UC Santa Barbara

Natural materials have long inspired the design and fabrication of advanced materials. Characterized by intricate structures featuring hierarchical porosity, spatial heterogeneities, and architectural gradients, these materials offer unique combinations of stiffness, strength, and toughness at low density. Inspired by nature, this thesis explores the development of advanced materials through two distinct avenues.In the initial investigation, the adhesive capabilities of marine mussels are examined on various geometry-controlled surfaces. Through mechanical tests, the adhesion strength of mussel structures is assessed, revealing consistent detachment forces . This suggests their robustness to different substrate geometries. Subsequent scanning electron microscopy (SEM) analysis reveals substrate-dependent damages within microstructures, indicating that mussels are capable of changing damage mechanisms to maintain characteristic pull-off force, suggesting their adaptability to geometric conditions. Building upon the insights gained from natural materials, subsequent work focuses on the development of advanced materials using additive manufacturing (AM) techniques. Specifically, digital light processing (DLP) of photocurable resins combined with thermally expandable microspheres is employed to create polymer composite foams that are lightweight yet stiff. A two-step material processing approach enables precise control over porosity with tunable mechanical properties of the materials. Through mechanical analysis under compression, we elucidate how foaming alters the mechanics of the composite material, including changes in modulus, Poisson’s ratio, energy dissipation, and fatigue performance. In the final chapter, we investigate thermally induced transformations in the properties of the polymer foams. We observe that 3D-printed objects undergo extra-curing upon heating above the expansion temperature of the microspheres, indicating that the materials bear latent transformation capabilities. Through comprehensive thermal analysis and mechanical characterization, we identify exothermic reactions at elevated temperatures, along with shifts in the glass transition temperature. This confirms that the processed material still contains unreacted residual monomers, which can lead to on-demand thermal polymerization. An understanding of thermal polymerization kinetics is established, enabling the further tailoring of mechanical properties of the foams post-cure. This work provides insights into the processing-structure-property relationships of additively manufactured composite foams, offering feasible pathways for the design of materials with practical applications across various engineering fields.