MEAM Seminar: “Surface and Interface Engineering in Manipulation and Fabrication of Colloid-Based Sub-Microporous Hierarchical Materials and Their Applications”

Micro- and nano-porous hierarchical materials exhibit extraordinary mechanical, energy conversion, and optical properties, but manufacturing challenges prevent them from being fabricated at cm-length scales or larger while maintaining the dense regular nm features that enhance their properties. Using self-assembled particles as a template to fabricate metallic hierarchical structures is promising to overcome these challenges, but current fabrication approaches are significantly limited by the cracking problem in the assembled templates. This work focuses on understanding cracking mechanisms in particle templates and developing a crack-free self-assembly approach to fabricate cm-scale porous nickel hierarchical structures with sub-micrometer feature sizes and an ultrahigh tensile strength. The key to eliminating cracks in the assembled template is to manipulate the surface and interface properties of particles and substrates. The resulting nickel hierarchical structures have 30 nm grains, 100 nm features, and 260 MPa tensile strengths, which are 3X the strength of all porous metals at the same relative density, approach the theoretical strength limit for porous nickel, and are 10X the strength of prior nanolattices. Besides, a new way of controlling internal pore size of the resulting structures has been demonstrated by taking advantage of liquid bridging between particles. The fundamental insights and fabrication methods developed in this work further enable applications, such as immunomagnetic separation of exosomes and mechanochromic sensing.