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Optimizing the Grafting Density of Tethered Chains to Alter the Local Glass Transition Temperature of Polystyrene near Silica Substrates: The Advantage of Mushrooms over Brushes
journal contribution
posted on 2018-02-09, 12:19 authored by Xinru Huang, Connie B. RothWe
measured the local glass transition temperature Tg(z) of polystyrene (PS) as a function
of distance z from a silica substrate with end-grafted
chains using fluorescence, where competing effects from the free surface
have been avoided to focus only on the influence of the tethered interface.
The local Tg(z) increase
next to the chain-grafted substrate is found to exhibit a maximum
increase of 49 ± 2 K relative to bulk at an optimum grafting
density that corresponds to the mushroom-to-brush transition regime.
This perturbation to the local Tg(z) dynamics of the matrix is observed to persist out to
a distance z ≈ 100–125 nm for this
optimum grafting density before bulk Tg is recovered, a distance comparable to that previously observed
by Baglay and Roth [J. Chem. Phys. 2017, 146, 203307] for PS next to the higher-Tg polymer polysulfone.