Temperature effect of hydrophobically modified polyethylene oxide at the air–water interface

Surface pressure (π)–area (A) isotherms of hydrophobically modified polyethylene oxide (HEUR) at the air–water interface was examined. Conformational transitions between pancake, mushroom, and brush states of the hydrophilic backbone influence the intermolecular interaction between the hydrophobic chains. We choose relatively long (18 carbons) hydrophobic ends, which have large hydrophobic interactions, and investigate the main chain effect by change in the length of the hydrophilic PEO chain. At high surface concentration region, the temperature coefficient of surface pressure, dπ/dT, was larger by increasing the portion of the hydrophobicity. This indicates an increase in surface energy and a decrease in surface enthalpy at high surface concentrations. As alkyl chains on both sides of HEURs are anchored at the air–water interface, restriction caused by the alkyl chain would be smaller for the long PEO chain, but the larger for the short PEO chain length.