3D printing of molecularly ordered freeforms

In liquid crystal elastomers (LCE), functionality arises from anisotropy. The orientational order of rod-shaped mesogens defines their non-linear strain response to applied deformation, characterizes the birefringence and directs their actuation in response to stimuli. These attributes enable systems that tune dissipation and adhesion via soft elasticity, unlock hierarchically architected optical systems, and power soft robots with their photo-, thermo-, and electro-mechanical actuation. Where, molecular order defines the properties, spatially patterning the molecular orientation in microstructural domains becomes a design tool.



3D liquid crystalline freeforms where the molecular order can be voxelated at will is a rich design space. Additive manufacturing with LCE to accomplish this fall under two classes: i) magnetically assisted stereolithography (SLA) using liquid crystalline monomer mixtures and ii) Direct-ink-writing (DIW) using mesogenic oligomers. SLA-based methods that use the combination of magnetically assisted alignment and spatially selective polymerization offer a pathway for highly refined patterning of molecular order. Furthermore, encoding the molecular order using an orthogonal stimulus (magnetic field) that is decoupled from the material accretion (photopolymerization) allows independent indexing of the responsiveness, voxel-by-voxel. In contrast, DIW-based printing has been used to fabricate LCE freeforms, where molecular order is enforced via shear during the material deposition. This approach has allowed for the scalable fabrication of active materials, including emerging compositions of LCE. Of note are 3D printable ionene LCE, which offer new ways to modulate electromechanical and thermomechanical coupling in LCE to broaden the palette of properties that can be harnessed in functional applications.