields, including ink-jet printing, lab-on-a-chip, biotechnology, and coating. Understanding capillary dynamics requires essential knowledge on the molecular level of how fluid molecules interact with a solid substrate (the wall).

Stepwise thinning dynamics of a foam film formed from an anionic micellar solution.

Liquid films formed from a surfactant micellar solution thin in a stepwise fashion (stratify): the film thickness decreases layer-by-layer and dark spots appear (areas of the film with one micellar layer less than their surroundings). In a recent paper [Langmuir2016, 32, 4837-4847], we presented a two-dimensional diffusion model to explain the expansion of the dark spots inside the foam film formed from a nonionic surfactant micellar solution. Here, we apply the model to explain the dark spot expansion in the foam film formed from an anionic surfactant micellar solution of sodium dodecyl sulfate.

Oil lenses on the air-water surface and the validity of Neumann's rule.

Many studies have focused on the mechanisms of oil spreading over the air-water surface, oil lens formation, and lens dynamics: Franklin et al.(1774), Rayleigh (1890), Neumann and Wangerin (1894), Hardy (1912), Lyons (1930), Langmuir (1933), Miller (1941), Zisman (1941), Pujado and Scriven (1972), Seeto et al. (1983), and Takamura et al.

Stratification of a Foam Film Formed from a Nonionic Micellar Solution: Experiments and Modeling.

Thin liquid films containing surfactant micelles or other nanocolloidal particles are considered to be the key structural elements of foams containing gas and liquid. We report here the experimental results and theoretical modeling for the phenomenon of the stratification (stepwise thinning) of a foam film formed from a nonionic micellar solution. The film stratification phenomenon was experimentally observed by reflected light microinterferometry.

The dynamic spreading of nanofluids on solid surfaces - Role of the nanofilm structural disjoining pressure.

Nanofluids comprising nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of an aqueous film containing nanoparticles displacing an oil droplet has clearly revealed that the structural disjoining pressure arises due to the layering of the nanoparticles normal to the confining plane of the film with the wedge profile. The pressure drives the nanofluid in the wedge film and the nanofluid spreads.

Rise of the main meniscus in rectangular capillaries: Experiments and modeling.

The rise of the main meniscus in rectangular capillaries is important in interpreting the phenomenon of fluid flow in porous media. Despite many experimental studies reported in the literature, there is no universal model for the rise of the main meniscus in either rectangular or square capillaries. In this work, we present an extensive experimental study and modeling of the rise of the main meniscus in both square and rectangular capillaries.

Nanofluids alter the surface wettability of solids.

We report the results of our studies on the changes in the contact angle and interfacial tension using a nanofluid composed of silica nanoparticles dispersed in water on three different solid substrates: gold (partially hydrophobic), glass (hydrophilic), and a silicon wafer (hydrophilic). We used both the goniometric method and drop-shape analysis to make the measurements. On the basis of the results of the drop-shape analysis using the Laplace equation, we evaluated the contributions of the interfacial tension change to the equilibrium contact angle and the presence of nanoparticles near the solid substrate, thereby elucidating the change in the wettability of the solid substrate.

Dewetting film dynamics inside a capillary using a micellar nanofluid.

An experimental study was performed in which hexadecane was displaced by a micellar nanofluid in a glass capillary. Experiments have shown that a thick film was formed on the capillary wall after hexadecane was displaced by the nanofluid. The thick hexadecane film is unstable, and over time it breaks and forms a thin film.