The effect of polydispersity on the static and dynamic behavior of dodecyl ethoxylates at the air–water interface

The effect of polydispersity of polyoxyethylene chain has been studied with dodecyl alcohol 7 ethoxylates (C12E7) having different homologue distribution at air–water interface. The CMCs and the cross-sectional areas of head groups of C12E7 decreased linearly with the polydispersity of oxyethylene chain. The headgroup areas, deduced from the Gibbs adsorption equation, became small due to the preferential adsorption of short chain molecules onto the surface, whereas the limiting areas of the π–A isotherm at collapse did not change although the polydispersity of C12E7 increased, because they were averaged over all distributions. The effective chain length of oxyethylene decreased on the surface as the polydispersity of C12E7 increased. Also the polydispersity of oxyethylene chain increased the dynamic surface tension at the fresh surface while it decreased the equilibrium surface tension at the aged surface.