For large ether molecule surfactants with an alkane tail as the hydrophobic moiety and an ethylene oxide head (C2H4O) (POE) as the hydrophilic moiety, water surface tension drop in their presence is triggered by the attraction of water molecules to hydrophilic POE heads of surfactants at the air-water interface, which can be related to interactions between POE chains. It was found that interactions between POE chains decayed exponentially with respect to separation distance and increased with increase in POE chain length. (C) 2003 Elsevier B.V. All rights reserved.