Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
ACS Nano. 2012 May 22;6(5):3789-99. doi: 10.1021/nn301112t. Epub 2012 May 1.
Designing multifunctional surfaces that have user-specified interactions with impacting liquids and with incident light is a topic of both fundamental and practical significance. Taking cues from nature, we use tapered conical nanotextures to fabricate the multifunctional surfaces; the slender conical features result in large topographic roughness, while the axial gradient in the effective refractive index minimizes reflection through adiabatic index-matching between air and the substrate. Precise geometric control of the conical shape and slenderness of the features as well as periodicity at the nanoscale are all keys to optimizing the multifunctionality of the textured surface, but at the same time, these demands pose the toughest fabrication challenges. Here we report a systematic approach to concurrent design of optimal structures in the fluidic and optical domains and a fabrication procedure that achieves the desired aspect ratios and periodicities with few defects and large pattern area. Our fabricated nanostructures demonstrate structural superhydrophilicity or, in combination with a suitable chemical coating, robust superhydrophobicity. Enhanced polarization-independent optical transmission exceeding 98% has also been achieved over a broad range of bandwidth and incident angles. These nanotextured surfaces are also robustly antifogging or self-cleaning, offering potential benefits for applications such as photovoltaic solar cells.
设计具有特定相互作用的多功能表面，使其与撞击液体和入射光相互作用，这是一个具有基础和实际意义的课题。受自然启发，我们使用锥形纳米结构来制造多功能表面；锥形特征的细长形状导致了大的形貌粗糙度，而有效折射率的轴向梯度通过在空气和基底之间的绝热折射率匹配最小化了反射。锥形形状和特征的细长度以及纳米级的周期性的精确几何控制都是优化纹理表面多功能性的关键，但同时，这些要求也带来了最具挑战性的制造难题。在这里，我们报告了一种在流态和光学领域同时进行最优结构设计的系统方法，以及一种能够实现所需纵横比和周期性、缺陷少、图案面积大的制造工艺。我们制造的纳米结构表现出结构超亲水性，或者与合适的化学涂层结合，表现出坚固的超疏水性。在宽带宽和入射角范围内，还实现了超过 98%的增强的偏振无关光透射。这些纳米纹理表面还具有很强的抗雾性或自清洁性，为光伏太阳能电池等应用提供了潜在的好处。
