A Comparative Study on CO(2)-Switchable Foams Stabilized by C(22)- or C(18)-Tailed Tertiary Amines

The CO(2) aqueous foams stabilized by bioresource-derived ultra-long chain surfactants have demonstrated considerable promising application potential owing to their remarkable longevity. Nevertheless, existing research is still inadequate to establish the relationships among surfactant architecture, environmental factors, and foam properties. Herein, two cases of ultra-long chain tertiary amines with different tail lengths, N-erucamidopropyl-N,N-dimethylamine (UC(22)AMPM) and N-oleicamidopropyl-N,N-dimethylamine (UC(18)AMPM), were employed to fabricate CO(2) foams. The effect of temperature, pressure and salinity on the properties of two foam systems (i.e., foamability and foam stability) was compared using a high-temperature, high-pressure visualization foam meter. The continuous phase viscosity and liquid content for both samples were characterized using rheometry and FoamScan. The results showed that the increased concentrations or pressure enhanced the properties of both foam samples, but the increased scope for UC(22)AMPM was more pronounced. By contrast, the foam stability for both cases was impaired with increasing salinity or temperature, but the UC(18)AMPM sample is more sensitive to temperature and salinity, indicating the salt and temperature resistance of UC(18)AMPM-CO(2) foams is weaker than those of the UC(22)AMPM counterpart. These differences are associated with the longer hydrophobic chain of UC(22)AMPM, which imparts a higher viscosity and lower surface tension to foams, resisting the adverse effects of temperature and salinity.