3D Printed Silicones with Shape Memory

Abstract

Direct ink writing enables the layer-by-layer manufacture of ordered, porous structures whose mechanical behavior is driven by architecture and material properties. Here, we incorporate two different gas filled microsphere pore formers to evaluate the effect of shell stiffness and T_g on compressive behavior and compression set in siloxane matrix printed structures. The lower T_g microsphere structures exhibit substantial compression set when heated near and above T_g, with full structural recovery upon reheating without constraint. By contrast, the higher T_g microsphere structures exhibit reduced compression set with no recovery upon reheating. Aside from their role in tuning the mechanical behavior of direct ink write structures, polymer microspheres are good candidates for shape memory elastomers requiring structural complexity, with potential applications toward tandem shape memory polymers.

Figure 1

(a) Microballoon diameter size distribution, optical microscopy images of (b) T_g44 and (c) T_g113 microballoons, (d) schematic illustration of our 3D printing process, optical microscopy images of printed silicones with microballoons showing (e) x-y view, (f) x-z view and (g) high magnification image of (f) showing 25 vol% microballoons in a printed filament.

Figure 2

Effect of microballoons on (a) rotational oscillatory response, (b) continuous flow behavior of the ink, and (c) response to compressive loading of the cast and printed structures.

Figure 3

(a) Labeled schematic depicting the shape memory experiment, (b) optical microscopy images showing cross-sectional views of a printed structure with T_g44 microballoons at different stages of the shape memory experiment, (c) shape memory behavior following thermal soak under compressive strain at 70 °C for 70 hours, and (d) time dependent recovery behavior in the T_g44 microballoon prints near T_g and above T_g.