Anomalous Stability of Carbon Dioxide in pH-Controlled Bubble Coalescence

✍ Scribed by Dr. Rico F. Tabor; Prof. Derek Y. C. Chan; Prof. Franz Grieser; Prof. Raymond R. Dagastine

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 409 KB
• Volume: 50
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.201006552

✦ Synopsis

Gas bubbles are formed as cavities in liquids, their pressure, shape, and deformability determined by the surface tension of the liquid. They are vital components in foams, microfluidics, sonochemical reactions, generation of atmospheric aerosol, and in the scent and taste delivery of soft drinks, beers, and champagne. In all of these cases, their stability or coalescence during inter-bubble collisions is a vital factor in determining bubble behavior and lifetime. It has been noted previously that, due to its high water-solubility and unusual aqueous chemistry, carbon dioxide may be expected to behave differently than inert gases, suggesting that a comparative study is needed. Here, we explore bubble coalescence as a function of pH and gas type, demonstrating that CO 2 has a suprising and vital role, by comparing pure CO 2 bubbles with air (which has CO 2 as a minor component), argon, and nitrogen (pure, inert gases).

Recently, advances in the technique of atomic force microscopy (AFM) have allowed direct measurements of the force and coalescence behavior between pairs of bubbles and drops with diameters around 100 mm to be made. Here, for the first time we use low velocities in order to understand the equilibrium forces acting between bubbles as they approach one another, and which ultimately determine their coalescence or stability.

Bubble interaction events were measured by using an AFM cantilever to pick one bubble up in the size range 50-200 mm from a glass substrate, and drive this bubble towards a substrate-immobilized bubble at a fixed, low speed (0.2 mm s À1 , chosen to eliminate the effects of hydrodynamic drainage forces between the bubbles), until either coalescence occurred, or until a fixed deflection of the cantilever