Reducing droplet contact time for green and breathable water repellent rainwear

织物的透气性通常需要大孔隙以允许水分蒸发，而防水性则需要尽可能小的孔隙（或没有）。这个项目的目标是通过最小化水滴和织物之间的接触时间来开发透气和防水的雨衣。随着时间的推移，水滴会渗入纺织品的毛孔，如果这段时间很短，就可以实现能呼吸和排斥雨滴的织物。将研究两种流体动力学技术，以最大限度地减少液滴在织物上撞击时的接触时间：“煎饼弹跳”和“蝴蝶翼液滴分裂”。这两个概念都将液滴与表面之间的接触时间减少到自然设定的基本限制以下。在煎饼弹跳过程中，液滴与表面的相互作用与普通撞击场景不同。在蝴蝶翅膀的液滴分裂过程中，单个液滴分裂成两个或多个子液滴，这改变了接触的时间。为了观察这两种现象，需要对纺织品表面的结构和化学进行精确的工程处理。一名博士生和一名PDF将利用无害的表面化学物质来功能化纺织品，以实现实现这两种液滴弹跳现象所需的表面特性。PDF将侧重于化学发展，同时博士生将研究表面结构。一旦织物设计正确，两个HQP都将研究撞击液滴的流体动力学。对于宏观纹理，我们将与我们的行业合作伙伴Lululemon Athletica合作，制造新颖的织物结构，然后HQP将对其进行修改。人体角度和运动的模拟效果也将被研究，以确定织物如何在更真实的表面上工作。在项目结束时，我们设想的设计标准是为了实现透气、防水的雨衣。

Fabric breathability typically requires large pores to allow moisture evaporation, and liquid repellency requires as small of pores as possible (or none). The goal of this project is to develop breathable and water repellent rainwear by a minimization of the contact time between droplets and fabrics. Droplets soak into the pores of textiles over time and, if this time is minimal, fabrics that can breath and repel rain drops can be realized. Two fluid-dynamic technologies will be investigated to minimize droplet contact time during impact on a fabric: "pancake bouncing" and "butterfly wing droplet splitting". Both concepts reduce the contact time between droplets and surface below the fundamental limit thought to be set by nature. During pancake bouncing, droplets interact with the surface differently than in commonplace impact scenarios. During butterfly wing droplet splitting a single droplet is split into two or more sub-droplets, which alters the time of contact. Precise engineering of the textile's surface's structure and chemistry is required to observe both phenomena.One PhD student and one PDF will utilize non-hazardous surface chemistries to functionalize textiles in order to achieve the surface properties required to enable these two droplet-bouncing phenomena. The PDF will focus on the chemistry development while concurrently the PhD student works on the surface structure. Both HQP will investigate the hydrodynamics of impacting droplets once the fabrics are correctly designed. For macroscopic texturing we will work with our industry partner Lululemon Athletica to fabricate novel fabric structures that HQP will then modify.The simulated effect of body angle and movement will also be investigated, in order to determine how the fabrics work on more realistic surfaces. By the end of the project we envisage design criteria to be constructed in order to realize breathable, water-repellent rainwear.