Effect of surfactant types on the foam stability of multiwalled carbon nanotube stabilized foam

Multiwalled Carbon nanotube (MWCNT) serves as one of emerging and attractive materials for stabilizing foams due to its small size, special surface property and rod-like structure. The combination of MWCNT and surfactant has been regarded as an effective strategy to improve foam stability in porous media. However, the effects of surfactant types on the dispersity of MWCNT and on the stability of MWCNT stabilized foams have yet to be clearly understood. More importantly, the lack of comprehensive study of the synergistic interactions between surfactants and MWCNTs seriously limits the understanding of MWCNT's foam-stabilizing mechanism, restricting its application as the foam stabilizer. Herein, this paper aims to systematically study the foamstabilizing performance and mechanism of different surfactant/MWCNT foam systems. Combining with the experimental results obtained from ultraviolet and visible spectrophotometry and zeta potential tests, environmental scanning electron microscope analyses, contact angle measurements, optical microscope observations, and surface tension and dilational viscoelastic modulus determinations, the foam-stabilizing mechanism of different surfactant/MWCNT foam systems can be conjectured as follows. Compared with anionic and nonionic surfactants (SDS and OP-10) modified MWCNT, the MWCNT modified by the cationic surfactant (CTAB) can yield better dispersity due to the larger electrostatic repulsion and higher steric resistance between MWCNTs after the adsorption of CTAB. The highly dispersed MWCNTs have small sizes, which make them enter the foam film easily and tend to aggregate at Plateau border. These aggregations can significantly slow down the film drainage. In addition, MWCNTs can improve the viscosity of foam film, which helps to increase the resistance of gas diffusion and mitigate bubble coalescence. After being adsorbed by surfactants, the modified MWCNT can adsorb on the air-water interface. Due to the higher detachment energy, the CTAB modified MWCNT has a stronger adsorption capacity at the air-water interface compared with SDS and OP-10 modified ones. This tight adsorption can improve the dilational viscoelastic modulus and thus enhance foam stability. Finally, the dualsand pack experiments proved that the CTAB/MWCNT stabilized foams have good potential for conformance control in heterogenous reservoirs.

Automated summary

This paper systematically studies the foam-stabilizing performance and mechanism of different surfactant/MWCNT foam systems. The results show that MWCNT modified by the cationic surfactant CTAB exhibits better foam stability, slows down film drainage, increases foam viscosity, and enhances foam stability. As a result, CTAB/MWCNT stabilized foams have potential for conformance control in heterogeneous reservoirs.