Dip-coating with prestructured substrates: transfer of simple liquids and Langmuir–Blodgett monolayers
Dip-coating with prestructured substrates: transfer of simple liquids and Langmuir–Blodgett monolayers
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DOI：
10.1088/0953-8984/29/1/014002
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发表时间：
2016-07
期刊：
影响因子：
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通讯作者：
M. Wilczek;Juan Zhu;L. Chi;U. Thiele;S. Gurevich
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作者：
M. Wilczek;Juan Zhu;L. Chi;U. Thiele;S. Gurevich
当从液体浴中取出板时，在浴和基板之间的过渡区域中形成静态弯月面，或者将有限厚度的液体膜（Landau-Levich膜）转移到移动基板上。如果衬底是不均匀的，例如具有由不同润湿性的条带组成的预结构，则弯月面可能变形或显示复杂的动态行为。在这里，我们研究的自由表面的形状和动力学的拖曳弯月面发生条纹预结构有两个方向，平行和垂直的转移方向。薄膜模型，占毛细作用通过拉普拉斯压力和空间变化的润湿性通过Derjaguin（或分离）压力。数值延拓用于获得稳定的自由表面轮廓和相应的分叉图的情况下，具有不同的均匀润湿性的基板。直接数值模拟的情况下，各种条纹预结构。最后部分通过对Langmuir-Blodgett转移实验进行建模，说明了我们的发现对于涉及复杂液体的特定应用的重要性。在那里，将覆盖浴表面的不溶性表面活性剂的单层转移到移动基底上。所得到的图案形成现象可以受到弯液面的流体动力学的关键影响，该流体动力学本身取决于基板上的预结构。特别是，我们展示了如何预结构条纹平行于转移方向导致形成的弯曲条纹的表面活性剂覆盖转移后，并提出了类似的实验结果。
When a plate is withdrawn from a liquid bath, either a static meniscus forms in the transition region between the bath and the substrate or a liquid film of finite thickness (a Landau–Levich film) is transferred onto the moving substrate. If the substrate is inhomogeneous, e.g. has a prestructure consisting of stripes of different wettabilities, the meniscus can be deformed or show a complex dynamic behavior. Here we study the free surface shape and dynamics of a dragged meniscus occurring for striped prestructures with two orientations, parallel and perpendicular to the transfer direction. A thin film model is employed that accounts for capillarity through a Laplace pressure and for the spatially varying wettability through a Derjaguin (or disjoining) pressure. Numerical continuation is used to obtain steady free surface profiles and corresponding bifurcation diagrams in the case of substrates with different homogeneous wettabilities. Direct numerical simulations are employed in the case of the various striped prestructures. The final part illustrates the importance of our findings for particular applications that involve complex liquids by modeling a Langmuir–Blodgett transfer experiment. There, one transfers a monolayer of an insoluble surfactant that covers the surface of the bath onto the moving substrate. The resulting pattern formation phenomena can be crucially influenced by the hydrodynamics of the liquid meniscus that itself depends on the prestructure on the substrate. In particular, we show how prestructure stripes parallel to the transfer direction lead to the formation of bent stripes in the surfactant coverage after transfer and present similar experimental results.