Department of Mechanical Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, New Jersey 07030, United States.
ACS Appl Mater Interfaces. 2012 Feb;4(2):842-8. doi: 10.1021/am201514n. Epub 2012 Jan 18.
Conventional electrochemical anodizing processes of metals such as aluminum typically produce planar and homogeneous nanopore structures. If hydrophobically treated, such 2D planar and interconnected pore structures typically result in lower contact angle and larger contact angle hysteresis than 3D disconnected pillar structures and, hence, exhibit inferior superhydrophobic efficiency. In this study, we demonstrate for the first time that the anodizing parameters can be engineered to design novel pillar-on-pore (POP) hybrid nanostructures directly in a simple one-step fabrication process so that superior surface superhydrophobicity can also be realized effectively from the electrochemical anodization process. On the basis of the characteristic of forming a self-ordered porous morphology in a hexagonal array, the modulation of anodizing voltage and duration enabled the formulation of the hybrid-type nanostructures having controlled pillar morphology on top of a porous layer in both mild and hard anodization modes. The hybrid nanostructures of the anodized metal oxide layer initially enhanced the surface hydrophilicity significantly (i.e., superhydrophilic). However, after a hydrophobic monolayer coating, such hybrid nanostructures then showed superior superhydrophobic nonwetting properties not attainable by the plain nanoporous surfaces produced by conventional anodization conditions. The well-regulated anodization process suggests that electrochemical anodizing can expand its usefulness and efficacy to render various metallic substrates with great superhydrophilicity or -hydrophobicity by directly realizing pillar-like structures on top of a self-ordered nanoporous array through a simple one-step fabrication procedure.
传统的金属电化学阳极氧化工艺（如铝）通常会产生平面和均匀的纳米孔结构。如果进行疏水处理，这种二维平面且相互连接的孔结构通常会导致比三维不连续的柱状结构更低的接触角和更大的接触角滞后，因此表现出较差的超疏水性效率。在本研究中，我们首次证明可以通过工程化阳极氧化参数来设计新型的柱上孔（POP）混合纳米结构，直接在简单的一步制造工艺中实现，从而有效地从电化学阳极氧化过程中实现优异的表面超疏水性。基于在六边形阵列中形成自有序多孔形态的特征，通过调节阳极氧化电压和时间，可以在温和阳极氧化和硬阳极氧化模式下，在多孔层上形成具有受控柱状形态的混合纳米结构。氧化金属氧化物层的混合纳米结构最初会显著提高表面亲水性（即超亲水性）。然而，在疏水单层涂层后，这种混合纳米结构表现出了优异的超疏水性，而这是传统阳极氧化条件下产生的普通纳米多孔表面无法实现的。这种良好调控的阳极氧化工艺表明，电化学阳极氧化可以通过直接在自有序纳米多孔阵列上实现柱状结构，从而通过简单的一步制造工艺赋予各种金属基底优异的超亲水性或超疏水性，从而扩大其用途和效果。
