Here, we use Liquid-Phase Electron Microscopy (LP-EM) to detect out of equilibrium behavior of PS-b-PAA self-assemblies. LP-EM enables the study of short lived transitions providing mechanistic details of particle transformations in real time at the nanoscale. PS-b-PAA block copolymers with varying molecular weights were prepared using reversible addition-fragmentation transfer (RAFT) in two steps. Initially the polytert-butyl acrylate block was synthesized following a chain extension using styrene to afford PS-b-PtBuA. Tert-butyl ester groups were then hydrolyzed using trifluoroacetic acid in dichloromethane yielding PS-b-PAA block copolymer. PS-b-PAA micelles have previously been shown to achieve thermodynamic equilibrium in THF/Dioxane and water mixtures, where the micelles can reversibly reorganize into vesicles of increasing size by increasing the water concentration. These morphological transitions are currently thought to have particle fusion/fission like mechanisms. Initial Dynamic Light Scattering (DLS) measurement indicated non-quantitative change in particle size, which led us to study this system further. Using Transmission Electron Microscopy (TEM) and LP-EM, we investigated the thermodynamic and kinetic properties of these particles and provide mechanistic insight into particle transformations. Lastly, the relaxation times of these assemblies were measured along with the transformation efficiency upon changing the water concentration. Using the new mechanistic insights we aim to design new self-assembled structures based on manipulations to the thermodynamic and kinetic pathways.

Visualizing out of equilibrium behavior of polystyrene-block-poly(acrylic acid) (PS-PAA) self-assembled structures using liquid-phase electron microscopy

2019 Fall National Meeting

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