Matière et Systèmes Complexes, CNRS UMR 7057, Université Paris Diderot, Sorbonne Paris Cité University, F-75013 Paris, France.
Laboratoire Sciences et Ingénierie de la Matière Molle, Paris Sciences et Lettres Research University, École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, CNRS, F-75231 Paris Cedex 05, France.
Proc Natl Acad Sci U S A. 2018 Feb 20;115(8):1748-1753. doi: 10.1073/pnas.1712562115. Epub 2018 Feb 5.
Gel layers bound to a rigid substrate are used in cell culture to control differentiation and migration and to lower the friction and tailor the wetting of solids. Their thickness, often considered a negligible parameter, affects cell mechanosensing or the shape of sessile droplets. Here, we show that the adjustment of coating thickness provides control over energy dissipation during the spreading of flowing matter on a gel layer. We combine experiments and theory to provide an analytical description of both the statics and the dynamics of the contact line between the gel, the liquid, and the surrounding atmosphere. We extract from this analysis a hitherto-unknown scaling law that predicts the dynamic contact angle between the three phases as a function of the properties of the coating and the velocity of the contact line. Finally, we show that droplets moving on vertical substrates coated with gel layers having linear thickness gradients drift toward regions of higher energy dissipation. Thus, thickness control opens the opportunity to design a priori the path followed by large droplets moving on gel-coated substrates. Our study shows that thickness is another parameter, besides surface energy and substrate mechanics, to tune the dynamics of liquid spreading and wetting on a compliant coating, with potential applications in dew collection and free-surface flow control.
附着在刚性基底上的凝胶层被用于细胞培养，以控制分化和迁移，并降低固体的摩擦和润湿性。它们的厚度通常被认为是一个可以忽略的参数，但却会影响细胞的机械感知或固定液滴的形状。在这里，我们展示了通过调整涂层厚度，可以控制流动物质在凝胶层上扩展时的能量耗散。我们结合实验和理论，提供了凝胶、液体和周围大气之间接触线的静态和动态的分析描述。我们从这个分析中提取出一个以前未知的标度律，该定律预测了三个相之间的动态接触角是如何作为涂层的特性和接触线速度的函数。最后，我们表明，在具有线性厚度梯度的凝胶层上移动的液滴会向能量耗散较高的区域漂移。因此，厚度控制为预先设计在涂有凝胶的基底上移动的大液滴的路径提供了机会。我们的研究表明，厚度是另一个参数，除了表面能和基底力学，可用于调节液体在柔顺涂层上扩展和润湿的动力学，这在露水收集和自由表面流控制方面具有潜在的应用。
