Tailoring Material and Mechanochemical Responses with Microstructure

Abstract

The objectives of this project were twofold: (i) to develop a methodology for tailoring the nonlinear elastic response of a 2D lattice material through designed microstructural geometric nonlinearities; and (ii) to show that activation of mechanophores (such as spiropyran) can be similarly manipulated through lattice geometry. Exploring this space may lead to new materials that can be engineered to yield prescribed mechanical and chemical loading responses, such as dissipating or focusing energy when struck or triggering chemical reactions under certain loads. The ability to customize these properties in a systematic way could facilitate the design and fabrication of advanced energetic, impact-mitigating, self-healing or self-reinforcing materials. In this thesis, a heuristic exploration of 2D nonlinear lattices was conducted, in which lattices were designed, modeled in COMSOL, and then 3D printed and quasi-statically tested to validate simulation results. A lattice that softens under compression, as well as two that stiffen under compression (using contact and non-contact based mechanisms) were created. A nonlinear topology optimization scheme using a MATLAB genetic algorithm and COMSOL Finite Element Analysis (FEA) was also created to find structures to match prescribed force-displacement curves: however, this topology optimizer struggled finding non-unique solutions and poorly connected structures. Spiropyran was embedded in PDMS and studied in quasi-static and dynamic compression. It was found that spiropyran activated at compressive strains greater than 0.7 at both high and low strain rates and in less than 8 ms during dynamic tests. Finally, spiropyran was embedded in PCL and printed into an oval pore lattice shape; these samples, as well as control (non-lattice, bulk) samples were subjected to tensile tests. As spiropyran activation in the lattices was observed prior to activation in the control samples, these experiments suggest that microstructure can amplify mechanochemical response.