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We report the results of grazing incidence X-ray diffraction (GIXD) measurements from water supported Langmuir monolayers of gold nanoparticles ligated with dodecanethiol (12 carbons), tetradecanethiol (14 carbons), hexadecanethiol (16 carbons), and octadecanethiol (18 carbons). These monolayers are formed from solutions with varying concentrations of the respective thiols. We show that equilibrium between adsorbed thiol molecules and the thiols in the bulk solution implies fractional coverage of the Au nanoparticle core. We also show that the nanoparticle–nanoparticle separation and the correlation length of particles in these ordered films increases with thiol concentration in the parent solution, and that excess thiol can be found in the space between particles as well as in islands away from the particles. Using the equilibrium constant relating ligand solution concentration and nanoparticle surface coverage of the gold core by the ligand molecules, we interpret the way in which varying thiol concentration affects the nanoparticle–nanoparticle separation as a function of surface coverage of the gold core by the ligand molecules.
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This content will become publicly available on November 6, 2025
Size-Dependent Electrostatic Adsorption of Polymer-Grafted Gold Nanoparticles on Polyelectrolyte Brushes
Designing a functional surface that selectively adsorbs nanoparticles based on their size and shape is essential for developing an advanced adsorption-based, post-synthesis nanoparticle separation device. We demonstrate selective adsorption of larger nanoparticles from solution onto a polyelectrolyte brush by tuning the salt concentration. Specifically, a positively-charged polyelectrolyte brush is created by converting pyridine groups of poly(2-vinylpyridine) to n-methyl pyridinium groups using methyl iodide. The adsorption kinetics and thermodynamics of polyethylene glycol-grafted, negatively charged gold nanoparticles (diameters of 12 and 20 nm) were monitored as a function of salt concentration. In a salt-free solution, the polyelectrolyte brush adsorbs gold nanoparticles of both sizes. As the salinity increases, the areal number density of adsorbed nanoparticles monotonically decreases and becomes negligible at high salinity. Interestingly, there is an intermediate range of salt concentrations (i.e., 15 – 20 mM of NaCl) where the decrease in nanoparticle adsorption is more pronounced for smaller particles, leading to size-selective adsorption of the larger nanoparticles. As a further demonstration of selectivity, the polyelectrolyte brush is immersed in a binary mixture of 12-nm and 20-nm nanoparticles and found to selectively capture larger particles with ~ 90 % selectivity. In addition, the size distribution of as-synthesized gold nanoparticles, with an average diameter of 12 nm, was reduced by selectively removing larger particles by exposing the solution to polyelectrolyte brush surfaces. This study demonstrates the potential of a polyelectrolyte brush separation device to remove larger nanoparticles by controlling electrostatic interactions between polymer brushes and particles
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- Award ID(s):
- 2034122
- PAR ID:
- 10554868
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS Applied Materials & Interfaces
- Volume:
- 16
- Issue:
- 44
- ISSN:
- 1944-8244
- Page Range / eLocation ID:
- 61083 to 61095
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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