Campus Units

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

Document Type

Article

Research Focus Area

Advanced and Nanostructured Materials

Publication Version

Submitted Manuscript

Publication Date

1-14-2020

Journal or Book Title

Langmuir

Volume

36

Issue

1

First Page

311

Last Page

317

DOI

10.1021/acs.langmuir.9b02966

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.

Comments

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Langmuir, copyright © American Chemical Society after peer review. To access the final edited and published work see DOI: 10.1021/acs.langmuir.9b02966. Posted with permission.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

2020-MallapragadaSurya-UnusualEffectIodine-SI.pdf (3336 kB)
Supporting Information

Published Version

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