Adsorption of end-functionalized poly(ethylene oxide)s to the poly(ethylene oxide)-air interface

Samples with one or both ends of monodisperse poly(ethylene oxide) (PEG) functionalized with perfluorodecanoyl groups (PEO(F) or PEO(2F)) were synthesized and blends of these end-capped PEOs with PEOs of the same molecular weight (M(n) similar to 2000 to similar to 16000 K) were prepared as cast films. As-cast and annealed samples were analyzed by X-ray photoelectron spectroscopy (XPS) and contact angle analysis. XPS analysis was also performed on samples at elevated temperatures (melts). Due to the lower surface energy of the fluorocarbon end groups, the modified PEOs preferentially adsorb to the free polymer surface. The surface concentration of the perfluoroalkyl end groups was measured by XPS which indicates that perfluoroalkyl chain ends adsorb to the polymer surface in a reasonably close-packed fashion (at all molecular weights) and leave a zone depleted of fluorine immediately beneath the highly fluorinated surface region. The dependence of adsorption on temperature was investigated for one sample and adsorption appears to be: slightly favored at lower temperatures. pEO(2F) samples are found to have a slightly higher surface affinity than PEO(F) of the same molecular weight. There is only a slight effect of molecular weight on surface fluorine content, indicating a ''stretched brush'' conformation for the higher molecular weight samples.