Many technological applications of nanoparticles rely on our ability to control the interactions of nanoparticles to exploit their ordered structures and collective properties. In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Prof. Yao Lin and his students at University of Connecticut are conducting studies to understand the physical mechanisms that make possible the controlled assembly in solution of nanoparticles with different types of molecules (ligands) grafted onto them, and to predict where the tendencies to aggregate further and to disperse are balanced so that equilibrium is reached. A goal is a general approach for prediction and control of the formation of bigger "supramolecular" structures from a large set of nanoparticles. Understanding the mechanism of the assembly process can contribute to the generation of hierarchical, multicomponent materials and systems, eventually approaching the level of sophistication found in nature. Using biologically inspired mechanisms to synthesize supramolecular structures provides new opportunities and challenges in chemical research and education. The PI aims to address students needs for interdisciplinary education and high quality research experience in this emerging field. The proposed research will be integrated into curriculum materials and outreach activities, providing interdisciplinary training and vibrant research experiences for students at different levels.
Intermolecular interactions define the self-assembly pathways and the kinetics of the formation of large-scale supramolecular structures. In nature, numerous globular proteins can be "polymerized" into specific helical or tubular assemblies via a well-defined nucleation-growth mechanism, as exemplified by the formation of actin filaments and microtubules. Inspired by the sophisticated assembly mechanism, the PI is developing a general strategy for controlled assembly of ligand-grafted, charged nanoparticles. Guided by a thermodynamic analysis, fibrous supramolecular structures assembled from polypeptide-grafted, charged nanoparticles have been successfully created in the preliminary study. Using these nanoparticles as a model system, the research focuses on: (1) conducting kinetic analysis to understand the nucleation mechanism involved in the fibrous supramolecular assembly of charged nanoparticles, and (2) determining the phase diagram for the self-association of charged nanoparticles and elucidating the transition mechanism between different supramolecular structures. By mimicking nature's assembly approaches, the research is developing a general strategy for assembling nanoparticle building blocks to predictable superstructures, and providing insights into the critical nucleation process that connects kinetic and equilibrium behaviors of nanoparticles self-associations. Particularly, the understanding of thermodynamic and kinetic processes involved in the fibrous assembly of nanoparticles tests the applicability of classic theories obtained from the studies of the protein polymerizations, leading to the need for development of a more generalized model.
