CNRS/UPMC/ESPCI ParisTech-PSL Research University, UMR 7615, Laboratoire SIMM, 10 Rue Vauquelin, 75231 Paris, France.
Nestle Research Center, Route du Jorat 57, 1000 Lausanne 26, Switzerland.
Phys Rev Lett. 2014 May 9;112(18):188302. doi: 10.1103/PhysRevLett.112.188302. Epub 2014 May 6.
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 the 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 compare well to the predicted expression for Ug.
我们研究了聚合物层被极性溶剂润湿的情况。如先前观察到的，当溶剂液滴扩展时，由于溶剂从液滴转移到基底，其接触角和速度随时间降低。我们表明，当聚合物最初是玻璃态时，对于给定的速度 Ug 值，角度急剧下降。我们证明，这些变化是由于聚合物层在扩展过程中发生了增塑作用，即玻璃化转变，这是由于溶剂含量的增加造成的。通过分析以前关于刚性和软弹性基底润湿的预测，我们将 Ug 与接近玻璃化转变的聚合物凝胶的粘度联系起来。最后，我们基于从液滴到基底的水传递的现有预测，推导出 Ug 的解析预测。使用不同性质的极性溶剂，我们表明实验数据与 Ug 的预测表达式很好地吻合。
