  We investigate the effect of short chains on slip of highly entangled
polystyrenes (PS) during thin film dewetting from non-wetting fluorinated
surfaces. Binary and ternary mixtures were prepared from monodisperse PS with
weight average molecular weights $5 < M_\textrm{w} < 490$ kg/mol. Flow dynamics
and rim morphology of dewetting holes were captured using optical and atomic
force microscopy. Slip properties are assessed in the framework of hydrodynamic
models describing the rim height profile of dewetting holes. We show that short
chains with $M_\textrm{w}$ below the polymer critical molecular weight for
entanglements, $M_\textrm{c}$, can play an important role in slip of highly
entangled polymers. Among mixtures of the same $M_\textrm{w}$, those containing
chains with $M<M_\textrm{c}$ exhibit larger slip lengths as the number average
molecular weight, $M_\textrm{n}$, decreases. The slip enhancement effect is
only applicable when chains with $M<M_\textrm{c}$ are mixed with highly
entangled chains such that the content of the long chain component,
$\phi_\textrm{L}$, is dominant ($\phi_\textrm{L}<0.5$). These results suggest
that short chains affect slip of highly entangled polymers on non-wetting
surfaces due to the physical or chemical disparities of end groups, and any
associated dynamical effect their presence may have, as compared to the
backbone units. The enhanced slip in this regard is attributed to the impact of
chain end groups or short chain enrichment on the effective interfacial
friction coefficient. Accordingly, for entangled PS, a higher concentration of
end groups or short chains at the interface results in a lower effective
friction coefficient which consequently enhances the slip length.
