Monolayer Studies of Polyethylene Oxide Octadecanols

The Force-Area (F-A) isotherms of the Polyethylene oxide octadecanol (PEO) monolayers at the air-water interface have been studied. The number of ethylencoxide units and temperature have been varied. Various salt solutions are used as subphase. The expansion of F-A isotherms of PEO monolayers appear to be due to the increasing intermolecular interaction between the underlying water molecules and the hydrophilic part of the film molecules, when the number of EO units increases. The elevation of temperature breaks the associated structure of water hence stronger interaction between film molecules and water overcomes the cohesive forces of aliphatic chains causing the expansion of PEO monolayers. The influence of anions like sulphate, chloride, nitrate and prechlorate etc., on the water structure and hence on the monolayers are discussed. Free energy of compression or "energy of dehydration" has been calculated and discussed with the "structure-temperature" (T str.) of various salts. The increasing concentration of NaClO₄ affects these monolayers in a similar way as by temperature increases.