Stabilization of foams solely with polyoxyethylene-type nonionic surfactant

Abstract Long-term stability is desirable for many foam-based systems, but achieving it is rather difficult. We report how foams can be stabilized solely with nonionic surfactant of the polyoxyethylene dodecyl ether (C 12 EO n ). Effects of concentration and EO chain length of surfactants namely C 12 EO 3 , C 12 EO 5 , C 12 EO 7 and C 12 EO 9 on foaming properties (foamability and foam stability) were considered. The liquid drainage profiles of foams prepared were determined by reading the volume of the liquid drained as a function of time. The microstructure and viscosities on these colloidal systems were studied using optical microscopy and viscosimeter in attempt to explore the stability mechanisms. The experimental results suggest that the foamability goes through a maximum at the concentration of 10 wt.%, respectively, except for C 12 EO 7 . The optimal concentration of C 12 EO 7 displaying maximum foaming capacity is at 1 wt.%. The stability of foams increases with increment of surfactant concentration. Foams stabilized solely by C 12 EO 3 and C 12 EO 5 at the concentration of 30 wt.%, respectively, exhibit the presence of lamellar liquid crystal adsorbed at the air/liquid interface, and could maintain more than 20 h without occurrence of collapse. In the case of foams generated from C 12 EO 7 and C 12 EO 9 under same concentration, respectively, there is no any optical fine structure between two air bubbles and thus has a poor stability only for tens of minutes. It is concluded that the stability of foams stabilized solely by C 12 EO n surface active agents is attributed to the presence of lamellar liquid crystalline phases located at the gas/liquid interface. The role of liquid crystal in stabilizing foams could be explained in several mechanisms including hydrodynamic drainage, the mechanical strength of the liquid film and the diffusion rate of entrapped gas. The drainage behavior from these foams was well fitted by the empirical equation V t  =  V max t n /( K n  +  t n ) and the mechanism of liquid drainage was also discussed.