ORGANIZATION OF POLY(ETHYLENE OXIDE) MONOLAYERS AT THE AIR-WATER-INTERFACE

Poly(ethylene oxide) has been spread at the air-water interface and the organization of the layer investigated using surface pressure isotherms and neutron reflectometry. Surface pressure data lead to the conclusion that the spread polymer is in a thermodynamically favorable environment on pure water which becomes worse as magnesium sulfate is added to the aqueous subphase. However, theta conditions have not been realized over the range of magnesium sulfate molarities used (0.4-0.8 M). Neutron reflectometry data have been analyzed using both optical matrix and kinematic approximation methods. These suggest that, at low surface concentrations (less-than-or-equal-to 0.4 mg m-2), the polymer can be described as a single layer which is much diluted by water. At higher concentrations (up to 1.0 mg m-2), the polymer penetrates the subphase and the segment distribution normal to the interface is describable by a Gaussian concentration profile. As the deposited surface concentration increases, the polymer penetrates deeper into the subphase and the topmost layer concentration remains approximately constant. The layer thickness of the spread monolayer is considerably thicker than the equilibrium surface excess layer obtained in a solution of poly(ethylene oxide). When magnesium sulfate is present in the subphase, the layer thickness is decreased and the polymer concentration of the topmost layer increases considerably.