Materials Design guided by Defects in Liquid Crystals

Architected cellular materials represent a growing body of materials research encompassing a broad classification of materials, from open celled foams to sheet-based lattices. Comprised of unit cells of varying geometries and tessellation patterns, these material systems give rise to unique properties attributed primarily to their unit cell geometry as opposed to their bulk material chemistry. Enabled by additive manufacturing technologies, architected cellular materials are increasingly making their way into commercial design and production, offering solutions to many challenges faced by industries such as biomedicine and personal protective equipment and energy. However, additional barriers to ubiquity such as the stiffness/toughness tradeoff of lattice based architected cellular materials present opportunities for the development of novel unit cell geometries with tunable topological features. Current areas of design inspiration are drawn from the intricate patterns displayed by nature or solid atomistic crystals. However, the opportunity for novel approaches to unit cell design presents a frontier ripe for exploration.<br/><br/>One such approach exists in the study of the behavior of liquid crystals and their interpenetrating networks of defects or disclination lines. This fascinating state of matter possesses the long range orientational ordering of solid crystals while retaining the fluidlike properties and response to confining geometries possessed by liquids. These material systems exhibit self-assembly of their constituent molecules, or mesogens, into interesting mesostructures which pack together forming 3D periodic arrangements. This behavior has been extensively investigated for its optical response; however, little is understood about the mechanical properties of the resultant disclination architectures. Through utilization of Landau-de Gennes guided simulations, these architectures can be readily predicted at the nanoscale and then upscaled for design and fabrication as promising candidates for architected cellular materials. Of the unique geometries which arise from the disclination arrangements in liquid crystal systems, is the interpenetrating double diamond lattice that shows promise for structural applications. Study of the mechanical response of these geometries indicate potential toughening mechanisms induced by contact between the bicontinuous lattice networks. In addition to its variable strut diameter and reinforced nodal regions, the relative density of these structures can be adjusted rapidly using the liquid crystal’s scalar order parameter. The exploration of these disclination lattices offers a promising avenue for the enhancement of architected cellular materials, with tunable design parameters unique to the behavior of liquid crystal systems.