Colloids Interfaces, Volume 2, Issue 2 (June 2018) – 12 articles

Carbonic anhydrase (CA) is a hydrolase enzyme possessing an active center composed of three histidines (His), zinc(II) (Zn²⁺), and a hydration water. Here we report the hydrolase-like catalytic activity provided by the oleoyl-histidine (O-His) modified on liposome membranes. O-His was synthesized by the amide bond between oleic acid and His, and was incorporated into 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes. The hydrolysis of p-nitrophenylacetate was promoted by O-His modified DOPC liposomes in the presence of Zn²⁺. The formation of the active center was revealed by UV resonance Raman spectra. We conclude that the liposome membrane surface can be utilized as a platform for artificial hydrolysis reactions by modifying essential ligands inspired from natural enzymes. Full article

In this study, we examine microscale waterflooding in a randomly close-packed porous medium. Three different porosities were prepared in a microfluidic platform and saturated with silicone oil. Optical video fluorescence microscopy was used to track the water front as it flowed through the porous packed bed. The degree of water saturation was compared to water containing two different types of chemical modifiers, sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP), with water in the absence of a surfactant used as a control. Image analysis of our video data yielded saturation curves and calculated fractal dimension, which we used to identify how morphology changed the way in which an invading water phase moved through the porous media. An inverse analysis based on the implicit pressure explicit saturation (IMPES) simulation technique used mobility ratio as an adjustable parameter to fit our experimental saturation curves. The results from our inverse analysis combined with our image analysis show that this platform can be used to evaluate the effectiveness of surfactants or polymers as additives for enhancing the transport of water through an oil-saturated porous medium. Full article

The heavy metals removal efficiency of synthetic NaX zeolite has been studied. The sorbent was fully characterized by nitrogen sorption, X-ray diffraction, FT-IR and scanning electron microscopy. The batch sorption tests were performed taking into consideration several factors such as m/V ratio, contact time, pH and initial metal ions concentration. The maximum sorption capacities were 3.45, 3.86 and 4 mmol g⁻¹ for Pb²⁺, Cd²⁺ and Cu²⁺, respectively. Fixed-bed experiments were carried out to test the applicability of NaX zeolite as well as column regeneration experiments. Full article

The wettability of solids by aqueous solutions of surfactants is very important in many practical applications. Thus, the measured advancing contact angles of aqueous solutions of chosen surfactants on polyethylene (PE) and those taken from the literature on polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), and polyamide (nylon 6) were analyzed. Based on the measured values of the contact angles and the literature data of the surface tensions of the studied surfactant solutions, their adsorption at the PE–water interface and the work of adhesion (W_a) were determined. The values of W_a to PE calculated on the basis of the contact angles and surface tensions of these solutions were compared to those determined by applying the new Lifshitz–van der Waals component of the water–PE surface tension. There was a good agreement between the W_a values determined in two different ways. Their contact angles were calculated using the values of PE surface tension, the new Lifshitz–van der Waals component of the water surface tension, and the surface tension of aqueous solutions of the studied surfactants. The contact angle values calculated in such a way were close to the measured values. In the case of PTFE, the same relations were obtained. The values of W_a to PMMA and nylon 6 could be also predicted. Full article

Carbonate rock reservoirs comprise approximately 60% of the world’s oil and gas reserves. Complex flow mechanisms and strong adsorption of crude oil on carbonate formation surfaces can reduce hydrocarbon recovery of an oil-wet carbonate reservoir to as low as 10%. Low salinity waterflooding (LSW) has been confirmed as a promising technique to improve the oil recovery factor. However, the principal mechanism underpinning this recovery method is not fully understood, which poses a challenge toward designing the optimal salinity and ionic composition of any injection solution. In general, it is believed that there is more than one mechanism involved in LSW of carbonates; even though wettability alteration toward a more desirable state for oil to be recovered could be the main cause during LSW, how this alteration happens is still the subject of debate. This paper reviews different working conditions of LSW, previous studies, and field observations, alongside the proposed interfacial mechanisms which affect the colloidal interactions at oil–rock–brine interfaces. This paper provides a comprehensive review of studies on LSW in carbonate formation and further analyzes the latest achievements of LSW application in carbonates, which helps to better understand the challenges involved in these complicated multicomponent systems and potentially benefits the oil production industry. Full article

An efficient process was developed allowing the removal of metal ions from polycontaminated aqueous solutions by combining modified colloids and membranes. Firstly, filtration experiments were performed using polyethersulfone membranes modified by a self-assembled multilayer film of polyelectrolytes. These polymer-modified membranes allowed the uptake of more than 90% of the metal ions initially present in the contaminated solutions (for solutions concentrated at 50 mg L⁻¹). Secondly, adsorption experiments were carried out with colloidal silica encapsulated with carboxymethyl chitosan (SiO₂-CMCS) or with mesoporous silica functionalized by grafting of 1,4,8,11-tetraazacyclotetradecane, i.e., cyclam (SiO₂-cyclam). The adsorption capacity of these compounds was shown to be higher than numerous other literature-known adsorbents, reaching 68 and 61 mg g⁻¹ towards Cu(II) for SiO₂-CMCS and SiO₂-cyclam, respectively. Finally, by coupling adsorption with ultrafiltration in the tangential mode, the removal of Cu(II), Ni(II) and Zn(II) ions was found to be improved, allowing to reach a removal efficiency of 99% towards Cu(II), Ni(II) and Zn(II) ions at a metal concentration of 50 mg L⁻¹, and a promising removal efficiency around 70% at a very high metal concentration of 1200 mg L⁻¹. The mechanisms involved in the capture of the metal ions by modified membranes and colloids are also discussed. Full article

The equilibrium profile of a single floating particle is numerically investigated using transformed equations depending on the inclination angle of the deformed surface, which is governed by the Young–Laplace equation. The relationship between the depth far from the flat interface and the filling angle is derived from the force balance acting upon the particle. The Chebyshev nodes are employed as a discretization for the inclination angle and yield satisfactory results for computation. The computational results show that this is an efficient way to analyze the deformed surface around floating particles with an infinity boundary condition. The static profile of the free surface around the spherical particle is largely dependent on the density ratio and the contact angle. Full article

Mixed fatty acids or mixed phospholipids systems with saturated-unsaturated hydrocarbon chains are of biological interest. In this work, the monolayers of oleic acid-stearic acid (OA-SA) and palmitoyloleoylphosphatidylcholine-dipalmitoylphosphatidylcholine (POPC-DPPC) have been studied. From the surface pressure-area isotherms, elastic modulus values and virial equation coefficients can be obtained. Thermodynamic treatment also yields excess (G^E) and mixing (ΔG_mix) free energies. Results indicate positive G^E values, that is, molecular interactions in the mixed films are less favourable, due to the presence of unsaturation; however, the mixture is slightly favourable due to the entropic factor that affords positive ΔG_mix values. For the OA-SA system, a high SA content and surface pressure facilitate the phase separation, even though a certain miscibility between both components still remains. For the POPC-DPPC system, the most favourable mixing conditions occur for X_POPC ≈ 0.4. For these mixed systems, the values of the elastic modulus are more similar to those of more fluid components (OA or POPC); analysis of the virial coefficients shows that the b₁ virial coefficient values lie between those of the individual components and are higher than values suitable for an ideal mixing. Full article

In this article, the importance of colloids and interfaces in thermal heavy oil or bitumen extraction methods is reviewed, with particular relevance to oil sands. It begins with a brief introduction to the chemical composition and surface chemistry of oil sands, as well as steam-based thermal recovery methods. This is followed by the specific consideration of steam-assisted gravity drainage (SAGD) from the perspective of the interfacial chemistry involved and factors responsible for the displacement of bitumen from reservoir mineral surfaces. Finally, the roles of the different chemical additives proposed to improve thermal recovery are considered in terms of their contributions to recovery mechanisms from interfacial and colloidal perspectives. Where appropriate, unpublished results from the author’s laboratory have been used to illustrate the discussions. Full article

Microscopic surface architectures that can be easily manufactured have been in demand as mechano-structural cues for tissue engineering. Microscopic surface reliefs synthesized by wrinkling were expected as cell culture scaffolds for cell proliferation, control of cellular alignment and differentiation, and spheroid generation. We previously developed bio-based wrinkled films prepared via lignification-mimetic reactions and drying. Although these films are expected as a candidate for cell culture scaffolds, stability and morphology of the wrinkled surfaces in aqueous buffer solutions were not explored. Here, we investigate the surface morphologies of the wrinkled films in phosphate-buffered saline, and their application to 3T3 cell culture. The wrinkled film prepared with the immersion treatment at 40 °C maintained its wrinkled structure in phosphate-buffered saline even after five days, although the wrinkles were broadened by hydration of the skin layer. Interestingly, higher cell numbers were observed in the 3T3 cell culture using the wrinkled film than using flat film with the same surface composition. In addition, the high biocompatibility of the wrinkled film was confirmed by in vivo experiments. These results strongly encourage application of the wrinkled film as a mechano-structural cue. Studies of the advanced applications for the wrinkled films are now in progress. Full article

This work describes the synthesis of silica microspheres using sodium silicate obtained as a byproduct in the production of Egyptian Rosetta zircon concentrate. The obtained mesoporous silica microspheres were further modified with aminopropyltriethoxy silane and 2,4-Dihydroxybenzaldehyde to produce Schiff’s base silica sorbent (HB/A@Si-MNS). HB/A@Si-MNS was used for the selective extraction of hafnium from zircon mineral leach liqueur. The fabrication process and surface properties of HB/A@Si-MNS were confirmed by the means of X-ray Fluorescence (XRF), scanning electron microscop (SEM), energy depressive X-ray (EDX), Fourier-transform infrared spectroscopy (FT-IR), and elemental analysis. The uptake behavior of HB/A@Si-MNS towards Zr(IV) and Hf(IV) ions were studied under different experimental conditions. Adsorption curves indicate that the uptake of Zr(IV) and Hf(IV) on HB/A@Si-MNS is a spontaneous, endothermic monolayer system controlled by intraparticle diffusion. Elution efficiencies were found to be 94% and 98% for Zr(IV) and Hf(IV), respectively. The regenerated HB/A@SI-MNS showed uptake capacity comparable to that of fresh ones over 3 cycles. The results of the extraction of Hf(IV) than Zr(IV) from Rosetta zircon concentrate show that HB/A@SI-MNS has a preferential selectivity towards Hf(IV) than Zr(IV). Therefore, the studied material may be promising for the selective separation of Hf(IV) from Zr(IV). Full article

Crude oil asphaltenes contain a wide series of chemical species, which includes the most polar compounds and interfacially active agents from the petroleum. Asphaltenes have been considered to be implicated in foam and emulsion formation during the petroleum recovery and production process. In this work, the interfacial activity of organic solutions containing asphaltene and n-alcohols was investigated. Asphaltene extraction from a 28°API crude oil produced 2.5 wt % of n-pentane precipitated asphaltene (C5I). Dynamic surface and interfacial tensions of asphaltene solutions were assessed by the pendant drop method. Asphaltene films were evaluated at the air-water interface using a Langmuir trough. Results were expressed by means of the interfacial tension time-dependence. Interfacial tension measurements showed alcohols reduce the toluene/water interfacial tension of asphaltene solutions. The interfacial tension was reduced from 23 mN/m to 15.5 mN/m for a 2 g/L solution of asphaltene plus n-butanol. Higher asphaltene concentrations did not affect the toluene/air surface tension. The effects of n-alcohols on the asphaltene surface activity was dependent on the asphaltene aggregation state. n-Alcohols modify the asphaltene film elasticity and the film phase behavior. Full article