A systematic approach to alkaline-surfactant-foam flooding of heavy oil: microfluidic assessment with a novel phase-behavior viscosity map

The apparent viscosity of viscous heavy oil emulsions in water can be less than that of the bulk oil. Microfluidic flooding experiments were conducted to evaluate how alkali-surfactant-foam enhanced oil recovery (ASF EOR) of heavy oil is affected by emulsion formation. A novel phase-behavior viscosity map-a plot of added salinity vs. soap fraction combining phase behavior and bulk apparent viscosity information-is proposed as a rapid and convenient method for identifying suitable injection compositions. The characteristic soap fraction, [Formula: see text], is shown to be an effective benchmark for relating information from the phase-viscosity map to expected ASF flood test performance in micromodels. Characteristically more hydrophilic cases were found to be favorable for recovering oil, despite greater interfacial tensions, due to wettability alteration towards water-wet conditions and the formation of low apparent-viscosity oil-in-water (O/W) macroemulsions. Wettability alteration and bubble-oil pinch-off were identified as contributing mechanisms to the formation of these macroemulsions. Conversely, characteristically less hydrophilic cases were accompanied by a large increase in apparent viscosity due to the formation of water-in-oil (W/O) macroemulsions.

Isolation and mutational assessment of pancreatic cancer extracellular vesicles using a microfluidic platform

Cancer cells release extracellular vesicles known as extracellular vesicles (EVs), containing tumor-derived DNA, RNA and proteins within their cargo, into the circulation. Circulating tumor-derived extracellular vesicles (TEV) can be used in the context of serial "liquid biopsies" for early detection of cancer, for monitoring disease burden in patients, and for assessing recurrence in the post-resection setting. Nonetheless, isolating sufficient TEV by ultracentrifugation-based approaches, in order to enable molecular assessment of EVs cargo, can be an arduous, time-consuming process and is inconsistent in the context of yield and purity among institutions. Herein, we describe a microfluidic platform, which we have named MITEV (Microfluidic Isolation of Tumor-derived Extracellular Vesicles) for the rapid isolation of TEV from the plasma of pancreatic cancer patients. The device, which has ~100,000 pillars placed in a zigzag pattern and is coated with antibodies against generic EV surface proteins (anti-CD63, -CD9, and -CD81 antibodies) or the TEV specific anti-Epithelial Cell Adhesion Molecule (EpCAM) antibody, is capable of high-throughput EVs isolation and yields sufficient DNA (total of ~2-14 ng from 2-ml plasma) for downstream genomic analysis. Using two independent quantitative platforms, droplet digital polymerase chain reaction (ddPCR) and molecular barcoding using nanoString nCounter® technology, we can reliably identify KRAS mutations within isolated TEV of treatment-naïve metastatic pancreatic cancer patients. Our study suggests that the MITEV device can be used for point-of-care applications, such as in the context of monitoring residual or recurrent tumor presence in pancreatic cancer patients undergoing therapy.

Evaluating physicochemical properties of crude oil as indicators of low-salinity-induced wettability alteration in carbonate minerals

The injection of low-salinity brine enhances oil recovery by altering the mineral wettability in carbonate reservoirs. However, the reported effectiveness of low-salinity water varies significantly in the literature, and the underlying mechanism of wettability alteration is controversial. In this work, we investigate the relationships between characteristics of crude oils and the oils’ response to low-salinity water in a spontaneous imbibition test, aiming (1) to identify suitable indicators of the effectiveness of low-salinity water and (2) to evaluate possible mechanisms of low-salinity–induced wettability alteration, including rock/oil charge repulsion and microdispersion formation. Seven oils are tested by spontaneous imbibition and fully characterized in terms of their acidity, zeta potential, interfacial tension, microdispersion propensity, water-soluble organics content and saturate-aromatic-resin-asphaltene fractionation. For the first time, the effectiveness of low-salinity water is found to positively correlate with the oil interfacial tension in low-salinity water. Oils with higher interfacial activity are found to respond more positively to low-salinity water. Moreover, cryogenic transmission electron microscopy images suggest that microdispersion is essentially macroemulsion, and its formation is an effective indicator – but not the root cause – of wettability alteration. The repulsive zeta potential for the rock and the oil in low-salinity water is found to be an insufficient condition for wettability alteration in carbonate minerals.

Destabilization, Propagation, and Generation of Surfactant-Stabilized Foam during Crude Oil Displacement in Heterogeneous Model Porous Media

Foam flooding in porous media is of increasing interest due to its numerous applications such as enhanced oil recovery, aquifer remediation, and hydraulic fracturing. However, the mechanisms of oil-foam interactions have yet to be fully understood at the pore level. Here, we present three characteristic zones identified in experiments involving the displacement of crude oil from model porous media via surfactant-stabilized foam, and we describe a series of pore-level dynamics in these zones which were not observed in experiments involving paraffin oil. In the displacement front zone, foam coalesces upon initial contact with crude oil, which is known to destabilize the liquid lamellae of the foam. Directly upstream, a transition zone occurs where surface wettability is altered from oil-wet to water-wet. After this transition takes place, a strong foam bank zone exists where foam is generated within the porous media. We visualized each zone using a microfluidic platform, and we discuss the unique physicochemical phenomena that define each zone. In our analysis, we also provide an updated mechanistic understanding of the "smart rheology" of foam which builds upon simple "phase separation" observations in the literature.

Microfluidic Devices for Characterizing Pore-scale Event Processes in Porous Media for Oil Recovery Applications

Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are resistant to low molecular-weight oil components, unlike traditional polydimethylsiloxane (PDMS) devices. Here, we demonstrate a facile method for making a device with this property, and we use the product of this protocol for examining the pore-scale mechanisms by which foam recovers crude oil. A pattern is first designed using computer-aided design (CAD) software and printed on a transparency with a high-resolution printer. This pattern is then transferred to a photoresist via a lithography procedure. PDMS is cast on the pattern, cured in an oven, and removed to obtain a mold. A thiol-ene crosslinking polymer, commonly used as an optical adhesive (OA), is then poured onto the mold and cured under UV light. The PDMS mold is peeled away from the optical adhesive cast. A glass substrate is then prepared, and the two halves of the device are bonded together. Optical adhesive-based devices are more robust than traditional PDMS microfluidic devices. The epoxy structure is resistant to swelling by many organic solvents, which opens new possibilities for experiments involving light organic liquids. Additionally, the surface wettability behavior of these devices is more stable than that of PDMS. The construction of optical adhesive microfluidic devices is simple, yet requires incrementally more effort than the making of PDMS-based devices. Also, though optical adhesive devices are stable in organic liquids, they may exhibit reduced bond-strength after a long time. Optical adhesive microfluidic devices can be made in geometries that act as 2-D micromodels for porous media. These devices are applied in the study of oil displacement to improve our understanding of the pore-scale mechanisms involved in enhanced oil recovery and aquifer remediation.

Role of Gas Type on Foam Transport in Porous Media

We present the results of an experimental investigation of the effect of gas type and composition on foam transport in porous media. Steady-state foam strengths with respect to three cases of distinct gases and two cases containing binary mixtures of these gases were compared. The effects of gas solubility, the stability of lamellae, and the gas diffusion rate across the lamellae were examined. Our experimental results showed that the steady-state foam strength is inversely correlated with the gas permeability across a liquid lamella, a parameter that characterizes the rate of mass transport. The results are also in good agreement with existing observations that the foam strength for a mixture of gases is correlated with the less soluble component. Three hypotheses with different predictions of the underlying mechanism that explain the role of gas type and composition in foam strength are discussed in detail.

Evaporative assembly of MEH-PPV rings using mixed solvents at the air/water interface

Controlling the morphology of conjugated polymers has recently attracted considerable attention because of their applications in photovoltaic (PV) devices and organic light-emitting diodes (OLEDs). Here, we describe the self-assembly of a common conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), into ringlike structures via solvent evaporation on an air/water interface. The films are monitored using Brewster angle microscopy (BAM) and transferred onto a solid substrate by either the Langmuir-Blodgett (LB) or the Langmuir-Schaefer (LS) method and further characterized by atomic force microscopy (AFM). The morphology of the MEH-PPV thin film at the air/water interface can be controlled by the spreading solvent. By mixing solvents of varying spreading coefficients and evaporation rates, such as chloroform and chlorobenzene, MEH-PPV can be assembled into micrometer-sized ring structures. The optical properties of these MEH-PPV ring structures are also characterized. Lastly, MEH-PPV can be used as a soft template to organize microscale structures of nanoparticles.

Monitoring DNA binding to Escherichia coli lactose repressor using quartz crystal microbalance with dissipation

Lactose repressor protein (LacI) functions as a negative transcription regulator in Escherichia coli by binding to the operator DNA sequence. Our understanding of the immobilized LacI function and the effect of ligand binding on the conformation of LacI-DNA complexes remains poorly understood. Here, we have examined the difference in functionality of wild-type and mutant LacI binding to the target DNA using quartz crystal microbalance with dissipation (QCM-D). To direct the orientation of LacI binding to the gold surface, residue 334 was substituted with cysteine (T334C) to generate a sulfur-gold linkage. Position 334 is located on the surface opposite the DNA-binding domain and remote from the site for inducer binding. With T334C immobilized on the gold surface, our sensors successfully detect operator binding as well as the release of the operator DNA from the repressor in the presence of inducer isopropyl-β-D-thiogalactoside (IPTG). Besides the natural operator DNA sequence (O(1)), a symmetric high-affinity DNA sequence (O(sym)), and a non-specific DNA (O(ns)) sequence with low affinity were also used. In addition, the impact of anti-inducer o-nitrophenyl-beta-d-fucoside (ONPF), which stabilizes LacI operator binding, was examined. The results from immobilized mutant LacI are in good agreement with known solution parameters for LacI-ligand interactions, demonstrating that QCM-D provides a rapid and efficient measurement of DNA binding and impact of ligands upon binding for this complex oligomeric protein.

Probing the stability of magnetically assembled DNA-linked colloidal chains

The self-assembly of colloidal particles using DNA linker molecules has led to novel colloidal materials. This article describes the development and characterization of a new class of colloidal structures based on the directed assembly of DNA-linked paramagnetic particles. A key obstacle to assembling these structures is understanding the fundamental chemistry and physics of the assembly processes. The stability of these cross-linked chain structures is the first step toward reliable assembly and thus important for its applications; however, chain stability has yet to be systematically studied. In this paper, we investigate both theoretically and experimentally, the stability of DNA-linked paramagnetic colloidal chains as a function of externally applied magnetic field strength and surface grafted DNA length and density. A total interparticle free energy potential model is developed accounting for all major forces contributing to chain stability, and a phase diagram is obtained from experiments to illustrate linked chain phases, unstable unlinked particle phases, and their transitions, which agree well with those predicted by the model. From this study, optimized parameters for successful linking and building stable linked chains are obtained.