Effect of alkyl tail length of quaternary ammonium gemini surfactants on foaming properties

This paper reports the investigation about the effect of the alkyl tail length of quaternary gemini surfactants, 2-hydroxyl-propanediyl-alpha,omega-bis(dimethylalkylammonium bromide), referred to as m-3(OH)-m, where m represents the number of carbon atoms at each alkyl tail, on the foamability and foam stability. To understand the foaming behavior, the adsorption of surfactants at the air/water interface as well as the dilational viscoelasticity of their films was studied using surface tension and dilational interfacial rheology measurements. 14-3(OH)-14 was found to have stronger foamability and stabilize more efficiently the foam than 12-3(OH)-12, however, 16-3(OH)-16 failed to generate foam. The latter was attributed to the self-coiling of the long hexadecyl tails prior to the adsorption of surfactant at the air/water interface, resulting in the ageing effect of the adsorption behavior. For both 12-3(OH)-12 and 14-3(OH)-14, the results revealed a good correlation between the high limit interfacial elasticity and high stability of foam at the level of identical surface excesses. (C) 2011 Elsevier B.V. All rights reserved.