Dispersion Of Organoclay In Nonpolar Media And Pickering Emulsions Stabilized By Organoclay

Montmorillonite finds wide range of applications for its special properties:natural abundance, fine size, easy modification. The applications of montmorillonite in nonaqueous media were limited for the strong hydrophilicity. However, cation-exchange reactions with organic cationic surfactants have been exploited to render the clay mineral hydrophobic at the surface and increase the basal spacing. Organic modification of montmorillonite (organoclay) has been widely used in industrial applications such as oil-field drilling fluids, paints, lubricating greases, wastewater treatment, and composite material. Thus the modifications of clay minerals have been widely studied fundamentally and in practical applications. One of the most important properties of organoclay is the ability for swelling and thixotropic gel formation in organic media. The advantages of organoclay as flow modifiers include:low volume fractions, good thermal stability, resistant to gel-breaking effects from other chemicals. Organoclay is generally used to control the rheologic property of hydrocarbon fluids.Recently, the use of organoclay in materials science and technology has attracted considerable attention. Clay, having a large aspect ratio and size, has been recognized as potential candidates for filler materials, because it exhibits superior physical and mechanical properties when compared with the pure polymer. Organic modification of clay mineral, making it hydrophobic and compatible with polymers is necessary due to the hydrophilic nature of clay. The surface energy of clay and polymer could be reduced by organic modification. Additionally, the organic cations may contain various functional groups, which can react with the polymers and enhance the adhesion between clay particles and the matrix. Thus, it is possible to obtain nanocomposites with good dispersion quality.Oil-based drilling fluid is the mud using oil as the continuous phase. The advantages of selecting an oil-based drilling fluid include:superior hole stability, enhanced shale inhibition, excellent lubrication, high temperature stability. For these benefits, oil-based drilling fluid is a better selection for drilling in deep well, high temperature well and complex conditions. For environment protection, miner oil of lower toxic was used to replace the crude oil or diesel which contains high content of aromatic hydrocarbons, but there is a problem that the organoclay could not disperse and gelling well in miner oil. In the water-in-oil (W/O) drilling fluid, orgaoclay can be adsorbed on the interface of oil and water, improving the stability of emulsion and the viscosity of drilling fluid.In this context, we studied the dispersion of organoclay in octane in attempt to improve their stability. The rheological properties of organoclay suspensions were also investigated. The emulsion stabilized by organoclay was prepared, and the factors affecting their stability were evaluated.The present dissertation includes three topics.1. Preparation, characterization of organocaly and rheological properties of organoclay suspensionCationic surfactant dimethyldioctadecylammoniurn chloride (DODMAC1) was used as the modifier to prepare organoclay, and the product was characterized by fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM). The effects of reaction time, temperature, pH value and the amounts of organic modifier on the basal spacing and amounts of organic compounds of organoclay and the stability of organoclay suspension were investigated. The optimal reaction condition was carried at50-90℃for3h with1.0cation exchange capacity (CEC) cationic surfactant. If the amount of surfactant was increased, the thermal stability of the organoclay would decrease. When the addition of surfactant was more than1.4CEC, bilayer adsorption of surfactant would occur.When organoclay is used as thickener in nonpolar miner oil such as white oil based drilling fluid, ideal result could not be achieved. Therefore we studied the rheological properties of organoclay/white oil suspension. The viscosity of the suspension increased with the dosage of DODMAC1first, and then decreased. The suspension containing organoclay of1.0CEC exhibited the maximum stability, viscosity and share thinning property. The rheological properties of silica nanoparticles suspended in a non-polar mineral oil were also investigated. The stability, viscosity and thixotropic property of silica nanoparticles are much better than organoclay.2. Dispersion of organoclay in nonpolar mediaDispersions of particles in nonpolar media have many applications in ceramics, paints, lubricants and oil-based drilling fluid. Usually, dispersions of particles in nonpolar media are unstable, and dispersants are used to improve the stability of the dispersions. The mechanism of dispersant to improve the stability of dispersions is steric stabilization. Usually, electrostatic stabilization in nonpolar media was neglected because of the low dielectric constant. However, many recent studies have shown that electrostatic stabilization can play an important role. To improve the dispersion stability of organoclay in nonpolar media is important for improving the properties of polymer-clay nanocomposites, lubricants and oil-based drilling fluids. Thus we investigated the stabilization mechanism of organoclay in octane.The dispersion of organoclay can be improved by the addition of the nonionic surfactants sorbitan monoleate (Span80), sorbitan trioleate (Span85) and1-oleoyl-rac-glycerol and anion surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The relation between the adsorption of surfactants on organoclay particles and the stability of the dispersions was investigated. The effects of the surfactants on the basal spacing of particles, electrostatic interactions between particles and rheological properties of dispersions were also measured. Based on the decrease of the particle size and the increase of the zeta potential, the improvement of the dispersion stability could be interpreted by steric and electrostatic stabilization. This work sheds some light on the selection of dispersants for improving the dispersion stability of particles in nonpolar media.3. Pickering emulsion stabilized by organoclay Organoclay typically is used to control the rheology in oil-based drilling fluid. In drilling fluid, the organoclay could also adsorb at the surface of water droplets to stabilize the W/O emulsions and improve the viscosity of mud. The aqueous phase of mud is usually comprised of high concentration of salt, to minimize water exchange between drilling fluid and the formation being drilled. Because the wettability of organoclay and salt concentration in the aqueous phase could affect the stability of the emulsion, we investigated the effects of modifier dosage of organoclay and salt concentration in the aqueous phase on the stability of W/O emulsions stabilized by organoclay.Emulsion inversion could be induced by increasing the addition of cationic surfactant modifier, as the wettability of organoclay was changed from hydrophilicity to hydrophobicity. When the amount of surfactant was less than0.8CEC, the emulsions stabilized by organoclay were O/W. When the amount of surfactant was more than0.8CEC, W/O emulsions were prepared by the hydrophobic organoclay. If the addition of surfactant was increased further, O/W emulsions were not obtained. This may be due to the removal the free surfactant in the washing process in the preparation of organoclay and the reduction of organoclay hydrophobicity by desorption of the adsorbed bilayer surfactant in emulsification process.The addition of salt could increase the hydrophobicity of particles and decrease particle zeta potential leading particle adsorption at the oil-water interface. Salts could also flocculate the particles to form visco-elastic three-dimensional network, which enhance the creaming stability of emulsion. Here, the effect of salt concentration on the W/O emulsions stabilized by organoclay was studied. The stability of emulsions decreased with the salt concentration, and stable emulsion could not be prepared when the salt concentration was above a certain value. The emulsion prepared with organoclay of1.2CEC was more stable than organoclay of1.0CEC and0.8CEC. The desorption of cationic surfactant from organoclay was measured by Total Organic Carbon Analyzer. The amount of surfactant desorbed increased with salt concentration. The desorption of cationic surfactant modifier would increase the hydrophilicity of organoclay, which is not conductive for the formation of W/O emulsion. The reasons of the decrease of the emulsion stability caused by the addition of salt were the reduction of organoclay hydrophobicity and the desorption of cationic surfactant at high salt concentration.