Temperature dependence of diffusiophoresis a novel microfluidic approach.

The temperature dependence of the diffusiophoretic mobility () is investigated experimentally and compared with theoretical predictions. These systematic measurements were made possible by a new microfluidic approach that enables truly steady state gradients to be imposed, and direct and repeatable measurements of diffusiophoretic migration to be made over hours-long time scales. Diffusiophoretic mobilities were measured for fluorescent, negatively charged polystyrene particles under NaCl gradients, at temperatures ranging from 20 °C to 70 °C.

A two-step strategy for delivering particles to targets hidden within microfabricated porous media.

The delivery of small particles into porous environments remains highly challenging because of the low permeability to the fluids that carry these colloids. Even more challenging is that the specific location of targets in the porous environment usually is not known and cannot be determined from the outside. Here, we demonstrate a two-step strategy to deliver suspended colloids to targets that are "hidden" within closed porous media.

High-temperature high-pressure microfluidic system for rapid screening of supercritical CO foaming agents.

CO foam helps to increase the viscosity of CO flood fluid and thus improve the process efficiency of the anthropogenic greenhouse gas's subsurface utilization and sequestration. Successful CO foam formation mandates the development of high-performance chemicals at close to reservoir conditions, which in turn requires extensive laboratory tests and evaluations. This work demonstrates the utilization of a microfluidic reservoir analogue for rapid evaluation and screening of commercial surfactants (i.

Interaction of Stabilized Alkylbenzene Sulfonate Surfactants on the Nanoscale with Water-Wet and Oil-Wet Carbonate Surfaces under High-Salinity and High-Temperature Conditions: A QCM-D Study.

Understanding the interactions of surfactants and wettability alteration of surfaces is important for many fields, including oil and gas recovery. This work utilizes the quartz crystal microbalance with dissipation to study the interaction of stabilized linear and branched alkylbenzene sulfonates (ABSs), among the most cost-efficient industrial surfactants, with water- and oil-wet calcite surfaces under high-salinity and high-temperature conditions. Confocal laser scanning microscopy is also used to study the effect of the type of ABS on their interaction with oil-wet calcite surfaces.

Toward Reservoir-on-a-Chip: Rapid Performance Evaluation of Enhanced Oil Recovery Surfactants for Carbonate Reservoirs Using a Calcite-Coated Micromodel.

Enhanced oil recovery (EOR) plays a significant role in improving oil production. Tertiary EOR, including surfactant flooding, can potentially mobilize residual oil after water flooding. Prior to the field deployment, the surfactant performance must be evaluated using site-specific crude oil at reservoir conditions.

Molecular Assembly of Surfactant Mixtures in Oil-Swollen Micelles: Implications for High Salinity Colloidal Stability.

Alkylbenzene sulfonates are one of the most important synthetic surfactant families, considering their wide applicability, cost-effectiveness, and overall consumption levels. Nevertheless, their low salt tolerance (especially divalent ion contents) prevented their wider applications such as enhanced oil recovery in high salinity reservoirs. Here, using experiments and atomistic molecular dynamics simulations, we demonstrated that the high salinity colloidal stability of alkylbenzene sulfonates can be dramatically increased by mixing with zwitterionic cosurfactants in oil-swollen micelles.

Diffusiophoretic Focusing of Suspended Colloids.

Using a microfluidic system to impose and maintain controlled, steady-state multicomponent pH and electrolyte gradients, we present systems where the diffusiophoretic migration of suspended colloids leads them to focus at a particular position, even in steady-state gradients. We show that naively superpositing effects of each gradient may seem conceptually and qualitatively reasonable, yet is invalid due to the coupled transport of these multicomponent electrolytes. In fact, reformulating the classic theories in terms of the flux of each species (rather than local gradients) reveals rather stringent conditions that are necessary for diffusiophoretic focusing in steady gradients.

Direct Measurements of Colloidal Solvophoresis under Imposed Solvent and Solute Gradients.

We describe a microfluidic system that enables direct visualization and measurement of diffusiophoretic migration of colloids in response to imposed solution gradients. Such measurements have proven difficult or impossible in macroscopic systems due to difficulties in establishing solution gradients that are sufficiently strong yet hydrodynamically stable. We validate the system with measurements of the concentration-dependent diffusiophoretic mobility of polystyrene colloids in NaCl gradients, confirming that diffusiophoretic migration velocities are proportional to gradients in the logarithm of electrolyte concentration.

Dispersion stability and electrokinetic properties of intrinsic plutonium colloids: implications for subsurface transport.

Subsurface transport of plutonium (Pu) may be facilitated by the formation of intrinsic Pu colloids. While this colloid-facilitated transport is largely governed by the electrokinetic properties and dispersion stability (resistance to aggregation) of the colloids, reported experimental data is scarce. Here, we quantify the dependence of ζ-potential of intrinsic Pu(IV) colloids on pH and their aggregation rate on ionic strength.

Clay particles destabilize engineered nanoparticles in aqueous environments.

Given the ubiquity of natural clay minerals, the most likely interaction of nanoparticles released into an aquatic environment will be with suspended clay minerals. Thus, the transport of engineered nanoparticles in the subsurface and the water column will most likely be altered by their interaction with these minerals. We studied the interactions of two of the most produced nanoparticles, Ag and TiO(2), and montmorillonite to determine how heteroaggregation can alter the stability of nanoparticle/clay mineral mixtures.

Uranium-series constraints on radionuclide transport and groundwater flow at the Nopal I uranium deposit, Sierra Pena Blanca, Mexico.

Uranium-series data for groundwater samples from the Nopal I uranium ore deposit were obtained to place constraints on radionuclide transport and hydrologic processes for a nuclear waste repository located in fractured, unsaturated volcanic tuff. Decreasing uranium concentrations for wells drilled in 2003 are consistent with a simple physical mixing model that indicates that groundwater velocities are low ( approximately 10 m/y). Uranium isotopic constraints, well productivities, and radon systematics also suggest limited groundwater mixing and slow flow in the saturated zone.

Mobilization of colloidal particles by low-frequency dynamic stress stimulation.

Naturally occurring seismic events and artificially generated low-frequency (1 to 500 Hz) elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of surface and well water. The decreases in production are of particular concern, especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown.

On visualization of sub-micron particles with dark-field light microscopy.

Dark-field light microscopy is widely employed to visualize colloidal particles much smaller than the light wavelength used. In the captured images, the colloidal particles appear, against a dark background, as bright "specks" much larger than the geometrical size of the particles. To verify whether the "specks" are for individual particles or clusters of particles, experiments are performed which used low bulk concentrations of five suspensions of monodispersed particles (approximately 0.

Automated video microscopic imaging and data acquisition system for colloid deposition measurements.

An optical video microscopic system and image processing and data extraction and manipulation routines are developed for in situ detailed quantification of the deposition of colloids onto an arbitrary surface and determining their concentration distribution across the bulk suspension. The system produces a relatively large field of view (approximately 330 x 245 microm) and utilizes dark-field light microscopy to visualize colloids as small as approximately 0.3 microm in diameter at the surface and in the bulk suspension with a sufficient resolution (approximately 0.