Two-dimensional assembly of gold nanoparticles grafted with charged-end-group polymers

Hyeong Jin Kim; Binay P Nayak; Honghu Zhang; Benjamin M Ocko; Alex Travesset; David Vaknin; Surya K Mallapragada; Wenjie Wang

doi:10.1016/j.jcis.2023.07.095

Two-dimensional assembly of gold nanoparticles grafted with charged-end-group polymers

J Colloid Interface Sci. 2023 Nov 15;650(Pt B):1941-1948. doi: 10.1016/j.jcis.2023.07.095. Epub 2023 Jul 20.

Authors

Hyeong Jin Kim¹, Binay P Nayak¹, Honghu Zhang², Benjamin M Ocko³, Alex Travesset⁴, David Vaknin⁴, Surya K Mallapragada⁵, Wenjie Wang⁶

Affiliations

¹ Ames National Laboratory, and Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50011, United States.
² Center for Functional Nanomaterials and NSLS-II, Brookhaven National Laboratory, Upton, NY 11973, United States.
³ NSLS-II, Brookhaven National Laboratory, Upton, NY 11973, United States.
⁴ Ames National Laboratory, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, United States.
⁵ Ames National Laboratory, and Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50011, United States. Electronic address: suryakm@iastate.edu.
⁶ Division of Materials Sciences and Engineering, Ames National Laboratory, U.S. DOE, Ames, IA 50011, United States. Electronic address: wenjiew@ameslab.gov.

PMID: 37517193
DOI: 10.1016/j.jcis.2023.07.095

Abstract

Hypothesis: Introducing charged terminal groups to polymers that graft nanoparticles enable Coulombic control over their assembly by tuning the pH and salinity of their aqueous suspensions.

Experiments: Gold nanoparticles (AuNPs) are grafted with poly (ethylene glycol) (PEG) terminated with (charge-neutral), (negatively charged) or groups (positively charged), and characterized with dynamic light scattering, ζ-potential, and thermal gravimetric analysis. Liquid surface X-ray reflectivity (XR) and grazing incidence small-angle X-ray scattering (GISAXS) are used to determine the density profile and in-plane structure of the AuNPs assembly at the aqueous surface.

Findings: Assembly of PEG-AuNPs at the liquid/vapor interface is tunable by adjusting pH or salinity for COOH but less for terminals. The distinct assembly behaviors are attributed to the overall charge of PEG-AuNPs as well as PEG conformation. COOH-PEG corona is more compact than those of the other terminal groups, leading to a crystalline structure with a smaller superlattice. The net charge per particle depends not only on the PEG terminal groups but also on the cation sequestration of PEG and the intrinsic negative charge of the AuNP surface. [1] The closeness to overall charge neutrality, and hydrogen bonding in play, brought by -PEG, drive -PEG-AuNPs to assembly and crystallinity without additives to the suspensions.