Collaborative Research: Multi-Scale Micromechanical Properties of Hierarchical Coatings and Interfaces Fabricated by Self-Limiting Electrospray Deposition

多孔材料在从过滤和建筑到极端环境（如北极、深海和太空）的应用中无处不在。 制造这些材料的方法通常需要批量处理技术，并且可能难以独立地确定性地调整结构和组成。 这项合作研究采用自限制电喷雾沉积（SLED）来创建多孔微膜的受控库，从而能够快速筛选其特征材料和结构参数，同时促进定制的性能可调性。 机械分析涵盖了从准静态到室温或高温下的弹道冲击的测试条件，允许探测材料对热机械刺激的机械响应。 对于弹道分析，使用激光诱导粒子冲击测试（LIPIT），这是一种使用激光推进微粒来产生受控微弹道冲击的创新方法。 这些实验提供了一个半经验模型，反过来又指导了未来实验的方向，最终导致一个平台，用于设计和优化多孔材料的无数应用，包括探索SLED薄膜作为笨重涂层的低厚度替代品。 该项目团队由SLED制造、纳米力学测试和建模以及微弹道分析方面的专家组成。该奖项允许对关键多孔材料合成的理解和控制达到新的水平，有助于美国的竞争力和繁荣。SLED利用带电静电喷雾的排斥力来产生受控厚度的水平薄膜。 喷涂参数控制最终多孔形态的不同方面。 流速控制多孔结构的特征尺度;固体负载控制孔的填充分数;喷涂温度控制孔的熔合程度;并且材料选择控制材料的组成。 将对有或无颗粒和橡胶增强材料以及沿着交联多孔环氧树脂的模型塑料进行评估。 在LIPIT的应变率测试过程中，陶瓷微球通过激光诱导的快速气体膨胀被加速到至多1,000 m/s，并使用超快频闪显微镜进行跟踪。一个强烈的机械脉冲，从而通过微球的碰撞施加到试样，然后可以分析能量耗散和损伤机制。此外，使用较慢的机械刺激方法，纳米冲击（1-20 mm/s）和纳米压痕（10- 1，000 nm/s），在相同的样品上允许在不同范围内的SLED涂层的变形速率相关特性之间进行比较。 这些研究的每个阶段都得到多尺度计算模拟的支持，以创建预测模型，指导实验过程和未来材料的设计。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Porous materials are ubiquitous in applications ranging from filtration and construction to ones in extreme environments, such as the Arctic, deep sea, and space. The methods of manufacturing these materials often require bulk processing techniques, and it can be difficult to deterministically tune the structure and composition independently. This collaborative research employs self-limiting electrospray deposition (SLED) to create controlled libraries of porous microfilms, enabling rapid screening of their characteristic material and architecture parameters while facilitating customized property tunability. Mechanical analysis covering testing conditions from quasi-static to ballistic impact at room or elevated temperatures are undertaken, allowing probing of the materials’ mechanical response to thermomechanical stimulus. For ballistic analysis, laser-induced particle impact testing (LIPIT), an innovative method of using laser-propelled microparticles to create controlled microballistic impact, is used. These experiments inform a semi-empirical model that in turn guides the direction of future experiments, ultimately leading to a platform to design and optimize porous materials for myriad applications, including exploration of SLED thin films as low-thickness alternatives to bulkier coatings. The project team consists of experts in SLED fabrication, nanomechanical testing and modeling, and microballistic analysis. This award allows for a new level of understanding and control of the synthesis of critical porous materials aiding in US competitiveness and prosperity. SLED utilizes the repulsion of the charged electrostatic spray to create level thin films of controlled thickness. Spray parameters control different aspects of the final porous morphology. The flow rate controls the characteristic scale of the porous structure; the solids loading controls the fill fraction of the pores; the spray temperature controls the degree of fusion of the pores; and the materials selection controls the composition of the material. Evaluation of model plastic with and without particle and rubber reinforcement, along with crosslinked porous epoxies, will be performed. During the strain rate testing in LIPIT, a ceramic microsphere is accelerated to at most 1,000 m/s by laser-induced rapid gas expansion and is tracked using ultrafast stroboscopic microscopy. An intense mechanical impulse is thereby applied to the specimen through the collision of the microsphere and can then be analyzed for energy dissipation and damage mechanisms. Moreover, using slower mechanical stimuli methods, nanoimpact (1-20 mm/s) and nanoindentation (10-1,000 nm/s), on the same specimens allows comparison between the deformation-rate-dependent characteristics of the SLED coatings over the different ranges. Each stage of these studies is supported by multiscale computational simulations to create predictive models to guide both the course of the experiments and the design of future materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.