Foaming and defoaming properties of CO₂‐switchable surfactants

Abstract

The present study is about the foaming and defoaming properties of the CO2‐switchable surfactant N,N‐dimethyltetradecylamine (C14DMA) and its advantages compared with the non‐switchable counterpart tetradecyltrimethylammonium bromide (C14TAB). In the absence of CO2, C14DMA 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 C14DMA and C14TAB 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 N2 reveals the switchability of C14DMA: while the volume of foams stabilized with C14TAB hardly changes over 1600 s, the volume of foams stabilized with C14DMA 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 C14DMA is continuously switching off since CO2 is displaced by N2 thus deprotonating and deactivating the surfactant.

Influence of a CO2-switchable additive on the surface and foaming properties of a cationic non-switchable surfactant

“…However, conductivity measurements in the bulk phase of aqueous solutions containing CO 2 -switchable species show that the protonation step is faster than the deprotonation step. 5,7,26 We thus argue that even small amounts of neutral TMBDA are capable of destabilizing foams. Consequently, a very high % protonation is needed to achieve foam stability and even medium % protonation is insufficient.…”

“…This is in line with the observations Poole et al made for foaming C 14 TAB solutions with N 2 and CO 2 . 7 As CO 2 is a much more water soluble gas than N 2 , its usage significantly accelerates coarsening, which drastically speeds up foam decay. 23,25 3.2.2 Influence of the additive and switching on foamability and foam stability.…”

“…While significant work on the use of CO 2 -switchable surfactants for foam stabilization has been reported, [4][5][6][7] the possibility of achieving CO 2 -switchable foam stability using non-switchable surfactants is appealing because such surfactants are cheaper and already available in large quantities. The core technology that makes this possible is Switchable Water (SW), meaning aqueous solutions of CO 2 -switchable properties.…”

Colloids with reversible stability switched by tris[2‐(dimethylamino)ethyl]amine

“…CO 2 has been effectively utilized for intelligent control of colloidal properties, owing to its cost‐effectiveness and environmental‐friendly nature, as reported in previous studies (Jiang et al, 2013; Li et al, 2016; Lin & Theato, 2013; Liu et al, 2006). The substance serves as a trigger in this context (Benedix, Botsch, et al, 2023; Benedix, Poole, et al, 2023; Elhag et al, 2018; Jessop et al, 2005; Poole et al, 2022; Umlong & Ismail, 2005). The utilization of CO 2 switchable compounds is a frequently employed method for the reversible modification of emulsion and latex stability.…”