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In the present research, the adsorption of naphthenic acids from n-dodecane solutions onto hydrophilic surfaces of the most common minerals in petroleum reservoirs (silica, alumina, and calcite) has been investigated using the quartz crystal microbalance with dissipation monitoring (QCM-D). The wettability and surface roughness of the mineral surfaces applied for the QCM-D measurements were determined with contact angle and atomic force microscopy (AFM) measurements. Corrections for changes in bulk density and viscosity of the naphthenic acids solutions as a function of concentration are necessary to determine the actual adsorption levels for the QCM-D measurements and have been accounted for in the adsorption calculations. The adsorption affinity of the naphthenic acids to the mineral surfaces is ranked as calcite > alumina > silica. The adsorption data for all systems can be adequately well described by the Langmuir isotherm and adsorption free energies (ΔG°) calculated from the fitted Langmuir isotherms indicate that the binding between naphthenic acids and mineral surfaces is of a physical nature. Plots of change in surface area per molecule (σ) as a function of the variation of concentration indicate that the adsorption process of the naphthenic acids changes as a function of surface coverage and suggest that the naphthenic acids chains undergo conformational alterations during the adsorption. The surface area per molecule (σ) of the adsorbed naphthenic acids onto the mineral surfaces is calcite < alumina < silica for all concentrations, which supports the adsorption affinity ranking.

The effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material.The magnitudes of the particle-particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl 2 ). As expected, the energies of particle-particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces.The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation.Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.

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The time dependence of the interfacial tension between water-acidic crude oil and watersynthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20 C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.

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