Tailoring re-entrant geometry in inverse colloidal monolayers to control surface wettability
Tailoring re-entrant geometry in inverse colloidal monolayers to control surface wettability
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DOI：
10.1039/c5ta08992a
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发表时间：
2016-05
影响因子：
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通讯作者：
Stefanie Utech;K. Bley;J. Aizenberg;N. Vogel
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文献类型：
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作者：
Stefanie Utech;K. Bley;J. Aizenberg;N. Vogel
控制与结构化表面接触的液体的微观润湿状态是通过防止或使得给定液体能够渗透表面结构来设计液体排斥性以及防雾涂层的基础。类似地，通过局部控制润湿状态，液体可以被限制在指定的表面区域，应用范围从表面上的液体运输到为细胞培养或化学合成创建定制的微环境。与水相比，控制低表面张力液体的润湿要困难得多，并且需要具有悬垂特征的表面结构，称为凹进几何形状。在这里，我们使用胶体自组装和模板来创建具有定制的凹进几何形状的二维纳米孔阵列。这些孔阵列，被称为反单层，制备牺牲胶体单层与硅溶胶-凝胶前体材料。改变前体浓度使我们能够控制胶体嵌入二氧化硅基质的程度。在煅烧时，产生具有不同开度角的纳米孔。孔开度角与表面纳米结构的凹入曲率直接相关，并且可用于控制位于表面结构上的液体的宏观润湿行为。我们表征的润湿的各种液体的静态和动态接触角，并找到相关的实验结果和理论预测的润湿状态的基础上简单的几何考虑。我们证明了创造的全憎性表面涂层，支持Cassie-Baxter润湿状态的液体具有低表面张力，包括辛烷（γ = 21.7 mN m−1）。我们进一步使用光刻法以高精度在空间上将这种低表面张力液体限制在衬底的期望区域。
Controlling the microscopic wetting state of a liquid in contact with a structured surface is the basis for the design of liquid repellent as well as anti-fogging coatings by preventing or enabling a given liquid to infiltrate the surface structures. Similarly, a liquid can be confined to designated surface areas by locally controlling the wetting state, with applications ranging from liquid transport on a surface to creating tailored microenvironments for cell culture or chemical synthesis. The control of the wetting of a low-surface-tension liquid is substantially more difficult compared to water and requires surface structures with overhanging features, known as re-entrant geometries. Here, we use colloidal self-assembly and templating to create two-dimensional nanopore arrays with tailored re-entrant geometry. These pore arrays, termed inverse monolayers, are prepared by backfilling a sacrificial colloidal monolayer with a silica sol–gel precursor material. Varying the precursor concentration enables us to control the degree to which the colloids are embedded into the silica matrix. Upon calcination, nanopores with different opening angles result. The pore opening angle directly correlates with the re-entrant curvature of the surface nanostructures and can be used to control the macroscopic wetting behavior of a liquid sitting on the surface structures. We characterize the wetting of various liquids by static and dynamic contact angles and find correlation between the experimental results and theoretical predictions of the wetting state based on simple geometric considerations. We demonstrate the creation of omniphobic surface coatings that support Cassie–Baxter wetting states for liquids with low surface tensions, including octane (γ = 21.7 mN m−1). We further use photolithography to spatially confine such low-surface-tension liquids to desired areas of the substrate with high accuracy.