X‐ray reflectivity on perfluoropolyether polymer molecules on amorphous carbon

The mass density profile from thin (∼25 A) layers of polymer molecules adsorbed on amorphous carbon thin films is determined from measurements of the specular reflectivity of x rays. Important information on the conformation of the polymer molecules is obtained from the density profile (average density as a function of position above the surface). The polymer is a perfluoropolyether (PFPE) with piperonyl end groups and has a molecular weight of 2000–3000 Daltons. Three samples are measured: a nonbonded sample with an approximately 25 A layer applied by dipping, a bonded sample with the layer applied by dipping but followed by a process to attach the molecule to the carbon, and a cleaned sample which is the nonbonded sample after the polymer had been removed. The density profile of the nonbonded polymer shows that the density within 10 A of the carbon surface is ∼1.6 gm/cc, which is smaller than the density in the region between 10 and 25 A (∼1.8 gm/cc). This indicates that the less dense piperonyl end gro...

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