Triple Ph.D. Defense
| April 28, 2023 — By Ben Skopic |
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The nano & biomaterials group has had a busy spring so far with three dissertation defenses. Samantha Applin, Ben Skopic, and Avishi Abeywickrama are all doctors of philosophy!
First up was Sam with her dissertation titled, “Investigation of Reversibly Assembling Materials Using Force Spectroscopy”. Sam is part of NASA’s pathways program the enables students to be employed by NASA while simultaneously pursuing advanced degrees. Sam’s work was part of a larger NASA project targeting new in-space manufacturing techniques. This manufacturing technique uses functionalized microspheres that can be chemically “clicked” together and apart to create many necessary objects in space reversibly while recycling all materials.
Sam’s research used the atomic force microscope (AFM) to conduct force spectroscopy experiments between the spheres of different functionalities to determine the strength of the adhesion. She was able to measure the “click” chemistry between her functionalized surfaces. This enables her NASA teammates to better understand this new manufacturing system to advance human’s capabilities for long duration space exploration.
Ben Skopic defended April 21st, the day after Sam. His dissertation was titled, Tape-Based Structural Metamaterials”. With record attendance for an Applied Science dissertation defense, Ben delivered an excellent presentation that sparked a fun public discussion about the work. His work focused on tape-based materials and how they are poised to outperform current fiber-reinforced composite materials.
Tapes are overlooked as structurally robust material because they have been designed to have low adhesive strength. However, the recluse spider and some species of silkworms use tapes to make impressive tape-based metastructures that outperform their cylindrical fiber-based counterparts. This impressive performance comes from tape-to-tape adhesive junctions within the materials. The first part of Ben’s work focused on describing the mechanical and failure behaviors of one of these adhesive junctions. This work was published in Materials Horizons in 2022. He took this understanding of a single tape-to-tape junction and extended it to make his own tape and tape-based metamaterials. He showed that these materials have exceptional tensile properties that have never been exhibited by any fiber-reinforced composite.
The third and final defense this spring was delivered by Avishi. Her dissertation was titled, “Direct Measurements of Interfacial Interactions of 2D Materials”. As the title implies, she determined the interfacial interactions between 2D materials and various polymer. A main contribution of Avishi's work is her creation of functionalized colloidal probes. She was the first to adhere and functionalize silica spheres to the end of a tipless cantilever. This allowed her to directly measure the interfacial forces using force spectroscopy.
Her first project focused on measuring the forces at the water-oil interface. She isolated droplets of heptane in water and conducted force spectroscopy experiments using a graphene-oxide functionalize colloidal probe. At different reduction levels of the graphene-oxide, she was able to tune the hydrophobicity of the probe. This allowed her to determine the physical mechanisms behind the hydrophobic force at the oil-water interface. The second project she presented on involved similar force spectroscopy experiments, except this project measured the force between different polymers and graphene and hexagonal boron nitride. These two materials are commonly used as fillers in nanocomposites. The adhesive interactions determine the efficiency of the filler within the composite. Thus, understanding the adhesive forces between these fillers and various polymers used as the matrix is important. Using these specially produced colloidal probes and force spectroscopy, she quantitatively measured these interfacial forces to better produce high-performance nanocomposites.
