Temperature-controlled ‘breathing’ of carbon dioxide bubbles

We report a microfluidic (MF) approach to studies of temperature mediated carbon dioxide (CO₂) transfer between the gas and the liquid phases. Micrometre-diameter CO₂ bubbles with a narrow size distribution were generated in an aqueous or organic liquid and subsequently were subjected to temperature changes in the downstream channel. In response to the cooling-heating-cooling cycle the bubbles underwent corresponding contraction-expansion-contraction transitions, which we term ‘bubble breathing’. We examined temperature-controlled dissolution of CO₂ in four exemplary liquid systems: deionized water, a 0.7 M aqueous solution of NaCl, ocean water extracted from Bermuda coastal waters, and dimethyl ether of poly(ethylene glycol), a solvent used in industry for absorption of CO₂. The MF approach can be extended to studies of other gases with a distinct, temperature-dependent solubility in liquids.