High‐Speed 3D Imaging of Multiphase Systems: Applying SCAPE Microscopy to Analog Experiments in Volcanology and Earth Sciences

Abstract

Multiphase systems composed of gases, liquids, and solids are ubiquitous in nature and industry. Solids and gas bubbles may be suspended in a fluid, or a gas and liquid phase may be flowing through a solid porous medium. Geological processes that are characterized by multiphase systems include sedimentation, melt and magma migration, deposition and extraction of ores or fossil fuels, and sequestration of CO 2 in the subsurface. These types of multiphase flows involve complex microscale processes that have a direct impact on the macroscopic mechanical, chemical, and thermal properties of the suspension or flow. Here, we will focus on three types of small-scale multiphase interactions that have implications for large-scale natural Abstract Multiphase suspensions are complex systems where microscopic interactions between suspended bubbles, particles, and liquids can significantly alter bulk behavior. Observing the internal mechanics of such suspensions can help constrain the dynamics of natural multiphase flows. To capture these internal processes at high speed and in three dimensions, we propose the use of Swept Confocally Aligned Planar Excitation (SCAPE) microscopy in analog experiments. This imaging technique, developed for neuroscience and biology, uses a sweeping light sheet to illuminate and image fluorophores within a sample. We performed experiments using water and various oils as the liquid phases, glass or PMMA particles for solids, and air or CO 2 for gas, which we imaged at rates >50 volumes per second, over a volume size of ∼1 × 1 × 0.4 mm. We focused on three case studies: (1) bubble nucleation, growth, and rise in sparkling water, where we found that bubble detachment from angular PMMA particles left residual bubbles that also grew and detached, generating more bubbles compared to smooth particles; (2) flow of immiscible liquids (water droplets suspended in canola oil) in a porous matrix of PMMA beads, which highlighted the importance of pore and throat sizes on droplet velocities; and (3) injection of air bubbles into concentrated suspensions of glass beads or crushed PMMA particles in a refractive-index-matched liquid, which revealed particle motion and strong alterations of the bubble shape. We conclude that SCAPE microscopy is a powerful tool to study the dynamics of multiphase systems. Plain Language Summary Many natural systems are mixtures that include a solid phase, a liquid phase, and/or a volatile phase. Magmas, for example, contain solid crystals and volatile bubbles suspended in a liquid silicate melt. To explain the overall behavior of such mixtures, it is important to understand the interactions between the different phases, which often occur at the microscopic level. Here, we study these interactions in laboratory experiments where we observe liquids (oil, water), gas (CO 2 , air), and solid particles (plastic, glass) interacting. We imaged our experiments in three dimensions (3D) and at high speed (up to 50 times per second) using a technique called "SCAPE microscopy." The SCAPE micro...