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

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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.