MEAM Ph.D. Thesis Defense: “Surface and Interface Engineering in Manipulation and Fabrication of Colloid-Based Sub-Microporous Hierarchical Materials and Their Applications”

Nanolattices exhibit attractive mechanical, energy conversion, and optical properties, but it is challenging to fabricate nanolattices in large scale while maintaining the dense hierarchical nanometer features that enable their properties. Current advanced fabrication methods, like 3D printing or self-assembly, are significantly limited by their scalability or the cracking problem in the assembled templates. This work focuses on self-assembly of metallic inverse opals, a particular type of nanolattices, to overcome these limitations via developing a theoretical model for understanding the cracking problem and a crack-free self-assembly method to scale-up the fabrication and to characterize and explore applications of metallic inverse opals.

The developed model incorporates film yielding, particle order, and interfacial friction to explain several experimental observations and helps solving the cracking problem. It is found that the key to solving the cracking problem is to manipulate the surface and interface properties of particles and substrates. The developed crack-free self-assembly approach results in centimeter-scale nickel inverse opals with much larger crack-free area than prior self-assembled and much more unit cells than 3D-printed nanolattices, demonstrating a tensile strength of 260 MPa. It is also found that drop-casting can achieve fast, high-quality, and large-scale self-assembly via pre-assembly in highly concentrated micro/nanoparticle suspension.

Based on these development and findings, two applications of metallic inverse opals have been demonstrated, including a mechanochromic bending sensor and a magnetic sorting chip for capturing disease-related extracellular vesicles. The developed sensor is wireless and power-free, can utilize full visible spectrum, and has a 10X higher strain sensitivity than other mechanochromic sensors. The fabricated sorting chip achieves >109 nanoscale magnetophoretic sorting devices in a postage-stamp-sized lattice with >70x magnetic traps and >20x improved enrichment for magnetic nanoparticles versus previous studies.

The understanding of cracking in particle templates, the developed self-assembly methods, and the application demonstrations reported in this work may advance the fabrication and applications of high-strength multifunctional porous materials, providing fundamental insights into the design, synthesis, and control of complex hierarchical materials that employ colloid self-assembly.