Experimental investigation of degradation of rising oil droplets using microfluidic platform and holographic interferometry

Degradations of rising crude oil droplets in aquatic ecosystems are crucial processes that has been studied intensely after major oil spills. To-date, degradation processes (e.g. dissolution and microbial consumption) and their corresponding rates of oil droplets remains unclear due to discrepancy among studies and lack of tools. Here, we combine an ecology-on-a-Chip (eChip) microfluidic platform to establish real world hydrodynamic conditions with digital holographic interferometry to measure instantaneous 3D droplet volume change over ecologically relevant time scales (>weeks) and at individual droplet scale with nm resolutions. In each experiment, we print an array of immobilized droplets over a substrate by micro-transfer printing. The substrate is placed in an eChip and degradation as volume loss are quantified directly by interferometry. Both abiotic and biotic experiments are conducted to quantify dissolution and biodegradation directly in terms of volume loss. Results show that dissolution is a rapid process while biodegradation is a slow one. Effects of surfactants at oil-water interfaces are also investigated.