Sili Ren

Interaction forces between a deformable air bubble and a spherical particle of tuneable hydrophobicity and surface charge in aqueous solutions.

Interaction forces between an air bubble and a spherical particle of moderate and tuneable surface charge density and hydrophobicity in aqueous solutions were measured using atomic force microscopy. Bitumen coated silica spheres were used as model particles of tuneable charge density and hydrophobicity due to pH-dependent ionisation of carboxylic acids at bitumen-water interfaces. The measured force profiles showed a long-range repulsion prior to jump into contact, indicating the rupture of intervening liquid film between the bitumen and bubble surfaces. The long-range repulsive force increased with increasing pH. The measured force profiles were analysed by adopting the model originally developed by White and co-workers to account for deformation and change in shape of bubbles before rupture of the intervening liquid film. Satisfactory agreement between the theory and measured force profiles was obtained, showing the suitability of the model to describe the measured interaction forces. The model was then used to study the physical parameters on the particle-bubble interaction forces prior to three phase contact line (TPCL) formation. The hydrophobic decay length, surface potential and size of bubble and probe particles, and ionic strength of the medium (KCl concentration) were found to have a strong influence on the predicted force profiles.

Separation of Emulsified Oil from Oily Wastewater by Functionalized Multiwalled Carbon Nanotubes

Rapid separation of emulsified oil from oily wastewater is one of the most serious challenges faced in the petroleum industry. In this study, a rapid and efficient demulsifier, functionalized multiwalled carbon nanotubes (F-MWCNTs), was prepared and used to separate the emulsified oil from oily wastewater. Demulsification test showed that the oil removal efficiency could attain as high as 99.8% at an optimal condition within a few minutes. The micro-morphology of the oil–water mixture before and after demulsification was observed using a polarizing microscope. It was found that the fine oil droplets experienced a rapid coalescence to form oil phase floating on the water surface. Mechanism of the demulsification process was discussed. The introduction of the functional groups (such as ‒OH and ‒COOH) on the surfaces of F-MWCNTs enable them good amphiphilicity and therefore easily arriving at the oil/water interface to destroy the interfacial protective film mainly composed of asphaltenes and resins. The findings in this work showed that the F-MWCNT is an efficient nanomaterial to remove emulsified oil from the oily wastewater and might have wide application prospects in the petroleum industry. GRAPHICAL ABSTRACT

Demulsification of heavy oil-in-water emulsions by reduced graphene oxide nanosheets

A series of reduced graphene oxide (rGO) materials was synthesized by simple, clean, and controlled hydrothermal reduction of graphene oxide (GO). The chemical composition and properties of the obtained rGO materials were characterized by FT-IR, UV-visible absorption spectroscopy, XPS, AFM, zeta potential measurement, and interfacial tension analysis. As two-dimensional surfactants, various samples of rGO were employed to demulsify an oil-in-water emulsion. The demulsification performance of various demulsifiers was found to be considerably improved with increasing the reduction degree of the GO. In particular, the demulsification efficiency could reach about 99.97% for the rGO-110 sample. Quantum chemical calculations with a high quantum level of density functional theory with the empirical dispersion corrections approach (DFT-D) were performed to understand the mechanism of demulsification. The results revealed that rGO has a stronger adsorbability for asphaltene molecules than GO does by π–π interaction. Due to the strong π–π interaction between the rGO nanosheets and the asphaltenes, the protective film stabilizing the oil-in-water emulsion was more easily destroyed, thus promoting the oil droplets to coalesce to realize the separation of oil from water.

Functionalized carbon black nanoparticles used for separation of emulsified oil from oily wastewater

ABSTRACT Functionalized carbon black (F-CB) nanoparticles were synthesized by covalently grafting the polyvinyl alcohol on carbon black (CB) surfaces and used as demulsifier to separate the oil from the emulsified oily wastewater. The bottle test showed that the residual oil content in the separated water was as low as ∼50 mg/L corresponding to a demulsification efficiency of about 99.90% at an optimal condition within a few minutes. It was believed that the surface wettability of the carbon black could be tuned by modifying with the PVA molecules, which enables the F-CB nanoparticles to be readily migrated to the oil/water interface and have the opportunity to interact with and/or displace the stabilizers of the emulsion. As a result, the demulsification process was accomplished with the coalescence of the oil droplets promoted by the F-CB nanoparticles. The interaction behavior between F-CB nanoparticles and asphaltenes was investigated by quantum chemical calculations. The results showed that the F-CB nanoparticles have strong interaction with the asphaltene molecules in form of π−π and θ−π forces. The findings in present study are significant for understanding the demulsification mechanism and also provide a novel demulsifier for the demulsification of emulsified oily wastewater. GRAPHICAL ABSTRACT

Dependence of Colloidal Forces Between Bitumen and Silica on the Chain Lengths of Ammonium Surfactants

Effects of ammonium surfactants with different hydrocarbon chain lengths (C8, C12, C16, and C18) on the colloidal forces between bitumen and silica were studied by atomic force microscopy. The results showed that the chain length of the ammonium surfactants had a significant impact on both the long-range interaction and adhesion forces. With the addition of surfactants with relative short chains of C8 and C12 in the solutions, the long-range repulsive force decreased or even became strong attractive force, while it became repulsive again in solutions of surfactants with long chains of C16 and C18. It was further observed that addition of Ca2+ in various surfactants solutions would either depress or enhance the colloidal interactions based on the surfactant chain lengths. It was believed that variation of the interaction behaviors resulted from the mono-layer or bilayer adsorption of various surfactant molecules on the negatively charged surfaces of bitumen and silica, which affected the surface wettability and the surface charge characteristics and then greatly changed the colloidal interactions. The findings indicated that, to have a high bitumen recovery and good froth quality, the surfactant type and concentration of the di-valent metal ions in the oil sand processing slurry must be well considered. GRAPHICAL ABSTRACT

Construction of Various Self-assembled Films and Their Application as Lubricant Coatings

Recently, self-assembled nanofilms (SANFs), including self-assembled monolayers (SAMs), self-assembled multilayer films (SAMFs), self-assembled inorganic films (SAIFs) and selfassembled organic-inorganic composite films (SAO-ICFs), have generated substantial interest not only for its simple preparation procedure but also for its wide potential applications in many fields, such as surface modification, boundary lubricant coatings, sensors, photoelectronics, and functional bio-membrane modeling, etc (Foisner et al., 2004; Gulino et al., 2004; Hsu, 2004; Love et al., 2005; Ostuni et al., 1999; Song et al., 2008; Ulman, 1996; Wang et al., 2005). As a potential lubricant film for controlling stiction and friction in micro-/nano-electromechanical systems (MEMS/NEMS), SANFs offers distinct advantages over other strategies for lubrication of MEMS/NEMS devices. Especially, its assembly process is rapid, shape independent and needs no complicated equipment (Ulman, 1996). In general, the molecules can be assembled onto the targeted surfaces by a simple solution immersion or vapor phase deposition, even within nanoscale crevices between moving components of MEMS/NEMS. To date, the adhesion, friction and wear behaviors of SANFs are extensively investigated in nanoscale and macroscale by using various techniques and apparatus. Scanning force microscope (SFM) techniques, mainly including atomic force microscope (AFM) (Butt et al., 2005), interfacial force microscope (IFM) (Houston & Michalske, 1992), and chemical force microscope (CFM) (Noy et al., 1997), are often applied to evaluate the nanotribological performances of thin films. In AFM, the adhesive force between the AFM tip and the surface can be calculated from the “force-distance” curve (Cappella & Dietler, 1999) as follows (Tsukruk & Blivnyuk, 1998; Xiao & Qian, 2000):