Hydrophobic Quartz Surfaces Research Articles

Molecular insights into oil detachment from hydrophobic quartz surfaces in clay-hosted nanopores during steam–surfactant co-injection

Thermal recovery techniques for producing oil sands have substantial environmental impacts. Surfactants can efficiently improve thermal bitumen recovery and reduce the required amount of steam. Such a technique requires solid knowledge about the interaction mechanism between surfactants, bitumen, water, and rock at the nanoscale level. In particular, oil sands ores have extremely complex mineralogy as they contain many clay minerals (montmorillonite, illite, kaolinite). In this study, molecular dynamics simulation is carried out to elucidate the unclear mechanisms of clay minerals contributing to the bitumen recovery under a steam–anionic surfactant co-injection process. We found that the clay content significantly influenced an oil detachment process from hydrophobic quartz surfaces. Results reveal that the presence of montmorillonite, illite, and the siloxane surface of kaolinite in nanopores can enhance the oil detachment process from the hydrophobic surfaces because surfactant molecules have a stronger tendency to interact with bitumen and quartz. Conversely, the gibbsite surfaces of kaolinite curb the oil detachment process. Through interaction energy analysis, the siloxane surfaces of kaolinite result in the most straightforward oil detachment process. In addition, we found that the clay type presented in nanopores affected the wettability of the quartz surfaces. The quartz surfaces associated with the gibbsite surfaces of kaolinite show the strongest hydrophilicity. By comparing previous experimental findings with the results of molecular dynamics (MD) simulations, we observed consistent wetting characteristics. This alignment serves to validate the reliability of the simulation outcomes. The outcome of this paper makes up for the lack of knowledge of a surfactant-assisted bitumen recovery process and provides insights for further in-situ bitumen production engineering designs.

Nanoscale Investigation into Dynamics of Thin Liquid Films during Bouncing and Attachment of Rising Air Bubbles on Hydrophilic and Hydrophobic Surfaces.

Investigations on bouncing and attachment of free-rising air bubbles on hydrophobic surfaces have been limited to side-view, high-speed photography of the bubble-plate attachment process. In this work, an investigation of the dynamics as well as stability of thin liquid films (TLFs) between free-rising air bubbles and quartz surfaces was performed using a newly developed multiple-wavelength synchronized reflection interferometry microscopy (SRIM) technique. The effect of surface hydrophobicity on both the stability and critical rupture thickness of TLFs was investigated. Results showed that the TLF ruptured at a critical rupture thickness of 100-1000 nm or beyond during bubble's impact on hydrophobic quartz surfaces. The critical rupture thicknesses varied depending on the surface hydrophobicity as well as surface asperity. A higher surface hydrophobicity, in general, contributed to a higher critical rupture thickness. In addition, the effect of n-octanol on the stability of the TLFs was investigated. Results showed that film stability increased with increasing the concentration of n-octanol, which was accompanied by a significant decrease in the critical rupture thickness. The present result illustrates, for the first time, the dynamics of TLFs on hydrophobic surfaces under a dynamic condition compared with previous studies under a quasi-equilibrium condition. The information revealed from the present work has a significant implication to many industrial applications, including froth flotation and other biological and semiconductor applications.

Reducing CO2 emissions and improving oil recovery through silica aerogel for heavy oil thermal production

Heavy oil reserves comprise more than 60% of global crude oil resources, and thermal oil recovery techniques, especially steam injection, are widely utilized for extracting heavy oil. However, these thermal production processes are characterized by high energy consumption and carbon emissions, which pose significant challenges in reducing CO2 emissions. In response to these challenges, this study presents a novel approach that combines silica aerogel with CO2-assisted thermal recovery technology. Our findings demonstrate that the incorporation of aerogel nanoparticles enhances the adsorption capacity of CO2 in the aqueous phase. The adsorption behavior of CO2 in silica aerogel aligns with the Langmuir model. When silica aerogel nanoparticles are employed in steam flooding, a notable improvement is observed in both oil recovery and CO2 sequestration rate. Molecular dynamics simulations reveal that the porous structure of aerogel enables the adsorption of light saturates molecules from crude oil, promoting their diffusion into the aqueous phase and ultimately enhancing oil recovery. The steam condensation experiments clearly demonstrate that the presence of aerogel and CO2 exerts a substantial influence on the condensation heat transfer of steam, resulting in a reduction in the condensation heat transfer rate between the steam and the cooling wall. Additionally, molecular dynamics simulations reveal that silica aerogel nanoparticles exhibit an affinity for adsorbing onto hydrophobic quartz surfaces, forming an insulating layer between steam and quartz, thereby facilitating CO2 sequestration. The introduction of silica aerogel nanoparticles expands the swept volume of steam heat. This study provides valuable insights into the underlying mechanisms responsible for improved CO2 sequestration and increased oil recovery through the implementation of silica aerogel nanoparticles, offering fresh perspectives on heavy oil recovery.

Molecular dynamics simulation of oil detachment from hydrophobic quartz surfaces during steam-surfactant Co-injection

In-situ recovery of bitumen involves high-temperature conditions yielded by a steam injection process, making it costly to produce, along with an extensive environmental footprint. From solvents to surfactants, additives come into play to tackle these issues efficiently. These additives can reduce a required amount of steam and increase bitumen recovery. Formulating surfactants for bitumen recovery under thermal process conditions requires solid knowledge about mechanisms and parameters incorporated into bitumen recovery. Molecular Dynamics (MD) simulation is carried out in this work to address unclear mechanisms that contribute to the bitumen recovery under a steam-anionic surfactant co-injection process. According to equilibrium MD simulation outputs, having sulfur on resin molecules can negatively affect an oil detachment process from a quartz surface due to changes in intermolecular interactions between different pairs of molecules inside a system, such as asphaltene-resin, asphaltene-asphaltene, and asphaltene-surfactant pairs. Under a flow condition, the composition of a resin fraction can change the threshold of a pumping force to detach oil from a quartz surface. During non-equilibrium MD simulation, increasing the pumping force strength from 10−5 to 10−4 Kcal/(mol.Ȧ) can improve the oil detachment process from the reservoir rock when the resin fraction contains sulfur. However, in the case of resin without sulfur, increasing the pumping force had a minor reduction in the oil detachment process. The outcomes of this paper will lay a solid foundation regarding mechanisms contributing to in-situ bitumen recovery, especially with chemical additives. Furthermore, they will provide a useful guidance for formulating chemicals applicable in the steam-chemical co-injection.

The Attraction of Water for Itself at Hydrophobic Quartz Interfaces.

Structural forces within aqueous water at a solid interface can significantly change surface reactivity and the affinity of solutes toward it. We show using molecular dynamics simulations how hydrophilic and hydrophobic quartz surfaces perturb the orientational structure of aqueous water, ultimately strengthening dipolar forces between molecules in proximity to the interface. When derived as a function of distance from each surface, it was found that both surfaces indirectly enhance the long-range dipolar attraction of water for itself toward the interfacial region. This was found to be longer-ranged for water molecules solvating the hydrophobic surface than those solvating the hydrophilic surface, with a range of up to 2.5 nm from the hydrophobic surface. Our results give direct quantification of surface-induced changes in solvent-solvent attraction, ultimately providing a counterintuitive addition to the balance of hydrophobic forces at aqueous-solid interfaces.

Measurement of Instability of Thin Liquid Films by Synchronized Tri-wavelength Reflection Interferometry Microscope.

Film thickness measurement of unstable thin liquid films (TLFs) remains a challenge due to the difficulty in determining the order of fringes prior to the film rupture. In the present work, a synchronized tri-wavelength reflection interferometry microscope (STRIM) was developed and employed to determine the spatiotemporal thickness profiles of the TLFs between air bubbles and various hydrophobic surfaces in 10-2 M NaCl solutions. Both accuracy and precision of film thickness measurements were found to be better than 3 nm over the range of 0-1 μm. It was found that when the radii of air bubbles were in the range 0.71-0.88 mm, the critical rupture thicknesses of the wetting films formed on hydrophobic quartz surfaces having water contact angles of 95° scattered over a range of 57-335 nm with a medium rupture thickness of 122 nm. For smaller air bubbles with radii of 0.13-0.26 mm, the critical rupture thicknesses were much more narrowly distributed with a medium rupture thickness of 27 nm. The result obtained with the TLFs between two air bubbles, i.e., foam film, showed that the critical rupture thickness was increased from 25 to 40 nm, when the sizes of air bubbles were increased from 220 to 960 μm. Compared to rupture thickness of the foam film, the critical rupture thickness of the TLF between an air bubble and a dodecane droplet was smaller, indicating that the film rupture might be related to the hydrophobicity of interacting surfaces. In addition to attractive surface forces, both wave motions and gas molecules in TLF might be associated with the film rupture.

Foam and wetting films: electrostatic and steric stabilization

Foam films and wetting films on quartz, obtained from aqueous solutions of two different surfactants [cetyltrimethylammonium bromide (CTAB) and PEO–PPO–PEO triblock copolymer (F108)] with NaCl as a background electrolyte, are considered as convenient models to compare the properties of symmetric (free thin liquid films) and asymmetric (thin liquid films on solid substrate) films with the same air/solution interface. Microinterferometric methodology of assessment of foam and wetting films is used to allow precise determination of the film thickness. In the case of CTAB films, experimental data for the potential ϕ 0 of the diffuse electric layer at the solution/air interface and the potential ϕ 1 at the solution/quartz interface are used to analyze the stability of the films studied. A conclusion drawn is that electrostatic interaction forces stabilize both kinds of films studied. It is shown that with increasing CTAB concentration a charge reversal occurs at both the solution/air and solution/quartz interfaces that determines the stability/instability of the foam and wetting films. Concentration ranges where both types of films produce stable (equilibrium) films are found. There are also concentration ranges where the films either rupture or are metastable (quasi-equilibrium). The CTAB concentration ranges, which provide formation of unstable (rupturing and metastable) and stable films, are different for symmetric (foam) and asymmetric (wetting) thin liquid films. It is only at high CTAB concentrations (>2×10 −4 mol dm −3) that both cases render formation of stable equilibrium films. In the case of F108 films, the comparison of foam films and wetting films on quartz indicates film stability that is either electrostatic or steric in origin. On the basis of the effect of electrolyte concentration on film thickness, the transition from electrostatic to steric stabilization is demonstrated for both kinds of films. The critical electrolyte concentration at which this transition occurs is determined. Foam films are found to be always stable (equilibrium). Formation of either unstable (rupturing and metastable) or stable (equilibrium) wetting films on quartz is established depending on the solution composition. The effects are similar for both hydrophilic and hydrophobic quartz surfaces. The results obtained show certain similarity between foam and wetting films. In both cases, electrostatic forces below the critical electrolyte concentration, and above it steric forces govern film stability. Some specific properties of the wetting films are induced by the asymmetric boundary conditions as distinct from symmetric foam films.

Experimental evidence of the reversibility of the first stage of protein adsorption at a hydrophobic quartz surface near the isoelectric point

AbstractThe reversibility of the first stage of adsorption of zwitterionic cytochrome c on a hydrophobic quartz surface was investigated using time‐resolved slab optical waveguide (SOWG) absorption spectroscopy. Using a novel prism‐free broadband coupling approach, absorbance data were collected successfully at a 50 ms time interval during the first few seconds after solution–surface contact. Near the isoelectric point where the cytochrome c molecules possess a net charge of zero and hence cannot be influenced by an electric field, the speed at which adsorption proceeded was found to be dependent on cytochrome c concentration as well as on surface hydrophobicity. It was also observed that the degree of protein adsorption increased as the surface hydrophobicity was increased. Within 6 s the adsorption process appeared to be reversible, as revealed by extremely low chi‐squared values when the absorbance data were fitted into the reversible Langmuir‐type kinetic model. The standard Gibbs free energy of adsorption was also calculated from the absorbance data. Copyright © 2003 John Wiley & Sons, Ltd.

Effect of interfacial phenomena on dewetting in dropwise condensation

Image-analyzing interferometry was used to investigate the dynamics of the dewetting meniscus of a partially wetting fluid on a modified quartz surface during dropwise condensation. The vivid difference in the behavior of the retracting meniscus with respect to its variation in apparent contact angle and curvature after the merger of the drop with the meniscus was found to depend on the wettability of the surface. On the hydroxylated quartz surface, the meniscus shed mass during retraction. The dewetting velocity decreased with time. On a slightly hydrophobic quartz surface, the meniscus showed a curvature gradient in the axial direction during drop merger and that gradient decreased as the meniscus moved towards the corner. The dewetting of the meniscus is discussed using the interfacial concepts of spreading and the Kelvin–Clapeyron phase change model.

The adsorption of water and amino acids onto hydrophilic and hydrophobic quartz surfaces

The adsorption of (a) serine and leucine and (b) water onto hydrophilic and hydrophobic surfaces was investigated using the radio tracer technique. (a) Films only a fraction of a monolayer (serine 0.45 and leucine 0.30 monolayers as maximum) in thickness were formed. The free energy of adsorption of leucine was found to be 1.147 times greater than that of serine on a hydrophobic surface, and about 1.38 times greater on a hydrophilic surface, i.e. leucine showed a higher affinity of binding onto both surfaces than serine did. Independent of whether serine or leucine is used, the surface concentration is higher on hydrophilic than on hydrophobic surfaces. Furthermore, both amino acids showed a decrease in the adsorption rate at high bulk concentration except for leucine (on a hydrophobic surface) where the surface density increased linearly with bulk concentration. This linear relation was probably an effect of the medium that screened the electrostatic and hydrophobic side-chain interactions. (b) An accelerating rate of adsorption was observed at surface coverage >0.04 of a monolayer indicating strong lateral interactions among adsorbed water molecules. Both isotherms show a high sticking probability coefficient and a saturation level at high bulk concentration. The surface concentration of water (≈ 5–6 monolayers) on a hydrophilic surface was found to be approximately 1.7 times greater than that on a hydrophobic surface.

Interaction and stability of adsorbed ferritin clusters on hydrophobic quartz surfaces

Ferritin adsorption on a hydrophobic quartz surface was measured at different bulk concentrations and adsorption times. The initial slope of the isotherms increases with increasing bulk concentration. The pair correlation function, g( r), was obtained from the spatial distribution of adsorbed ferritin molecules on a quartz surface. The potential of average force was found to be around 1.4 kT, and clusters that are kept together by this potential are found to be stable only for less than a second. Ferritin molecules adsorbed on a hydrophobic quartz surface at low concentration (1 mg l −1) were found to interact at distances up to 5 radii. A theoretical model describing the kinetics of adsorption, desorption and cluster dissociation on an ideal surface was also derived.

The drainage of a thin aqueous film between a solid surface and an approaching gas bubble

A new optical technique is used to measure the time-dependent shape of thin aqueous draining films between air bubbles and hydrophilic or hydrophobic quartz surfaces. The thickness is determined to a precision of ±0.2 nm to ±1 nm from the intensity of the reflected interference beam from a spot of laser light which is focussed on the thinning film and which is scanned radially. The film shape begins as a dimple which then flattens as it thins. Plots of the thickness as a function of time and of radial position are presented for films of pure water and of 0.23 mol m −3 NaCl solution at hydrophilic quartz surfaces. In the ring of closest approach, the pure water film is at all times thicker than that of the salt solution film. In the early phase of the approach, the pure water film thins more slowly at the centre, but after about 40 s it thins more rapidly. Both of these observations are consistent with the expected shorter range of the double layer repulsion in the salt solution. For hydrophobic surfaces, the drainage rate is more rapid, the film eventually collapsing.