Ions at the air/water interface

In a recent review of this topic [B.C. Garett, Science 303 (2004) 1146] the emphasis was on some recent experiments, in which it was found that some anions accumulate at the air/water interface and not in the bulk, as usually happens to the cations, and on some simulations which explained those positive surface adsorption excesses. Because a large number of these experiments could be explained on the basis of some simple physical models proposed by the authors for the interaction between the ions and the air/water interface [M. Manciu, E. Ruckenstein, Adv. Colloid Interface Sci. 105 (2003) 63; Adv. Colloid Interface Sci. 112 (2004) 109; Langmuir 21 (2005) 11312], those models are reviewed in the present note, the goal being to draw attention to them.

Humic acid acts a polyvalent anion neutralizing the positive charges on CTAB micelles in a manner similar to the reaction between charged polymers and surfactants. At high CTAB concentration the hexagonal array structure of CTAB micelles was preserved, though deformed by the interaction, suggesting that there is no regular repetition of structural units in humic acid because such structural regularity would have caused the formation of new CTAB structures.Figure optionsDownload as PowerPoint slide