Foaming and defoaming properties of CO2‐switchable surfactants

Abstract The present study is about the foaming and defoaming properties of the CO 2 ‐switchable surfactant N,N‐dimethyltetradecylamine (C 14 DMA) and its advantages compared with the non‐switchable counterpart tetradecyltrimethylammonium bromide (C 14 TAB). In the absence of CO 2 , C 14 DMA is a water insoluble organic molecule without any surface activity thus being unable to stabilize foams. In the presence of CO 2 , the head group becomes protonated which transforms the water insoluble molecule into a cationic surfactant. Comparing the surface properties and foamability of C 14 DMA and C 14 TAB one finds a very similar behavior. However, the foam stabilities differ depending on the gas. Foaming the two‐surfactant solutions with CO 2 leads to very unstable foams in both cases. However, foaming the two surfactant solutions with N 2 reveals the switchability of C 14 DMA: while the volume of foams stabilized with C 14 TAB hardly changes over 1600 s, the volume of foams stabilized with C 14 DMA decreases significantly in the same period of time. This difference is due to the fact that the surface activity, that is, the amphiphilic nature, of C 14 DMA is continuously switching off since CO 2 is displaced by N 2 thus deprotonating and deactivating the surfactant.