Rabani Ramin, Machrafi Hatim, Dauby Pierre
University of Liège, Thermodynamics of Irreversible Phenomena, Allée du 6-Août, 19, BE-4000, Liège, Belgium.
Eur Phys J E Soft Matter. 2017 Oct 17;40(10):89. doi: 10.1140/epje/i2017-11579-3.
In this paper, we study the influence of the upper gas layer on the drying and gelation of a polymer solution. The gel is formed due to the evaporation of the binary solution into (inert) air. A one-dimensional model is proposed, where the evaporation flux is more realistically described than in previous studies. The approach is based on general thermodynamic principles. A composition-dependent diffusion coefficient is used in the liquid phase and the local equilibrium hypothesis is introduced at the interface to describe the evaporation process. The results show that the high thickness of the gas layer reduces evaporation, thus leading to longer drying times. Our model is also compared with more phenomenological descriptions of evaporation, for which the mass flux through the interface is described by the introduction of a Peclet number. A global agreement is found for appropriate values of the Peclet numbers and our model can thus be considered as a tool allowing to link the value of the empirical Peclet number to the physics of the gas phase. Finally, in contrast with other models, our approach emphasizes the possibility of very fast gelation at the interface, which could prevent all Marangoni convection during the drying process.
在本文中，我们研究了上层气体层对聚合物溶液干燥和凝胶化的影响。凝胶是由于二元溶液蒸发到（惰性）空气中而形成的。我们提出了一个一维模型，其中蒸发通量的描述比以往的研究更为实际。该方法基于一般热力学原理。在液相中使用了与组成相关的扩散系数，并在界面处引入了局部平衡假设来描述蒸发过程。结果表明，气体层的厚度较大时会降低蒸发速率，从而导致干燥时间延长。我们的模型还与更具现象学特征的蒸发描述进行了比较，后者通过引入佩克莱数来描述通过界面的质量通量。对于适当的佩克莱数取值，我们发现了整体的一致性，因此我们的模型可被视为一种工具，能够将经验性佩克莱数的值与气相物理联系起来。最后，与其他模型不同的是，我们的方法强调了在界面处非常快速凝胶化的可能性，这可能会在干燥过程中阻止所有的马兰戈尼对流。
