Evidence of a sticky boundary layer in nanochannels: a neutron spin echo study of n-hexatriacontane and poly(ethylene oxide) confined in porous silicon

Neutron spin echo spectra of the melts of n-hexatriacontane (C36) and poly(ethylene oxide) (PEO), 2 kg/mol, confined in circular channels with a mean diameter of 10 and 12 nm, respectively, in porous silicon, were recorded at Q values between 0.05 and 0.15 Å−1. The spectra were successfully analyzed in terms of a two-state model where wall-adsorbed molecules are immobile and free molecules have a bulk-like dynamics. For C36, we find an adsorbed bilayer at 364 K and a monolayer at 435 K (in both cases, the long axis of the molecules is oriented parallel to the surface) and no adsorbed layer at 512 K. For PEO, we find an adsorbed monolayer at 413 K. The results support the existence of a sticky boundary layer inferred from capillary filling experiments.

DDC Class

530: Physik

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Evidence of a sticky boundary layer in nanochannels: a neutron spin echo study of n-hexatriacontane and poly(ethylene oxide) confined in porous silicon