Hydrodynamic Signatures of Nanoparticle-Laden Oil-Water-Solid Interfaces

This research scrutinizes a multidisciplinary subject focusing on the in-situ formation of materials at oil-water interfaces and their effects on dynamics of liquid-liquid and liquid-solid interfaces. In particular, the formation of emulsions at oil-water interfaces is investigated in the presence of silica nanoparticles in the water and sorbitan monooleate surfactants in the oil. Then, the influence of in-situ generated emulsions on dynamics of (i) double emulsion/bicontinuous phase formation, (ii) drop pinch-off, and (iii) drop spreading are thoroughly examined. In the low viscosity oil, the spontaneous formation of multiple core-shell emulsions is reported. However, for the oils with a viscosity higher than 60 mPa.s, interconnected structures of oil and microemulsion phases are formed in a fraction of a second. The classical Plateau-Rayleigh instability in the presence of in-situ generated emulsions at the silica dispersion-high viscosity surfactant solution interfaces is revisited. The aqueous phase is injected vertically through a nozzle into a surfactant solution reservoir. The injection of DI-water generates single droplets. While in the presence of silica nanoparticles, a variety of flow morphologies from single droplets to straight liquid columns are observed. It is shown that the pinch-off of the silica nanoparticle dispersion droplet occurs in an elasto-capillary regime. The viscoelastic emulsion layer resists the capillary force and attenuates Plateau-Rayleigh instability, forming silica dispersion filaments. A scaling analysis based on the evaluation of the relative importance of the residence time to the required time for forming emulsions and the diffusion of emulsions from interface to bulk is conducted to identify required conditions for generating liquid filaments. Finally, filaments are used as inks for creating liquid letters and liquid-fluidic channels.In the last part of this dissertation, the effect of surfactants and nanoparticles on the spreading dynamics is examined. Silica nanoparticles at a concentration above 2.0 wt. % increase the early time spreading rate and the final wetted area. Increasing the surfactant concentration in the oil phase results in a plethora of wetting conditions from fully spreading to non-sticking. In the non-wetting system, the droplet levitates on a layer of oil which is used as a transport vehicle for depositing interfacial nanodroplets

Dynamics of Oil Dewetting and Two Phase Flow in Microchannels

The motion of three-phase contact lines (TPC), wetting dynamics, and fluid displacements in porous media have a wide range of engineering applications from coating and printing to agriculture, and subsurface flows. This dissertation investigates the early time dynamics of TPC and fluid movements in micro-channels related to subsurface oil recovery mechanisms. First, the role of the surrounding fluid viscosity on wetting dynamics is investigated. Experiments are designed to visualize the spreading of an aqueous phase droplet on a glass substrate submerged in an oil phase. Experiments reveal that the TPC velocity is a decreasing function of ambient phase viscosity which is found, through a scaling analysis, to depend on both the spreading radius and the geometric mean of drop and ambient fluids’ viscosities. Second, the effect of surfactants (sodium dodecyl sulfate: SDS) on the TPC dynamics is studied. In contrast to the dominance of viscous regime in pure water droplet spreading, two distinct early-time regimes are identified. The early time spreading dynamics, for the case of SDS added droplet, is characterized by the time exponents close to 0.5 and 1 before transitioning into the Tanner’s regime. Moreover, it is revealed that the SDS concentration has a non-monotonic effect on the early time dynamics. Increasing the SDS concentration initially retards the expansion of wetted area while accelerates the TPC velocity in the second regime. Finally, the displacement of a viscous oil by an aqueous solution in a network of micro-capillaries is investigated. The effects of silica nanoparticles and various types of surfactants on the fluid-fluid interface evolutions and the heavy oil recovery are characterized using the microfluidic approach and 3D confocal imaging. Addition of untreated silica particles enhances the oil displacement efficiency by decreasing the thickness of the remaining oil film. In the presence of surfactants, the oil phase is divided into many smaller clusters that easily flow through the channels and enhances the rate of oil recovery. Ultimately, the presence of both silica and surfactants yields to the highest level of oil recovery as a result of coupled oil phase breakup and film thickness reduction effects

Spongy all-in-liquid materials by in-situ formation of emulsions at oil-water interfaces

All-in-liquid printing promises applications from energy storage to drug delivery and tissue engineering. Here, authors present the in-situ generation of layered emulsion in a fraction of a second at the oil-water interface forming 3D tube-like structures in a liquid medium

Hydrodynamic interactions between rough surfaces

In the study of particle suspensions, away from the jamming threshold, it is common to interpret the effective viscosity in terms of the volume fraction, neglecting roughness effects. Here we show that particle roughness can significantly modify viscous dissipation in configurations that represent fixed volume-fraction conditions. We derive a hydrodynamic model for the forced interaction of a two-dimensional particle, where roughness is represented by a periodic corrugation, with an adjacent wall. In particular, we address the limit of small nominal particle-wall separation, with the corrugation amplitude comparable with said separation. A lubrication analysis provides the rectilinear and angular velocities of the particle as functions of the instantaneous angular configuration. The particle may either translate while rotating or become “locked” in a specific phase and translate without rotation. The time-averaged rectilinear velocity, which is the object of interest, is a purely geometric quantity, obtained without the need to address any time dynamics