Depletion-driven assembly of polymer-coated nanocrystals




Green, Allison M.
Kadulkar, Sanket
Sherman, Zachary M.
FitzSimons, Thomas M.
Ofosu, Charles K.
Yan, Jiajun
Zhao, David
Ilavsky, Jan
Rosales, Adrienne M.
Helms, Brett A.

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Depletion-driven assembly has been widely studied for micron-sized colloids, but

questions remain at the nanoscale where the governing physics are impacted by the

stabilizing surface ligands or wrapping polymers, whose length scales are on the same

order as those of the colloidal core and the depletant. Here, we probe how wrapping

colloidal tin-doped indium oxide nanocrystals with polymers affects their depletion-

induced interactions and assembly in solutions of polyethylene glycol. Copolymers of

polyacrylic acid grafted with polyethylene oxide provide nanocrystal wrappings with

different effective polymer graft densities and molecular weights. (Ultra) small angle

X-ray scattering, coarse-grained molecular dynamics simulation, and molecular thermo-

dynamic theory were combined to analyze how depletant size and polymer wrapping

characteristics affect depletion interactions, structure, and phase behavior. The re-

sults show how depletant molecular weight, as well as surface density and molecular

weight of polymer grafts, set thresholds for assembly. These signatures are unique to

depletion-driven assembly of nanoscale colloids and mirror phase behaviors of grafted

nanoparticle–polymer composites. Optical and rheological responses of depletion-driven

assemblies of nanocrystals with different polymer shell architectures were probed to

learn how their structural differences impact properties. We discuss how these han-

dles for depletion-driven assembly at the nanoscale may provide fresh opportunities for

designing responsive depletion interactions and dynamically reconfigurable materials.



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Green AM, Kadulkar S, Sherman ZM, Fitzsimons TM, Ofosu CK, Yan J, et al. Depletion-driven assembly of polymer-coated nanocrystals. ChemRxiv. 2022; doi:10.26434/chemrxiv-2022-wzwnm