VISUALIZING DYNAMICS DURING CHEMICAL REACTION DRIVEN NON – EQUILIBRIUM COLLOIDAL AND NANOPARTICLE ASSEMBLY

Abstract

Biological nano and microstructures exist far from thermodynamic equilibrium by continuous consumption of energy that allows them to reconfigure or adapt to changes in the local environment. Utilization of these non-equilibrium structure formation processes in synthetic colloidal particle and nanoparticle (NP) systems is expected to enable unprecedented control over the dynamics of synthetic active soft materials and systems that are beyond the reach of equilibrium self – assembly. In this work we adapted two non – equilibrium structure formation processes observed in biological systems, dissipative assembly and reaction diffusion instability, to generate dynamic colloidal assemblies and self-organized patterns of nanoparticles. First, we investigated how the surface chemistry and interparticle interactions between colloids changed during chemical reaction driven dissipative assembly of polystyrene colloids. A key result was the first, time dependent measurements of the dynamic colloid surface chemistry (surface charge and hydrophobicity) during dissipative assembly. Importantly, we demonstrated that thermodynamic interparticle interaction models typically used for equilibrium self-assembly are effective in describing fuel driven colloid assembly far from equilibrium. The interparticle interaction models demonstrated that electrostatic interactions controlled the concentration of particle aggregates while the strength of hydrophobic interactions determined whether colloids underwent irreversible aggregation or dissipative assembly. Next, using a correlative fluorescence microscopy and liquid phase transmission electron microscopy (LPTEM) method, we demonstrated that aminated polymer capping ligands on metal NPs undergo crosslinking and chain scission reactions as a result of formation of hydroxyl and hydrogen radicals due to electron beam induced radiolysis of water. We demonstrated that a hydroxyl radical scavenger can minimize the electron beam induced reactions in the polymers. Based on this fundamental knowledge, we introduced an instability to an initially homogenous gold NP decorated aminopolysiloxane thin film immersed in water by scanning TEM beam. Radiolysis driven polymer radical reactions of polysiloxane coupled with diffusion of radicals, polymers, and NPs caused the polymer and NP to self-organize into repeating spatial patterns, i.e., Turing patterns, with no template or specific interparticle interactions. Spots, strings and labyrinth patterns that closely resembled Turing skin pigmentation patterns on various animals were obtained by tuning the chemistry of the system. A series of systematic experiments identified that hydroxyl radicals and NPs as critical species driving the formation of the NP patterns. We expect this work could be used as a model system in establishing design rules for nanoscale pattern formation by reaction – diffusion instability.