Additive Manufacturing of Mechanoresponsive Polymers

Abstract

Polymer mechanochemistry has been investigated for the mechanism of mechanical force-induced chemical reactivity within polymers. Many efforts have been made to fine tune the mechanoresponsiveness of the polymeric materials both in molecular and macroscopic level to broaden the applications of this kind of stimuli-responsive material in engineering field. Additive manufacturing, as an emerging and versatile technology, is widely utilized to create objects with very complex geometries, which makes the study for the effect of geometries on polymer mechanochemistry possible. This dissertation describes the research on additive manufacturing of mechanophore-containing polymers and characterizing the dependence of mechanochemical reactivities of the functional moieties with geometries. Chapter 1 is an introduction to additive manufacturing, polymer mechanochemistry, and the precedent work on combining these two fields. The study of Chapter 2 represents our work on additive manufacturing of a “flex-activated” mechanophore, oxanorbornadiene, with photocurable resins by using vat photopolymerization printing. The characterization of the released small molecules after activation and the influence of the printed geometry are also depicted. Chapter 3 focuses on printing with polymers containing mechanochromic mechanophore, spiropyran, into complex geometries. The areas with the highest localized strain in those geometries can be detected easily by the color change. Chapter 4 introduces the fabrication and characterization of mechanochromic elastomeric sheets that enable the real-time, on-site, dynamic mapping of strain field distribution on objects with hierarchical patterns. Chapter 5 discusses the experimental and computational study on achieving the early onset activation of the mechanophore at much lower global strains in comparison with materials lacking judicious geometric design by tuning the microstructural geometry of the periodic mechanoreponsive polymeric materials.