Microfluidics investigation of the effect of bulk nanobubbles on surfactant-stabilised foams

In aqueous foams, the bubble size usually spans from tens of microns to centimetres. However, it is possible to create much smaller and stable bubbles in solutions: nanobubbles have diameters well below a micron. Many issues are still pending on nanobubbles, especially regarding their stability. Here, we address if and how the addition of nanobubbles may change the interfacial and foaming properties of surfactant solutions. Using a first microfluidic device, nanobubbles are formed within the aqueous surfactant solutions (SDS and Triton X-100 at different concentrations). A second microfluidic device then generates foams from these solutions. Additionally, we report systematic results on the interfacial and bulk properties of such solutions. Finally, we show that nanobubbles have some effects on almost all the measured quantities; however, the most striking one is enhancing the foaming of the solutions with an initial poor foamability. These measurements provide us with a comprehensive set of new results allowing us to draw a first multi-scale picture of how far nanobubbles could potentially act as foam boosters and stabilizers or be implemented in colloidal formulations. Yet, more investigations are required to unravel the mechanisms leading to our results.