Lab on a chip for a low-carbon future.

Transitioning our society to a sustainable future, with low or net-zero carbon emissions to the atmosphere, will require a wide-spread transformation of energy and environmental technologies. In this perspective article, we describe how lab-on-a-chip (LoC) systems can help address this challenge by providing insight into the fundamental physical and geochemical processes underlying new technologies critical to this transition, and developing the new processes and materials required. We focus on six areas: (I) subsurface carbon sequestration, (II) subsurface hydrogen storage, (III) geothermal energy extraction, (IV) bioenergy, (V) recovering critical materials, and (VI) water filtration and remediation. We hope to engage the LoC community in the many opportunities within the transition ahead, and highlight the potential of LoC approaches to the broader community of researchers, industry experts, and policy makers working toward a low-carbon future.

Mechanisms of multiphase reactive flow using biogenically calcite-functionalized micromodels.

Dissolution of carbonate minerals in porous media is important to many instances of subsurface flow, including geological carbon dioxide (CO2) sequestration, karst formation, and crude-oil reservoir stimulation and acidizing. Of particular interest, geological CO2 storage in deep carbonate reservoirs presents a significant long-term opportunity to mitigate atmospheric carbon emissions. The reactivity of carbonate reservoirs, however, may negatively impact storage formation integrity and hence jeopardize sequestered CO2 storage security. In this work, we develop a novel biogenically calcite-functionalized microvisual device to study the fundamental pore-scale reactive transport dynamics in carbonate formations. Importantly, we discover a new microscale mechanism that dictates the overall behavior of the reactive transport phenomenon, where the reaction product, CO2, due to carbonate rock dissolution forms a separate, protective phase that engulfs the carbonate rock grain and reduces further dissolution. The presence of the separate, protective CO2 phase determines overall dissolution patterns in the storage reservoir and leads to formation of preferential leakage paths. We scale these results using nondimensional numbers to demonstrate their influence on industrial CO2 storage security, safety, and capacity.

Pillars or Pancakes? Self-Cleaning Surfaces without Coating.

Surfaces that stay clean when immersed in water are important for an enormous range of applications from ships and buildings to marine, medical, and other equipment. Up until now the main strategy for designing self-cleaning surfaces has been to combine hydrophilic/hydrophobic coatings with a high aspect ratio structuring (typically micron scale pillars) to trap a (semi)static water/air layer for drag and adhesion reduction. However, such coating and structuring can distort optical properties and get damaged in harsh environments, and contamination, i.e., particles, oil droplets, and biofouling, can get trapped and aggregate in the structure. Here we present a radically different strategy for self-cleaning surface design: We show that a surface can be made self-cleaning by structuring with a pattern of very low aspect ratio pillars ("pancakes"). Now the water is not trapped. It can flow freely around the pancakes thus creating a dynamic water layer. We have applied the new pancake design to sapphire windows and made the first surfaces that are self-cleaning through structuring alone without the application of any coating. An offshore installation has now been running continuously with structured windows for more than one year. The previous uptime for unstructured windows was 7 days.

Determination of pore-scale hydrate phase equilibria in sediments using lab-on-a-chip technology.

We present an experimental protocol for fast determination of hydrate stability in porous media for a range of pressure and temperature (P, T) conditions. Using a lab-on-a-chip approach, we gain direct optical access to dynamic pore-scale hydrate formation and dissociation events to study the hydrate phase equilibria in sediments. Optical pore-scale observations of phase behavior reproduce the theoretical hydrate stability line with methane gas and distilled water, and demonstrate the accuracy of the new method. The procedure is applicable for any kind of hydrate transitions in sediments, and may be used to map gas hydrate stability zones in nature.