Programmable Colloid Assembly for Nanophotonics

Abstract

Colloidal nanoparticles offer a versatile platform for the design of photonic materials through programmable assembly. However, translating nanoscale control into large-area, scalable fabrication remains a persistent challenge, particularly for multifunctional optical devices operating across visible and infrared regimes. This dissertation presents a strategy for programmable colloidal assembly that bridges the gap between lab-scale photonic devices and scalable manufacturing, with broad implications for structural coloration, plasmonic engineering, and radiative thermal management. A proton-assisted electrostatic assembly process was developed to facilitate rapid, uniform deposition of charged nanoparticles onto diverse substrates. By adjusting the proton concentration in the solution, the electrostatic attraction between charged nanoparticles and the substrate can be significantly enhanced without requiring chemical modification. This method is compatible with various types of coating strategies, including roll-type, stencil printing, dip coating, all offering high-throughput, wafer-scale (or centimeter scale) transfer in seconds. Furthermore, the electrostatic nature of the assembly allows for site-selective patterning and autonomous defect healing, reinforcing its practicality in manufacturing settings. These findings establish a scalable, substrate-adaptive, and application-oriented colloidal assembly platform, addressing pressing societal needs such as personal thermal safety, outdoor visibility in low-light or hazardous environments, and passive climate adaptation, thereby contributing to a safer and more resilient human environment. To ensure outdoor visibility in dark environments, broadband plasmonic reflectors were fabricated by vertically assembling metallic nanoparticles on metallic mirrors. By tuning interparticle gaps and substrate interactions, simultaneous structural coloration, and near-infrared (NIR) reflectance were achieved. These broadband reflectors are particularly useful for outdoor signage and safety applications, where visual and machine-readable information must coexist. These reflectors exhibited enhanced durability under ultraviolet radiation, thermal cycling, and high humidity, indicating their suitability for outdoor optical applications. This thesis further extends assembly strategy to fabricate broadband scattering, spanning from visible to near-infrared regime, in conjunction with dielectric nano/microspheres. These coatings enable selective solar reflection and mid-infrared emission, providing passive radiative cooling functionalities. A wearable demonstration on human hair confirmed the platform’s practical potential, showing measurable body temperature regulation under natural sunlight without the need for external energy input.