Plasmonic
metal oxide nanocrystals are interesting electrochromic
materials because they display high modulation of infrared light,
fast switching kinetics, and durability. Nanocrystals facilitate solution-based
and high-throughput deposition, but typically require handling hazardous
nonaqueous solvents and further processing of the as-deposited film
with energy-intensive or chemical treatments. We report on a method
to produce aqueous dispersions of tin-doped indium oxide (ITO) by
refunctionalizing the nanocrystal surface, previously stripped of
its native hydrophobic ligands, with a hydrophilic poly(acrylic acid)
polymer featuring a low density of methoxy-terminated poly(ethylene
oxide) grafts (PAA-mPEO4). To determine conditions favoring
the adsorption of PAA-mPEO4 on ITO, we varied the pH and
chemical species present in the exchange solution. The extent of polymer
wrapping on the nanocrystal surface can be tuned as a function of
the pH to prevent aggregation in solution and deposit uniform, smooth,
and optical quality spray coated thin films. We demonstrate the utility
of polymer-wrapped ITO nanocrystal thin films as an electrochromic
material and achieve fast, stable, and reversible near-infrared modulation
without the need to remove the polymer after deposition provided that
a wrapping density of ∼20% by mass is not exceeded.