Foaming and defoaming properties of CO2-switchable surfactants

The present study is about the foaming and defoaming properties of the CO2-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 CO2, C(14)DMA is a water insoluble organic molecule without any surface activity thus being unable to stabilize foams. In the presence of CO2, 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 CO2 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 CO2 is displaced by N-2 thus deprotonating and deactivating the surfactant.

Automated summary

This study focuses on the foaming and defoaming properties of the CO2-switchable surfactant N,N-dimethyltetradecylamine (C(14)DMA) and compares it with the non-switchable counterpart tetradecyltrimethylammonium bromide (C(14)TAB). The presence of CO2 allows C(14)DMA to transform into a cationic surfactant, but the foam stability differs depending on the gas. When foamed with N-2, C(14)DMA shows switchability, while C(14)TAB remains stable. This difference is attributed to the continuous switch off of surface activity in C(14)DMA due to the displacement of CO2 by N-2.