Thermofluidic Nonequilibrium Assembly of Reconfigurable Functional Structures.

Controlled assembly of functional structures that can be dynamically reconfigured remains a significant challenge in materials science. Here, we demonstrate a nonequilibrium assembly approach where colloidal particles organize into three-dimensional crystalline structures through the interplay of three temperature-induced phenomena: thermophoresis, thermoosmosis, and depletion forces from polyethylene glycol molecules. Using precisely controlled laser-induced temperature gradients, we assemble highly ordered colloidal crystals within minutes, significantly faster than conventional equilibrium approaches. These structures exhibit tunable photonic stopbands that can be modulated by adjusting the laser power, causing structural transitions between crystalline and toroidal configurations. By quantifying the underlying particle fluxes and growth dynamics, we develop a model that accurately predicts assembly rates across different conditions. Our thermofluidic assembly approach offers a versatile platform for creating reconfigurable functional materials with dynamically tunable properties, circumventing limitations of traditional equilibrium assembly methods.