Glass Transition Accelerates the Spreading of Polar Solvents on a Soluble Polymer
Résumé
We study the wetting of polymer layers by polar solvents. As previously observed, when a droplet
of solvent spreads, both its contact angle and velocity decrease with time as a result of solvent
transfers from the droplet to the substrate. We show that, when the polymer is initially glassy, the
angle decreases steeply for a given value of the velocity, Ug. We demonstrate that those variations
result from a plasticization, i.e. a glass transition, undergone by the polymer layer during spreading,
owing to the increase of its solvent content. By analyzing previous predictions on the wetting of
rigid and soft viscoelastic substrates, we relate Ug to the viscosity of the polymer gel close to glass
transition. Finally, we derive an analytical prediction for Ug, based on existing predictions for the
water transfer from the droplet to the substrate. Using polar solvents of different natures, we show
that the experimental data compares well to the predicted expression for Ug.
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