Confinement Effect on the Effective Viscosity of Plasticized
Polymer Films
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Abstract
We have measured the effective viscosity
of polystyrene films with
a small (4 wt %) added amount of dioctyl phthalate (DOP) deposited
on silica. A broad range of molecular weights, <i>M</i><sub>w</sub>, from 13.7 to 2100 kg/mol was investigated. Our result shows
that for the thin films with <i>M</i><sub>w</sub> < ∼100
kg/mol the addition of DOP causes the effective viscosity to decrease
by a factor of ∼4, independent of <i>M</i><sub>w</sub>. But for the higher <i>M</i><sub>w</sub> films, the effective
viscosity of the DOP added films creeps toward that of the neat films
with increasing <i>M</i><sub>w</sub>. A model assuming the
effective viscosity to be dominated by enhanced surface mobility for
the lower <i>M</i><sub>w</sub> films but surface-promoted
interfacial slippage for the higher <i>M</i><sub>w</sub> films is able to account for the experimental observations