Stimuli Responsive Polymers in Direct-Ink-Write Additive Manufacturing

Thesis (Ph.D.)--University of Washington, 2020Additive manufacturing (AM) has revolutionized the world of manufacturing. The potential of thetechnology to construct any arbitrary architecture, reduce material cost and the need for an inventory is being widely explored by industry and academia alike. However, AM is currently restricted to processing polymers of “yester-years” which were developed to be amenable to a different set of manufacturing practices. While there has been a dramatic improvement in the hardware aspect of AM, material development still lags behind, limiting the possibilities of the technology. There has been a great effort by scientists to bring forward new materials for additive manufacturing and enable the technology to have a broad scope. One such example is stimuli- responsive polymers which respond to environmental cues. This thesis explores the development of new stimuli responsive materials for direct-ink write additive manufacturing, based on Pluronic F127, a commercially available triblock copolymer consisting of poly(ethylene oxide) and poly(propylene oxide). In the body of work reported here, the polymer has been used in combination with aqueous and ionic liquid solvents to form hydrogels and iongels which are used in direct-ink write 3D printing. The gels are shear responsive themselves and capable of undergoing photo-induced crosslinking to form a polymer network. The rheological requirements of inks for DIW 3D printing is studied in details and several parameters are identified to screen the 3D printability inks .The development of a new 3D printing technique called gel-in-gel printing is reported which facilitates using light sensitive and mechanically weak hydrogels for fabrication of complex architecture. To add functionality to 3D printable inks, the iongel inks are then combined with a spiropyran mechanophores to enable the development of force responsive inks which exhibit an optical signal when stressed. The viscoelastic properties of the gels and the mechanical properties of the final crosslinked network are investigated and conditions necessary for mechanochemical activation of embedded mechanophores are identified. In particular, a suite of inks with highly tunable final material properties were identified which could be used to enable multi-material 3D printing of dual shape morphing objects