Film pressure-area isotherms of monolayers of diethylene and triethylene glycol monooctadecyl ether and of diethylene glycol monodocosyl ether on water

Abstract

The film pressure-area isotherms of monolayers on a water surface for diethylene glycol monooctadecyl ether C₁₈·(OC₂H₄)₂OH, triethylene glycol monooctadecyl ether C₁₈·(OC₂H₄)₈OH, and diethylene glycol monodocosyl ether C₂₂·(OC₂H₄)₂OH in the temperature range 15°-35°C. are reported. The C₁₈-compounds exhibit the expanded type whereas the C₂₂·(OC₂H₄)₂OH exhibits condensed films in this range, and even at high film pressures of 40 dynes/cm. none of these indicated the presence of the solid phase. The area at zero compression for the L₀ state is ·27-28A² for the C₁₈· and C₂₂·(OC₂H₄)₂OH, and ·33A² for C₁₈·(OC₂H₄)₃OH. The results have been compared with those for the long-chain fatty alcohols (C_n-OH) and their monoethylene oxide condensation products C_n-OC₂H₄OH. The lowering of the film expansion temperature with the addition of an ethylene oxide unit is continued in the former two compounds as seen previously for C₁₄· and C₁₆·OC₂H₄OH in this temperature range.