Solubility Of Monolayers Of Non-Ionic Surfactants At Air-Water Interface

Generally, surfactants can form monolayers at air-water interface, but many of them are unstable because of dissolving, especially when the hydrophicity of the molecules forming the monolayer is strong.The dissertation presented an investigation as to the dissolving property of monolayers of nonionic surfactants:Tween-8(), Peregal(o-20,o-25)and PEGDSs.The influence of oscilating on dissolving of the molecules in a monolayer was strong and it could induce straight decrease of the surface pressure. Without oscilating, spreading solvent梒hloroform evaporated almost absolutely after five to ten minutes, when solution was spreaded onto water surface. Then, surface pressure decreased slowly when time going by and reached a dynamic balance after two or three hours, but reaching thermo-dynamic balance needed a relative long time.The dissolving of material of monolayrs would induce a decrease of the surfacial concentration of the non-ionic surfactants more than half. The surface pressures of monolayers formed by Tween-80, Peregal(o-20), Peregal(o-25), PEGDS-1000 and PEGDS-21XX) decreased when time went by.because material of monolayers could dissolve into water partly, but the surface pressure of PEGDS-300 and PEGDS-6000 were almost unvariable. It was not to say that the monolayers formed by both of them were insoluabk.Thc reason that the surface pressure of PEGDS-6000 was stable was that the hydrophicity of it was strong and the molecules in monotayer reached dissolving balance quickly.Studies on surface pressure-time relationship showed that the influence of the length of PEO was strong on monolayers formed by PEGDSs梩he stronger PEO chain was, the larger surface pressure was, but PEGDS-6000 showed opposite regularity because its hydrophicity was too strong.When surfacial concentration was larger, molecules in monolayers arranged orientedly and the influnce of the length of molecular chain on surface pressure was deduced. Studies on surfacial concentration-time relationship showed that the the longer the PEO chain was, the better the dissolving property was,and the larger the spreading coefficient was.Aslo spreading coefficients decreaded when increaseing the surfacial concentration.But they were not different largely and located on the same number order.