Two-Dimensional Crystallization of Poly(N-isopropylacrylamide)-Capped Gold Nanoparticles

Wang, Wenjie; Lawrence, Jack; Bu, Wei; Zhang, Honghu; Vaknin, David

Two-Dimensional Crystallization of Poly(N-isopropylacrylamide)-Capped Gold Nanoparticles

File

IS_J_9723.pdf (1.77 MB)

Date

2018-06-27

Authors

Wang, Wenjie

Lawrence, Jack

Bu, Wei

Zhang, Honghu

Vaknin, David

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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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Physics and Astronomy

Physics and astronomy are basic natural sciences which attempt to describe and provide an understanding of both our world and our universe. Physics serves as the underpinning of many different disciplines including the other natural sciences and technological areas.

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Materials Science and Engineering

Materials engineers create new materials and improve existing materials. Everything is limited by the materials that are used to produce it. Materials engineers understand the relationship between the properties of a material and its internal structure — from the macro level down to the atomic level. The better the materials, the better the end result — it’s as simple as that.

Department

Ames National LaboratoryPhysics and AstronomyMaterials Science and Engineering

Abstract

Surface-sensitive X-ray reflectivity and grazing incidence small-angle X-ray scattering reveal the structure of polymer-capped-gold nanoparticles (AuNPs that are grafted with poly(N-isopropylacrylamide); PNIPAM–AuNPs) as they self-assemble and crystallize at the aqueous suspension/vapor interface. Citrate-stabilized AuNPs (5 and 10 nm in nominal diameter) are ligand-exchanged by 6 kDa PNIPAM-thiol to form corona brushes around the AuNPs that are highly stable and dispersed in aqueous suspensions. Surprisingly, no clear evidence of thermosensitive effect on surface enrichment or self-assembly of the PNIPAM–AuNPs is observed in the 10–35 °C temperature range. However, addition of simple salts (in this case, NaCl) to the suspension induces migration of the PNIPAM–AuNPs to the aqueous surface, and above a threshold salt concentration, two-dimensional crystals are formed. The 10 nm PNIPAM–AuNPs form a highly ordered single layer with in-plane triangular structure, whereas the 5 nm capped NPs form short-range triangular structure that gradually becomes denser as salt concentration increases.