Wetting of Auxetic Metamaterials

人们普遍认为，当材料被拉伸时，它会变得更薄。然而，当拉胀材料被拉伸时，它变得更宽（它具有负泊松比）。因为材料从来都不是无限的，所以它们都有表面。表面不可避免地与液体接触。然而，令人惊讶的是，没有发表的研究考虑拉胀材料的不寻常性质如何改变固液相互作用，并影响液体如何在固体表面上扩散或液滴的冲击和反弹行为。更令人惊讶的是，膨胀型聚四氟乙烯（ePTFE），GoreTex中的微孔超疏水防水透气层，可以很容易地转化为拉胀形式。 当拉胀材料扩大其表面积时，它是通过增加晶格的固体框架内的空间来实现的。因此，我们可以预期表面润湿特性的变化。这种类型的变化将导致表面的固体表面（Cassie）分数随着固体组分之间的空间增加而减少。固体和液体表面积之间的这种平衡对于表面化学性质如何通过表面形貌/纹理放大成超液体排斥性、半芯吸性和其他润湿性质是至关重要的。它还控制表面是液体会粘在上面还是液体看起来很滑。拉胀材料具有不寻常的抗冲击性能，因为材料朝向而不是远离冲击区域流动。这为液滴冲击和反弹提供了一种新的材料和表面方法。因此，在这个项目中，我们专注于使材料科学创造一种新的润湿材料，我们称之为“非磁性润湿超材料”。该项目考虑了一系列制造拉胀材料的技术，重点关注固体表面积分数和空间面积分数之间的平衡如何随着应变而变化。该项目考虑了这种固体表面积分数如何随应变变化，结合亲水性和疏水性，以操纵表面的整体润湿性和这些新材料的润湿状态转变。它将通过实验进行，并得到理论方案以及建模和模拟的支持。这项工作还将考虑如何应变可以用来控制液体摩擦和液滴反弹。

It is a common conception that when a material is stretched it becomes thinner. However, when an auxetic material is stretched it becomes wider (it possesses a negative Poisson's ratio). Since materials are never unbounded, they have surfaces. And surfaces inevitably come into contact with liquids. However, surprisingly, there is no published research that considers how the unusual properties of auxetic materials change the solid-liquid interaction and influence how liquids spread on the solid surface or the impact and rebound behaviour of droplets. It is even more surprising because expanded polytetrafluoroethylene (ePTFE), the microporous superhydrophobic waterproof and breathable layer in GoreTex, can be easily converted to an auxetic form. When auxetic materials expand their surface area, it is by an increase in the space within the solid frame of a lattice. We can therefore expect changes to the wetting properties of the surface. This type of change will cause the solid surface (Cassie) fraction of the surface to decrease as the space between solid components increases. This balance between solid and liquid surface area is critical to how the surface chemistry properties are amplified by the surface topography/texture into super-liquid repellence, hemi-wicking and other wetting properties. It also controls whether the surface is one to which a liquid will stick or one which appears slippery to a liquid. An auxetic material has unusual impact resistance properties because material flows towards, rather than away, from the area of an impact. This offers a new approach to materials and surfaces for droplet impact and rebound.In this project we therefore focus on the enabling materials-science to create a new class of wetting materials, which we refer to as "Auxetic Wetting Metamaterials". The project considers a range of techniques to fabricate auxetic materials with a focus on how the balance between solid surface area fraction and space area fraction change with strain. The project considers how this solid surface area fraction change with strain combines with hydrophilic and hydrophobic properties to manipulate the overall wetting properties of the surfaces and the wetting state transitions of these new materials. It will do so experimentally and be supported by a theoretical programme and by modelling and simulation. The work will also consider how strain can be used to control liquid friction and droplet rebound.