Templated self-assembly of gold nanoparticles in smectic liquid crystals confined at 3D printed curved surfaces

The fabrication of assembled structures of topological defects in liquid crystals (LCs) has attracted much attention during the last decade, stemming from their potential applications in modern technologies, including photonic devices, tunable optical elements, and soft actuators. A range of techniques can be employed to create large areas of engineered defects in LCs, including mechanical shearing, chemical surface treatment, external fields, or geometric confinement. 3D printing has recently emerged as a powerful technique for fabricating novel patterning topographies, particularly enabling the confinement of LCs in geometries with curved surfaces that are challenging to achieve with conventional microfabrication methods. In this work, we show the advantages of using 3D-printed curved surfaces and controlled anchoring properties to confine LCs and engineer new structures of topological defects, whose structure we elucidate by comparison with a novel application of Landau-de Gennes free energy minimization to the smectic A-nematic phase transition. We also demonstrate the ability of these defects to act as a scaffold for assembling gold (Au) nanoparticles (NPs) into reconfigurable 3D structures. We discuss the characteristics of this templated self-assembly (TSA) approach and explain the relationship between NP concentrations and defect structures, with insights gained from numerical modeling. This work paves the way for a versatile platform for LC defect-templated assembly of functional nanomaterials, with potential applications in energy technology, including next-generation solar cells, tunable metamaterials, and energy-efficient optical devices.