Gisle Øye

Sol-Gel Synthesis of Non-Silica Monolithic Materials

Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing materials of other oxides than silica. In this review, we present different synthesis methods for inorganic, non-silica monolithic materials. Some examples of application of the materials are also included.

Surface Characterization of Model, Outcrop, and Reservoir Samples in Low Salinity Aqueous Solutions

The purpose of this study was to characterize model, outcrop, and reservoir samples under low salinity, different cationic valency, and pH ranges. Potentiometric titrations and zeta potential measurements were performed in order to determine the surface properties at different pH. The extent of ion adsorption on the mineral surfaces was found by the difference between the two approaches. X-ray diffraction and cation exchange capacity measurements were also performed. All samples except calcite showed high, negative zeta potentials in fresh water at pH > 6, followed by NaCl, low salinity solution (LSS), and solutions with divalent cations. The effect of ion valency on the zeta potential at low pH values was not prominent. Above pH 8, H+ and OH− were not potential determining ions for samples that contained calcite and dolomite more than 1.5%. Above pH 8, the presence of carbonates in outcrop and reservoir samples significantly affected the zeta potential by reversing the charge in divalent solutions. The cation exchange capacity of predominant quartz, mixed quartz-clay-carbonate, and quartz-carbonate sandstones was 0.0, 0.2, and 2.2 meqv/100 g, respectively. The compositional differences between the samples were also reflected in the point of zero charge (pzc) values. Samples containing more than 1.5% carbonates had pzc in the range of pH 8–9, while samples with small fractions of carbonates or without carbonates had pzc values in the range of pH 2.9–3.3.

Interfacial Behavior of Naphthenic Acids and Multivalent Cations in Systems with Oil and Water. I. A Pendant Drop Study of Interactions Between n‐Dodecyl Benzoic Acid and Divalent Cations

Abstract Dynamic interfacial tension (IFT) measurements were used to investigate the interactions between a dissociated model naphthenic acid (p‐(n‐dodecyl) benzoic acid) and various divalent metallic cations (Mg2+, Ca2+, Sr2+, and Ba2+) across a toluene/hexadecane–water interface. The measurements were performed by using the pendant drop technique. The results obtained, plotted as IFT vs. time gave curves with similar shapes but different slopes and levels of the equilibrium IFT, depending upon the acid and salt concentrations and the type of cation added. Due to differences in degree of hydration of the various cations, the products of the reaction between dissociated acid monomers and the cations showed differences in solubility, which, in turn, affected the IFT. Based on the shapes of the curves, the mechanisms of the reactions involved in the process are discussed.

Rheological Properties of Aqueous Silica Particle Suspensions

The rheological properties of aqueous silica suspensions were investigated as a function of volume fraction of particles, particle size, and shear rate. Monodisperse particles of three sizes (0.1, 0.5, and 1 µm) were synthesized according to the Stöber process. In addition two fumed silica samples (Aerosil 200 and Aerosil 380) were investigated. These particles form stable agglomerates consisting of primary particles in solution. The Stöber particle suspensions showed a shear thinning behavior at volume fractions above 0.3. Furthermore, the viscosity increased with decreasing particle size. Depending on the particle size, the relative viscosity of the suspensions started to increase substantially at volume fractions between 0.3 and 0.4. Oscillation measurements confirmed a transition from liquid‐like viscoelastic suspensions to solid‐like viscoelastic suspensions in this range. The Aerosil suspensions displayed a shear thinning behavior at volume fractions above 0.04. The relative viscosity increased at this concentration as well. The differences between the Stöber particle suspensions and Aerosil suspensions were attributed to agglomeration of primary particles in the latter case. However, the relative viscosity of all the suspensions were well fitted to the Krieger and Dougherty model.

Rheological Properties of Silica Particle Suspensions in Mineral Oil

The rheological properties of particles suspended in a non‐polar mineral oil have been investigated as a function of volume fraction of particles, particle size, surface properties and shear rate. Three different types of particles were investigated; glass microspheres, monodisperse silica particles and fumed silica. The suspensions showed shear thinning behavior at higher volume fractions, and the viscosity increased with decreasing particle size. The hydrophobic particles display lass shear thinning effects. The relative viscosity of all the suspensions was well fitted to the Krieger and Dougherty model.

Novel Surfaces with Applicability for Preventing Wax Deposition: A Review

Paraffin wax deposition is a ubiquitous phenomenon in the petroleum production industry. Many types of internal pipe coating materials have previously been tested for preventing wax deposition, but none have demonstrated successful performance. It has become increasingly evident that an improved knowledge of the chemistry and physics of wax deposition will be required in order to develop new wax-repellent materials. In particular, it is important to understand the mechanisms used to inhibit similar deposition problems in outside industries. In order to achieve these objectives, a state-of-the-art literature survey was performed to identify the role and function of nonstick and anti-adhesive surfaces in the food, paint, marine, automotive, biomedical, tribological, optical, and petroleum industries. Information was derived from academic, industrial, and intellectual property sources. This review presents a comprehensive compilation of materials and surface modification techniques that show potential for inhibiting or eliminating paraffin wax deposition. A wide variety of metal surface treatments and synthesized polymers are discussed. It is established that nanotechnology surfaces based on fabricated microstructures are inapplicable for use in preventing solid-liquid deposition. On the other hand, self-assembled polymers and nanocomposite materials exhibiting smooth surfaces and low surface free energies may provide appropriate surface technologies for prevention of wax deposition. Based on current adhesion theory postulations, as well as analogies to similar deposition processes, promising new material classes include fluoro-siloxanes, fluoro-urethanes, oxazolane-based polymers, and DLC-polymer hybrids.

Rheological Properties of Particle-Stabilized Emulsions

We have studied the rheological properties of fumed silica particle-stabilized emulsions. Two particles of different polarity were considered, the first more hydrophilic “Aerosil R7200,” the second more hydrophobic “Aerosil R972.” These particles flocculate and probably form a network at the investigated concentration. The flow curves of emulsions stabilized by a single type of particles exhibit yield stress, shear-thinning behavior and thixotropy. Moreover they display rheological features typical of gels. These features are attributed to strengthening of the particle network by droplets. Moreover the rheological properties of w/o emulsions stabilized by hydrophobic are similar to the ones of o/w emulsions stabilized by hydrophilic particles. The rheological properties of o/w emulsions stabilized by mixtures of hydrophilic and hydrophobic particles have then been studied by keeping the total particle concentration constant and varying the mass ratio between particles. The results show that when the hydrophobic particle concentration increases, the viscosity and stability of emulsions decrease establishing evidence that the network is weakened due to preferential orientation of hydrophobic particles towards the oil phase.

Effect of pH and Salt on Rheological Properties of Aerosil Suspensions

Ionic strength and pH will influence the zeta potential of suspended particles, and consequently particle interactions and rheological properties as well. In this study the rheological properties and aggregation behaviour of Aerosil particles dispersed in aqueous solutions with various pH and salt concentration were studied. The potential energy was estimated by the DLVO theory and short range hydration forces and compared to the experimentally determined zeta potential. The strongest attraction between particles occurs at the isoelectric point (pH 4) and resulted in large aggregates, which gave relatively higher values of viscosity, yield stress, moduli, and shear thinning effects. The relative viscosity as a function of volume fraction was fitted to the Krieger and Dougherty model for all the suspensions. Oscillation measurements showed that the suspensions display elastic behaviour at low pH and viscous behavior at high pH. Furthermore, suspensions with high salt content had higher storage moduli. A power law dependency of storage moduli with volume fraction could be used to indicate the interaction strength between particles.

Desorption of Asphaltenes from Silica-Coated Quartz Crystal Surfaces in Low Saline Aqueous Solutions

The quartz crystal microbalance (QCM) was used to study desorption of asphaltenes from silica-coated quartz crystals upon exposure to various aqueous low saline solutions of different salt concentrations and cationic valency. Ultraviolet (UV) spectroscopy measurements confirmed desorption in selected experiments. The amount of desorption was related to the type and concentration of electrolyte and the sequence of injecting the electrolyte solutions. Initial desorption upon exposure to solutions with high ionic strength was likely due to repulsion between negatively charged sites acquired at the silica and the asphaltenes. During the injection of low saline aqueous solutions, a critical expansion of the diffuse double layer was required for desorption to occur. Comparatively lower desorption of asphaltenes was observed in the CaCl2 solutions than in NaCl and seawater solutions.

Interfacial Tension Measurements Between Oil Fractions of a Crude Oil and Aqueous Solutions with Different Ionic Composition and pH

Dynamic and equilibrium interfacial tensions between crude oil fractions and aqueous solutions of various compositions and pH were measured. The basic oil components seemed to determine the interfacial tensions at pH 2, while the non-dissociated and dissociated acidic components governed the interfacial tension at the natural pH and pH 9, respectively. The ionic composition of the aqueous phase influenced the degree of dissociation of the acidic components at pH 9: Na+ ions in the aqueous phase promoted dissociation of the interfacial acidic components (compared to pure water), while Ca2+ ions resulted in complexation with the dissociated acids and most likely formation of stable interfacial films. The amount of Ca2+ determined which of these phenomena that dominated when both ions were present in sea water solutions. Generally, the interfacial tensions of the oil fractions were lower when measured against the high salinity aqueous solutions than against the corresponding low salinity solutions.