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

Journal Article · Sun Dec 15 00:00:00 EST 2019 · Langmuir

DOI:https://doi.org/10.1021/acs.langmuir.9b02966· OSTI ID:1593153

Wang, Wenjie  ^[1]; Kim, Hyeong Jin ^[1]; Bu, Wei ^[2]; Mallapragada, Surya  ^[1]; Vaknin, David  ^[1]

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1. Ames Lab., Ames, IA (United States)
2. Univ. of Chicago, IL (United States)

We use synchrotron X-ray reflectivity and grazing incidence small-angle X-ray scattering to investigate the surface assembly of the poly(ethylene 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 θ-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 nonspherical shaped complex that, although packs at high density, cannot organize into a 2D ordered arrangement.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-07CH11358; NSF/CHE-1834750; AC02-06CH11357
• OSTI ID: 1593153
• Report Number(s): IS-J-10138
• Journal Information: Langmuir, Vol. 36, Issue 1; ISSN 0743-7463
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY