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

Abstract

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. DisciplinesCondensed Matter Physics | Nanoscience and Nanotechnology 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., Cs 2 SO 4 ) 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.

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

“…Thus, the results presented here are from PNIPAM-AuNPs in salt (NaCl) solutions and performed at room temperature i.e., 22 • C. ED. This is also consistent with the surface ED profiles determined for aqueous surface superlattices of PEG-AuNPs that are induced by salts 10,12 . The asymmetry of the film ED (different widths at the vapor and liquid interfaces) and a small step like at the film/gas interface suggest that the PNIPAM polymers around the AuNPs are at different states at the two interfaces, i.e., those close to the gas phase are highly compressed and concentrated while those in proximity of the fluid are loosely packed and extended into the subphase.…”

“…7 The aqueous bi-phase phenomena of these non-ionic polymers has since been exploited for a variety of application most notably for isolating and concentrating biomaterials. 8,9 Recently, the bi-phasic separation has been been successfully used for self-assembly and crystallization of PEG capped nanoparticles at vaporsuspension interfaces by adjusting salt concentrations [10][11][12][13] . Furthermore, sufficiently high salt concentrations induce three dimensional crystalline precipitates as has been observed in small angle X-ray scattering studies.…”

Stabilizing Colloidal Particles against Salting-out by Shortening Surface Grafts

“…The particle core is composed of heptafluorobutyl methacrylate (HFBMA) polymer and the shell of poly(ethylene glycol) polymers with acrylate and methoxy end groups (mPEGA). Furthermore, the particles are considerably larger than the gold nanoparticles studied by Vaknin and coworkers [21,22,23,24] resulting in 1.1. Purpose a PEG-shell that is a much smaller part of the overall core-shell particle.…”

“…Furthermore, in the interfacial activity studies, the particles have an opportunity to escape the worsened aqueous solvent by moving to the interface or even the oil phase. Indeed, nanoparticles grafted with PEG have been found to be surface active [95,96,97,98,22,23,21,24]. It has also been shown, via computer simulations, that the grafted polymers on nanoparticles at liquid-liquid and liquid-air interfaces deform [99,100].…”

“…Recently, Vaknin and coworkers examined yet another possible explanation for the instability of PEG-grafted gold nanoparticles in a number of papers [21,22,23,24]. They discovered that the polymer-grafted gold nanoparticles were surface active, spontanously creating a monolayer at the air-water surface.…”