Determination of Dew Point Conditions for CO₂ with Impurities Using Microfluidics

Impurities can greatly modify the phase behavior of carbon dioxide (CO₂), with significant implications on the safety and cost of transport in pipelines. In this paper we demonstrate a microfluidic approach to measure the dew point of such mixtures, specifically the point at which water in supercritical CO₂ mixtures condenses to a liquid state. The method enables direct visualization of dew formation (∼ 1–2 μm diameter droplets) at industrially relevant concentrations, pressures, and temperatures. Dew point measurements for the well-studied case of pure CO₂-water agreed well with previous theoretical and experimental data over the range of pressure (up to 13.17 MPa), temperature (up to 50 °C), and water content (down to 0.00229 mol fraction) studied. The microfluidic approach showed a nearly 3-fold reduction in error as compared to previous methods. When applied to a mixture with nitrogen (2.5%) and oxygen (5.8%) impuritiestypical of flue gas from natural gas oxy-fuel combustion processesthe measured dew point pressure increased on average 17.55 ± 5.4%, indicating a more stringent minimum pressure for pipeline transport. In addition to increased precision, the microfluidic method offers a direct measurement of dew formation, requires very small volumes (∼10 μL), and is applicable to ultralow water contents (<0.005 mol fractions), circumventing the limits of previous methods

Determination of Dew Point Conditions for CO₂ with Impurities Using Microfluidics

Impurities can greatly modify the phase behavior of carbon dioxide (CO₂), with significant implications on the safety and cost of transport in pipelines. In this paper we demonstrate a microfluidic approach to measure the dew point of such mixtures, specifically the point at which water in supercritical CO₂ mixtures condenses to a liquid state. The method enables direct visualization of dew formation (∼ 1–2 μm diameter droplets) at industrially relevant concentrations, pressures, and temperatures. Dew point measurements for the well-studied case of pure CO₂-water agreed well with previous theoretical and experimental data over the range of pressure (up to 13.17 MPa), temperature (up to 50 °C), and water content (down to 0.00229 mol fraction) studied. The microfluidic approach showed a nearly 3-fold reduction in error as compared to previous methods. When applied to a mixture with nitrogen (2.5%) and oxygen (5.8%) impuritiestypical of flue gas from natural gas oxy-fuel combustion processesthe measured dew point pressure increased on average 17.55 ± 5.4%, indicating a more stringent minimum pressure for pipeline transport. In addition to increased precision, the microfluidic method offers a direct measurement of dew formation, requires very small volumes (∼10 μL), and is applicable to ultralow water contents (<0.005 mol fractions), circumventing the limits of previous methods

Rapid Microfluidics-Based Measurement of CO₂ Diffusivity in Bitumen

In this paper, we demonstrate the first application of microfluidics to study diffusive transport in extra heavy oils, such as bitumen. A cross-channel glass microfluidic chip was used to measure the CO₂ diffusion in Athabasca bitumen. The device was initially filled with CO₂ at low pressure (<1.0 bar). A plug of bitumen was injected into the central (50 μm wide and 20 μm deep) channel and, subsequently, exposed to high-pressure CO₂ on both ends. One-dimensional oil swelling in response to CO₂ diffusion was imaged over time. A simple mathematical approach was applied to calculate the diffusion coefficient based on the oil-swelling data. Measurement results are reported here at a range of pressures (1–5 MPa) and room temperature (21 °C). The measured diffusion coefficients in this range are on the order of 10^–10 m²/s, in good agreement with the relevant published data using conventional methods. In sharp contrast to conventional methods that require hours or days and ∼0.5 L of sample, the method presented here requires ∼10 min and a 1 nL plug of sample

Bitumen–Toluene Mutual Diffusion Coefficients Using Microfluidics

In this paper, we present a microfluidic approach to measure liquid solvent diffusivity in Athabasca bitumen. The method has three distinguishing features: (a) a sharp initial condition enabled by the high wettability of the solvent; (b) one-dimensional diffusive transport (in the absence of convection) ensured by microscale confinement; and (c) visible-light-based measurement enabled by the partial transparency of the bitumen at small scales. The method is applied to measure the diffusion of toluene into bitumen by imaging transmitted light profiles over time, and relating intensities to the mass fractions. Plotting toluene mass fraction versus distance/sqrt­(time), results in a tight superposition of all curves (time-dependent mass fractions) demonstrating the diffusion dominated nature of the system and the robustness of the method. The diffusion transport equations were solved and fit to a constant diffusion coefficient as well as a variety of concentration-dependent diffusion coefficient relations found in the literature. For intermediate toluene mass fractions (0.2–0.8), a constant diffusion coefficient of 2.0 × 10^–10 m²/s provides an appropriate representation. However, at low toluene mass fractions (<0.2), significantly reduced diffusive transport is observed, and endpoint analysis indicates diffusion coefficients trending toward 4.3 × 10^–11 m²/s. At high toluene mass fractions (>0.8), the values trend toward 1.5 × 10^–10 m²/s. This microfluidic method provides an inexpensive and rapid mutual diffusion coefficient evaluation, with significantly improved spatial/composition resolution vis-à-vis competing measurement methods

Disposable Plasmonics: Rapid and Inexpensive Large Area Patterning of Plasmonic Structures with CO₂ Laser Annealing

We present a method of direct patterning of plasmonic nanofeatures on glass that is fast, scalable, tunable, and accessible to a wide range of usersa unique combination in the context of current nanofabrication options for plasmonic devices. These benefits are made possible by the localized heating and subsequent annealing of thin metal films using infrared light from a commercial CO₂ laser system. This approach results in patterning times of 30 mm²/min with an average cost of $0.10/mm². Colloidal Au nanoparticles with diameters between 15 and 40 nm can be formed on glass surfaces with <i>x</i>–<i>y</i> patterning resolutions of ∼180 μm. While the higher resolution provided by lithography is essential in many applications, in cases where the spatial patterning resolution threshold is lower, commercial CO₂ laser processing can be 30-fold faster and 400-fold less expensive

Morphological Control <i>via</i> Chemical and Shear Forces in Block Copolymer Self-Assembly in the Lab-on-Chip

We investigate the effects of variation in chemical conditions (solvent composition, water content, polymer concentration, and added salt) on the morphologies formed by PS-<i>b</i>-PAA in DMF/dioxane/water mixtures in a two-phase gas–liquid segmented microfluidic reactor. The differences in morphologies between off-chip and on-chip self-assembly and on-chip morphological trends for different chemical conditions are explained by the interplay of top-down shear effects (coalescence and breakup) and bottom-up chemical forces. Using off-chip morphology results, we construct a water content-solvent composition phase diagram showing disordered, sphere, cylinder, and vesicle regions. On-chip morphologies are found to deviate from off-chip morphologies by three identified shear-induced paths: 1) sphere-to-cylinder, and 2) sphere-to-vesicle transitions, both <i>via</i> shear-induced coalescence when initial micelle sizes are small, and 3) cylinder-to-sphere transitions <i>via</i> shear-induced breakup when initial micelle sizes are large (high capillary number conditions). These pathways contribute to the generation of large extended bilayer aggregates uniquely on-chip, at either increased polymer or salt concentrations. Collectively these results demonstrate the broad utility of top-down directed molecular self-assembly in conjunction with chemical forces to control morphology and size of polymer colloids at the nanoscale

Full Characterization of CO₂–Oil Properties On-Chip: Solubility, Diffusivity, Extraction Pressure, Miscibility, and Contact Angle

Carbon capture, storage, and utilization technologies target a reduction in net CO₂ emissions to mitigate greenhouse gas effects. The largest such projects worldwide involve storing CO₂ through enhanced oil recoverya technologically and economically feasible approach that combines both storage and oil recovery. Successful implementation relies on detailed measurements of CO₂–oil properties at relevant reservoir conditions (<i>P</i> = 2.0–13.0 MPa and <i>T</i> = 23 and 50 °C). In this paper, we demonstrate a microfluidic method to quantify the comprehensive suite of mutual properties of a CO₂ and crude oil mixture including solubility, diffusivity, extraction pressure, minimum miscibility pressure (MMP), and contact angle. The time-lapse oil swelling/extraction in response to CO₂ exposure under stepwise increasing pressure was quantified via fluorescence microscopy, using the inherent fluorescence property of the oil. The CO₂ solubilities and diffusion coefficients were determined from the swelling process with measurements in strong agreement with previous results. The CO₂–oil MMP was determined from the subsequent oil extraction process with measurements within 5% of previous values. In addition, the oil–CO₂–silicon contact angle was measured throughout the process, with contact angle increasing with pressure. In contrast with conventional methods, which require days and ∼500 mL of fluid sample, the approach here provides a comprehensive suite of measurements, 100-fold faster with less than 1 μL of sample, and an opportunity to better inform large-scale CO₂ projects

Measurement of CO₂ Diffusivity for Carbon Sequestration: A Microfluidic Approach for Reservoir-Specific Analysis

Predicting carbon dioxide (CO₂) security and capacity in sequestration requires knowledge of CO₂ diffusion into reservoir fluids. In this paper we demonstrate a microfluidic based approach to measuring the mutual diffusion coefficient of carbon dioxide in water and brine. The approach enables formation of fresh CO₂–liquid interfaces; the resulting diffusion is quantified by imaging fluorescence quenching of a pH-dependent dye, and subsequent analyses. This method was applied to study the effects of site-specific variablesCO₂ pressure and salinity levelson the diffusion coefficient. In contrast to established, macro-scale pressure–volume–temperature cell methods that require large sample volumes and testing periods of hours/days, this approach requires only microliters of sample, provides results within minutes, and isolates diffusive mass transport from convective effects. The measured diffusion coefficient of CO₂ in water was constant (1.86 [±0.26] × 10^–9 m²/s) over the range of pressures (5–50 bar) tested at 26 °C, in agreement with existing models. The effects of salinity were measured with solutions of 0–5 M NaCl, where the diffusion coefficient varied up to 3 times. These experimental data support existing theory and demonstrate the applicability of this method for reservoir-specific testing

Flow-Directed Assembly of Block Copolymer Vesicles in the Lab-on-a-Chip

We demonstrate a microfluidic approach to the production of block copolymer vesicles via flow-directed self-assembly in a segmented gas–liquid device. Chemical conditions that favor spherical micelles in the bulk are found to yield a nearly pure population of vesicles on a chipa transformation of two full morphological stepsbecause of a coalescence mechanism enabled by high shear. The production of polymeric vesicles via top-down control in a microfluidic device enables new processing routes to applications including drug delivery formulations in the lab-on-a-chip

Flow-Directed Loading of Block Copolymer Micelles with Hydrophobic Probes in a Gas–Liquid Microreactor

We investigate the loading efficiencies of two chemically distinct hydrophobic fluorescent probes, pyrene and naphthalene, for self-assembly and loading of polystyrene-<i>block</i>-poly­(acrylic acid) (PS-<i>b</i>-PAA) micelles in gas–liquid segmented microfluidic reactors under different chemical and flow conditions. On-chip loading efficiencies are compared to values obtained via off-chip dropwise water addition to a solution of copolymer and probe. On-chip, probe loading efficiencies depend strongly on the chemical probe, initial solvent, water content, and flow rate. For pyrene and naphthalene probes, maximum on-chip loading efficiencies of 73 ± 6% and 11 ± 3%, respectively, are obtained, in both cases using the more polar solvent (DMF), an intermediate water content (2 wt % above critical), and a low flow rate (∼5 μL/min); these values are compared to 81 ± 6% and 48 ± 2%, respectively, for off-chip loading. On-chip loading shows a significant improvement over the off-chip process where shear-induced formation of smaller micelles enables increased encapsulation of probe. As well, we show that on-chip loading allows off-chip release kinetics to be controlled via flow rate: compared to vehicles produced at ∼5 μL/min, pyrene release kinetics from vehicles produced at ∼50 μL/min showed a longer initial period of burst release, followed by slow release over a longer total period. These results demonstrate the necessity to match probes, solvents, and running conditions to achieve effective loading, which is essential information for further developing these on-chip platforms for manufacturing drug delivery formulations