Effect of surface functionalized silica nanoparticles on interfacial behavior: Wettability, interfacial tension and emulsification characteristics

Due to their unique properties, nanoparticles have recently attracted lots of attention for enhanced oil recovery (EOR) and CO2 geo-sequestration (CGS) applications. The purpose of this research is to offer a better understanding of the role of nanoparticles on interfacial phenomena with a special focus on wettability alteration, interfacial tension and emulsification characteristics. Contact angle measurements were used to explore the effect of nanoparticles on wettability alteration of glass surfaces using sessile drop method in the absence and presence of NaCl. Scanning electron microscopy (SEM) images were collected to visualize how nanoparticles change the wettability of the surfaces. The effect of different parameters on morphology variation of glass surfaces and the consequent wettability alteration was examined. The investigated variables were nanoparticle concentration, exposure time, measurement time and salinity. Next, the effect of nanoparticles on interfacial tension (IFT) between water and n-octane was studied via the Wilhelmy plate method. The effect of nanoparticle concentration on IFT was investigated with and without added NaCl. Finally, a series of simple batch experiments were conducted to observe the effect of nanoparticles in emulsification behavior of a water-n-octane system. Photography and optical microscopy images were collected to analyze the stability and morphology of the formed emulsions for different nanoparticle concentrations in the absence and presence of NaCl. Our results show that the EOR-12 nanoparticles have excellent water-wetness properties and emulsification characteristics but do not necessarily change the IFT in a water-n-octane system. micrographs taken from the nanofluid-treated glass surfaces showed a thick coverage of nanoparticles confirming the adsorption of nanoparticles onto the surface. Additionally, SEM images revealed a topography change of surfaces from smooth to rough after treatment with nanofluid which is the responsible mechanism for the observed wettability alteration. The higher the exposure time, the rougher the nanoparticle adsorption layer and consequently the better the performance of nanoparticles in wettability alteration of glass surfaces. Additionally, up to a threshold concentration, the contact angle decreased as the nanoparticle concentration increased, but above the threshold concentration, the measured contact angle did not show remarkable reduction. Conducting contact angle measurements in the presence of NaCl demonstrated that salinity can increase the adsorption rate, the final number of nanoparticles on the glass surface, the surface roughness and the intrinsic contact angle of nanoparticles leading to a better water-wetness. Testing different concentration of nanoparticles demonstrated that in the presence of NaCl, the wettability of the glass surface was not affected by the concentration and low concentrations of nanoparticles act as good as high concentrations. IFT measurements did not show any significant reduction in IFT between water and n-octane for all the tested concentrations with and without added NaCl mainly because of lack of the energy required to bring the nanoparticles at the interface. The results of batch emulsification experiments revealed that EOR-12 nanoparticles could serve as highly efficient Pickering emulsifiers in terms of both initial emulsion volume and its stability over time with and without NaCl. Adsorption of the nanoparticles at the interface was identified as the underlying mechanism for the emulsification characteristics of the nanoparticles. Photographs and optical microscopy measurement results illustrated that by tuning the nanoparticle concentration, emulsion droplet size and its uniformity can be adjusted. By utilizing higher concentrations of nanofluid, emulsions with smaller and more uniform droplet size and higher stability can be created.