Poly(N-isopropylacrylamide)-grafted gold nanoparticles at the vapor/water interface

Samuel Minier; Hyeong Jin Kim; Jonathan Zaugg; Surya K Mallapragada; David Vaknin; Wenjie Wang

doi:10.1016/j.jcis.2020.11.080

Poly(N-isopropylacrylamide)-grafted gold nanoparticles at the vapor/water interface

J Colloid Interface Sci. 2021 Mar:585:312-319. doi: 10.1016/j.jcis.2020.11.080. Epub 2020 Nov 27.

Authors

Samuel Minier¹, Hyeong Jin Kim², Jonathan Zaugg¹, Surya K Mallapragada², David Vaknin³, Wenjie Wang⁴

Affiliations

¹ Division of Materials Sciences and Engineering, Ames Laboratory, U.S. DOE, Ames, IA 50011, United States.
² Ames Laboratory, and Department of Chemical and Biological Engineering, Iowa State University, Ames, IA 50011, United States.
³ Ames Laboratory, and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, United States. Electronic address: vaknin@ameslab.gov.
⁴ Division of Materials Sciences and Engineering, Ames Laboratory, U.S. DOE, Ames, IA 50011, United States. Electronic address: wenjiew@ameslab.gov.

PMID: 33307304
DOI: 10.1016/j.jcis.2020.11.080

Abstract

Hypothesis: Grafting nanoparticles surfaces with water-soluble polymers modify interparticle interactions that are pivotal for assembling them into ordered phases. By manipulating salt concentrations of gold nanoparticles (AuNPs) that are grafted with poly(N-isopropylacrylamide) (PNIPAM-AuNPs), we hypothesize that various aggregated phases form at the suspension/vapor interface or in the bulk that depend on the molecular weight (MW) of PNIPAM and on salt concentrations.

Experiments: AuNPs are grafted with thiolated PNIPAM of molecular weights of 3 or 6 kDa, and grafting is confirmed by dynamic light scattering. Liquid-surfaces X-ray reflectivity and grazing incidence small-angle X-ray scattering are used to determine the density profiles of the suspension/vapor interface and their inplane structure as salt is added to the suspensions.

Findings: We find that surface enrichment is induced by adding NaCl to the suspensions, and that at low salt concentrations, the monoparticle layer formed is dispersed, and above a threshold salt concentration, depending on MW of PNIPAM, the PNIPAM-AuNPs order in a hexagonal structure. We show that the lattice constant of the two-dimensional hexagonal structure varies with salt concentration, and more significantly with MW of PNIPAM.

Keywords: Grazing incidence small angle X-ray scattering (GI-SAXS); Interfacial superlattice; PNIPAM-grafted nanoparticles; X-ray reflectivity.