Crystallization of Poly(ethylene oxide) on the Surface of Aqueous Salt Solutions Studied by Grazing Incidence Wide-Angle X-ray Scattering.

We report the thin layer crystallization of high-molar mass poly(ethylene oxide) (PEO) on a liquid support using a 4 M K2CO3 aqueous solution as a subphase. Because of the Hofmeister effect, PEO does not dissolve and remains at the surface during compression on a Langmuir trough. The transition from the flat pancake conformation upon compression of the spread polymer film to an entangled monolayer results in a plateau region of the Langmuir isotherm. Using grazing incidence wide-angle X-ray scattering, the final crystallization of PEO was observed, and the crystal orientation was determined. The fold surface was (209̅), that is, the helix axis has a tilt angle of 2.9° to the normal vector of the water surface.