Voxelated Molecular Patterning in Three-Dimensional Freeforms

Abstract

The ability to pattern material response, voxel by voxel, to direct actuation and manipulation in macroscopic structures can enable devices that utilize ambient stimuli to produce functional responses at length scales ranging from the micro- to the macroscopic. Fabricating liquid crystalline polymers (LCPs), where the molecular director is indexably defined in three-dimensional (3D) freeforms, can be a key enabler. Here, the combination of anisotropic magnetic susceptibility of the liquid crystalline monomers in a reorientable magnetic field and spatially selective photopolymerization using a digital micromirror device to independently define molecular orientation in light and/or heat-responsive multimaterial elements, which are additively incorporated into 3D freeforms, is exploited. This is shown to enable structural complexity across length scales in nontrivial geometries, including re-entrant shapes, which are responsive to either heat or light. A range of monomer compositions are optimized to include photoinitiators, light absorbers, and polymerization inhibitors to modulate the polymerization characteristics while simultaneously retaining the tailorability of the nematic alignment. The versatility of this framework is illustrated in an array of examples, including (i) thermomechanical generation of Gaussian-curved structures from flat geometries, (ii) light-responsive freeform topographies, and (iii) multiresponsive manipulators, which can be powered along independent axes using heat and/or light. The ability to integrate responses to multiple stimuli, where the principal directions of the mechanical output are arbitrarily tailored in a 3D freeform, enables new design spaces in soft robotics, micromechanical/fluidic systems, and optomechanical systems.

Keywords: 4D printing; additive manufacturing; liquid crystal polymers; smart materials; soft robotics.