## Ames Laboratory Accepted Manuscripts

#### Title

Unusual Effect of Iodine Ions on the Self-Assembly of Poly(ethylene glycol)-Capped Gold Nanoparticles

1-14-2020

#### Department

Chemical and Biological Engineering; Physics and Astronomy; Ames Laboratory; Neuroscience; Materials Science and Engineering

#### Campus Units

Ames Laboratory, Chemical and Biological Engineering, Materials Science and Engineering, Physics and Astronomy, Neuroscience

1593153

IS-J 10138

#### DOI

10.1021/acs.langmuir.9b02966

Langmuir

36

1

311

317

#### Abstract

We use synchrotron X-ray reflectivity and grazing incidence small-angle X-ray scattering to investigate the surface assembly of the polyethylene glycol (PEG) grafted gold nanoparticles (PEG-AuNPs) induced by different salts. We find that NaCl and CsCl behave as many other electrolytes, namely drive the PEG-AuNPs to the vapor/suspension interface to form a layer of single particle depth and organize them into very high quality two-dimensional (2D) hexagonal crystals. By contrast, NaI induces the migration of PEG-AuNPs to the aqueous surface at much higher surface densities than the other salts (at similar concentrations). The resulting 2D ordering at moderate NaI concentrations is very short-ranged and at a higher NaI concentration the high density monolayer is amorphous. Considering NaCl, CsCl and the majority of salts behave similarly, this implicates the anomaly of iodine ion (I$^-$) in this unusual surface population. We argue that the influence of most electrolytes on the PEG corona preserves the polymer in the $\theta$-point with sufficient flexibility to settle into a highly ordered state, whereas I$^-$ has a much more severe effect on the corona by collapsing it. The collapsed PEG renders the grafted AuNP a non-spherical shaped complex that, although packs at high density, cannot organize into a 2D ordered arrangement.

#### DOE Contract Number(s)

AC02-07CH11358; NSF/CHE-1834750; AC02-06CH11357

en

#### Department of Energy Subject Categories

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

#### Publisher

Iowa State University Digital Repository, Ames IA (United States)

IS-J 10138 SI.pdf (3331 kB)
Supplementary Information

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