RUI: Photothermal Self-assembly for Understanding Non-equilibrium Crystallization, Tunable Phases, and Reconfigurable Shapes

About This Grant

Non-technical abstract: This project will investigate how microscopic particles respond to light and organize themselves into materials with tunable properties. Prior studies on self-assembly helped us understand the formation of different phases in equilibrium conditions in the absence of any external energy provided to the material. If the building block particles receive energy from an external source, self-assembled structures can form rapidly and exhibit dynamic properties that are not currently well understood. The PIs and the students will perform laboratory experiments and develop computational models to elucidate how different structures and phases emerge under light-driven assembly conditions. The project activities will be carried out by students in a primarily undergraduate university with a large population of first-generation college students. The project will reduce the barrier to STEM education for non-scientists by recruiting students from different academic backgrounds, introducing research-related topics into the undergraduate curriculum, and designing an interactive nanoparticle demo for K-12 students. Technical abstract: The team will employ a binary mixture of plasmonic nanoparticles and assembly building block particles to design photothermal self-assembly experiments. Light absorption by the plasmonic nanoparticles causes a temperature gradient and convection flow in a colloidal suspension that can assemble the larger building block particles into a monolayer. The first objective of the project is to develop an in-depth understanding of crystallization under nonequilibrium conditions. The team will identify the critical conditions for fluid-to-solid phase transitions and estimate the pseudo-pair potential in assemblies with different particle sizes. A computational model will be developed to understand the impact of the active plasmonic nanoparticles on the assembly of the larger building block particles. Crystal nucleation, growth, and coarsening dynamics will be quantified for particles with different sizes. The second objective is to understand how different phases (colloidal crystal, gel, liquid, and glass) emerge from the interplay between hydrodynamic and electrostatic interactions between particles. With this goal, assemblies with different ratios of the two particle sizes, number densities, and charge densities will be investigated in experiments and computational models. The final objective is to examine whether patterned light illumination can be employed to cause a transition between two self-assembled shapes. Particle and defect dynamics during shape reconfiguration will be quantified in shape-reconfiguration experiments performed on crystalline and dense fluid phases. Insights gained from the experiments could potentially lead to the design of colloidal grippers that can hold and transport microscopic objects. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.