Nanomanufacturing of Surfaces for Energy Efficient Icing Suppression

不受欢迎的结冰会造成很多破坏——从削弱家用冰箱的能源效率到由于基础设施部件和飞机上的积冰而导致的破坏性事故。这项提议的研究旨在解决这个普遍存在的问题，使用精确的，但潜在的可扩展的技术来纳米工程的憎冰表面，可以抑制冰的形成，抵抗冷滴的冲击，并且与冰的粘附最小。该提案的动机是提供一种可行的、被动的和节能的替代方案，以替代目前使用的防冰技术，这些技术要么依赖于影响系统效率和运行成本的电热系统，要么使用对环境不利的化学物质。所采用的表面纳米工程将包括对纳米级表面纹理和表面疏水性的精确控制。这两个方面的适当结合不仅可以抑制严重过冷条件下（零度以下）的冰形成，还可以抵抗高速过冷液滴的冲击，并最大限度地减少冰在表面的粘附——所有这些方面都与实际应用中的结冰有关，将在当前的工作中进行测试。该提案的目标是制造具有纳米孔阵列的纳米纹理表面，其精度优于10纳米（即分辨率）。根据PI先前引入的热力学非均相冰核框架，并得到文献中原子模拟结果的支持，这种精确和圆形的形貌有望抑制冰的形成。此外，疏水分子在表面的自组装将允许控制表面能，这与纹理控制相结合，将有助于产生超疏水表面，可以抵抗高速，冷滴的刺穿，并且具有低冰粘附性。在冻雨条件下，抗水滴刺穿可以帮助避免飞机和室外基础设施结冰。作为一种潜在的可扩展的、精确的纳米纹理的概念验证，当前的项目将利用嵌段共聚物（BCP）制备的聚合物纳米孔薄膜作为模板，利用金属的电化学阳极氧化。表面纹理将被限制在衬底的顶部~100纳米或更低的厚度，并且只使用温和的阳极氧化条件。模板阳极氧化非常适用于航空航天、制冷和汽车工业中普遍使用的铝和钛基板；然而，类似的模板蚀刻方法可以开发用于其他应用的基板（参见影响的途径部分）。PI先前的工作表明，导热基板可以更好地阻止表面上的冷滴形成霜，因此金属基板是一个非常好的选择。此外，本研究首次引入了一种新的方法，即使用简单的阳极表面投影将BCP纳米孔模板本身的分辨率提高到~ 10nm的精度，通过这些精确模板阳极氧化的表面有望成为理想的疏冰性材料。所得到的阳极氧化底物将通过与疏水性分子功能化而呈现疏水性。这些精确纳米结构的疏水表面不仅具有圆形的纳米级形貌，而且具有最小的固液接触面积，从而进一步抑制结冰的可能性。合成的表面将接受三组测试：它们抵抗高速、过冷落点的穿透能力（目标：25米/秒）；在不同湿度水平的过冷条件下延迟结冰的能力（目标：在-25摄氏度下2小时）；并尽量减少它们与冰冻（冰）滴的粘附。

Undesirable ice formation causes a lot of disruption - from impairing energy efficiency of household refrigerators to causing destructive accidents due to ice accumulation on infrastructure components and airplanes. The proposed research aims to address this ubiquitous problem using precise, but potentially scalable techniques to nanoengineer icephobic surfaces that can suppress ice formation, resist impact of cold drops and have minimal adhesion to ice. The proposal is motivated to provide a viable, passive and energy efficient alternative to the currently employed anti-icing techniques, which rely either on electro-thermal systems that affect the system efficiency and running costs, or make use of environmentally adverse chemicals. The surface nanoengineering to be employed will involve a precise control of both the surface texture at nanoscale and the surface hydrophobicity. The appropriate combination of these two aspects is expected to not only suppress ice formation in severely supercooled conditions (at sub-zero temperatures), but to resist impact of high speed supercooled droplets and minimize adhesion of ice on the surface - all these aspects are relevant to icing in practical applications and will be tested in the current work.The ambition of the proposal is to make nanotextured surfaces with nanohole arrays with better than 10 nm precision (i.e. resolution). Such precise and rounded morphologies are expected to suppress ice formation according to the thermodynamic heterogeneous ice nucleation framework previously introduced by the PI and supported by atomistic modelling results in the literature. In addition, self-assembly of hydrophobic molecules on the surfaces will allow a control over the surface energy, which, in combination with the texture control, will help produce superhydrophobic surfaces that can resist impalement by high speed, cold drops, and have low ice adhesion. The drop impalement resistance can help avoid icing on aircrafts and outdoor infrastructure elements in freezing rain conditions. As a proof-of-concept for a potentially scalable, precise nanotexturing, current project will exploit electrochemical anodisation of metals through polymeric nanohole films, prepared using block-copolymers (BCP), serving as templates. The surface texturing will be limited to top ~100 nm or lower thickness of the substrate and only mild anodisation conditions will be used. The templated anodisation is well suited to aluminium and titanium - substrates prevalent in aerospace, refrigeration and automotive industry; however, similar templated etching approaches can be developed for substrates in other applications (see the PATHWAYS TO IMPACT section). PI's prior work has shown that thermally conductive substrates are better for arresting frost formation from cold drops lying on the surface, thus the metallic substrates are a very good choice. In addition, the current work, for the first time, introduces a novel means to use simple anodic surface projections to improve the resolution of BCP nanohole templates themselves to ~10 nm precision - surfaces anodised through these precise templates are expected to be ideally suited for icephobicity. The resulting anodised substrates will be rendered hydrophobic by functionalizing with hydrophobic molecules. These precisely nanotextured hydrophobic surface are expected to suppress icing not only due to their rounded nanoscale morphology, but will also feature minimal solid-liquid contact area, thereby further suppressing the icing probability. The synthesized surfaces will be subjected to three set of tests: their ability to resist impalement by high speed, supercooled drops (target: 25 m/s); ability to delay ice formation in supercooled conditions at different humidity levels (target: 2 hours at -25 degrees Centigrade); and minimize their adhesion to frozen (ice) drops.