Ionic depletion at the crystalline Gibbs layer of PEG-capped gold nanoparticle brushes at aqueous surfaces

In situ surface-sensitive x-ray diffraction and grazing incidence x-ray fluorescence spectroscopy (GIXFS) methods are combined to determine the ionic distributions across the liquid/vapor interfaces of thiolatedpolyethylene-glycol–capped gold nanoparticle (PEG-AuNP) solutions. Induced by the addition of salts (i.e., Cs2SO4) to PEG-AuNPs solutions, two-dimensional hexagonal lattices of PEG-AuNPs form spontaneously at the aqueous surfaces, as is demonstrated by x-ray reflectivity and grazing incidence small-angle x-ray scattering. By taking advantage of element specificity with the GIXFS method, we find that the cation Cs+ concentration at the crystalline film is significantly reduced in parts of the PEG-AuNP film compared with that in the bulk. Disciplines Condensed Matter Physics | Nanoscience and Nanotechnology This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_manuscripts/90 PHYSICAL REVIEW MATERIALS 1, 076002 (2017) Ionic depletion at the crystalline Gibbs layer of PEG-capped gold nanoparticle brushes at aqueous surfaces Wenjie Wang,1 Honghu Zhang,2 Surya Mallapragada,3 Alex Travesset,4 and David Vaknin4,* 1Division of Materials Sciences and Engineering, Ames Laboratory, U.S. DOE, Ames, Iowa 50011, USA 2Ames Laboratory and Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA 3Ames Laboratory and Department of Chemical and Biological Engineering, Iowa State University, Ames, Iowa 50011, USA 4Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA (Received 18 May 2017; revised manuscript received 6 September 2017; published 14 December 2017) In situ surface-sensitive x-ray diffraction and grazing incidence x-ray fluorescence spectroscopy (GIXFS) methods are combined to determine the ionic distributions across the liquid/vapor interfaces of thiolatedpolyethylene-glycol–capped gold nanoparticle (PEG-AuNP) solutions. Induced by the addition of salts (i.e., Cs2SO4) to PEG-AuNPs solutions, two-dimensional hexagonal lattices of PEG-AuNPs form spontaneously at the aqueous surfaces, as is demonstrated by x-ray reflectivity and grazing incidence small-angle x-ray scattering. By taking advantage of element specificity with the GIXFS method, we find that the cation Cs+ concentration at the crystalline film is significantly reduced in parts of the PEG-AuNP film compared with that in the bulk. DOI: 10.1103/PhysRevMaterials.1.076002