Self-assembly by polymer crystallization

A fortunate discovery led to the development of a novel thermoresponsive plasmonic sensor through the crystallization of a polymer grafted to gold nanoparticles. It turns out that storing polyethylene glycol (PEG) coated nanoparticles in pure ethanol results in the loss of their colloidal stability at room temperature. This was found to originate from the melting-crystallization behavior of the linear polymer, PEG. Upon heating above the phase transition temperature, the nanoparticles spontaneously disassembled and were well-dispersed as a beautiful wine-red color. Upon cooling below their crystallization temperature, the gold nanoparticles self-assembled into structures with differing degrees of long range order, giving the dispersion a purple color.

This self-assembly process can be tuned by a number of parameters, and led to the construction of a colloidal temperature sensor that presents either an irreversible or reversible switching behavior depending on the binding of metal cations. The potential for directed self-assembly through polymer crystallization is an intriguing area of research that the BioNanomaterials group is currently investigating for a variety of applications.

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