Reptation Dynamics of a Polymer Melt near an Attractive Solid Interface

Abstract

The tracer diffusion coefficients ${D}^{*}$ of polystyrene (PS) chains near PS melt-solid interfaces have been measured by secondary ion mass spectrometry. The ${D}^{*}$ for poly(2-vinylpyridine) (PVP) and oxide (SiO) covered silicon surfaces were smaller by, respectively, \ensuremath{\sim}3 and \ensuremath{\sim}${10}^{2}$ than for diffusion near the vacuum interface. ${D}^{*}$ scaled with degree of polymerization $N$ as ${N}^{\ensuremath{-}\ensuremath{\propto}}$, with ${\ensuremath{\alpha}}_{\mathrm{PVP}}=1.7(1)$ and ${\ensuremath{\alpha}}_{\mathrm{SiO}}=1.5(1)$. These results are in excellent agreement with reptation theory modified to account for increased friction due to surface-monomer contacts. The monomeric friction coefficients were found to be 98 \ifmmode\pm\else\textpm\fi{} 13 (PVP) and 5750 \ifmmode\pm\else\textpm\fi{} 450 (SiO) times greater than the bulk melt values.