Coexistence and Phase Behavior of Solvent–Polystyrene-Grafted Gold Nanoparticle Systems

Abstract

Polymer-grafted nanoparticles (PGNs) are widely used as additives or as single-component assemblies in numerous technologies, spanning from composites and coatings to membranes, optical elements, and printable electronics. How the design modularity of PGNs relates to their dispersibility and morphology in thermal or poor solvents, however, is not well established. Herein, we provide experimental volume fraction (ϕ)−temperature (T) coexistence curves (ϕ CE and T CE ) for polystyrene-grafted gold nanoparticles (PS-AuNPs) in solvents of various qualities (cyclohexane, cyclopentane, and ethyl acetate) using a combination of UV−vis spectroscopy and small-angle X-ray scattering. These systems exhibit upper critical solution temperatures, with coexistence curves that are broader and shifted to lower temperatures relative to their polymer analogs, consistent with prior reports of the impact of macromolecular branching. The coexistence curves span over 6 orders of magnitude in concentration, exhibit solvent-rich and solvent-poor arms that are ϕ PGN -dependent, display a reduction in critical temperature (T C *) as graft molecular weight decreases, exhibit an overall narrowing of the solvent-poor arm at higher graft molecular weights, and reveal a minimal influence of core nanoparticle volume (900−4200 nm 3 ). Additionally, the structure within the solvent swollen PS-AuNPs aggregates is disordered or face-centered cubic and depends on the aggregation temperature relative to T C * than on solvent characteristics. Such quantification of PGN phase behavior in thermal or poor solvents is used to demonstrate thermal fraction for purification and will inform future synthesis methods, self and directed assembly techniques, film and fiber processing, and formulation of inks, adhesives, thermosets, and coatings.

Depletion-Driven Assembly of Polymer-Coated Nanocrystals

“…In contrast, cloudy samples exhibit a degree of ordering indicating assembly: a sharp, primary peak emerges. The suppression of scattering intensity at slightly lower q values than this peak, a correlation hole, is typical for phase separating systems as correlations in the concentrated phase develop. , Phase boundaries were determined via visual inspection, and corroborated with SAXS, for each of several NC volume fractions and concentrations of PEG depletant (Figure c).…”

Depletion-driven assembly of polymer-coated nanocrystals

“…systems as correlations in the concentrated phase develop. 84,85 Phase boundaries were determined via visual inspection, and corroborated with SAXS, for each of several NC volume fractions and concentrations of PEG depletant (Figure 2c).…”

Formation of kinetically trapped small clusters of PEGylated gold nanoparticles revealed by the combination of small-angle X-ray scattering and visible light spectroscopy

“…4,[16][17][18] It is important to note that this clustering approach differs substantially from creating ab ovo unstable systems or aggregation schemes relying on (macro)molecular linkers, 8,19 but belongs to the broader family of solvent quality tuning based aggregation approaches. 6,7,20 In this work, we aimed to investigate the development of nanoparticle clusters, where the driving force for clustering is rather moderate, favoring the formation of smaller particle aggregates. We investigated the assembly of PEGylated nanoparticles by a combined SAXS and visible light spectroscopy approach in order to consistently link these independent measurement results to the structural changes.…”

“…4,5 One straightforward way to tune the aggregation is by controlled reduction of solvent quality in surface-grafted polymer-stabilized nanoparticle systems. 6,7 On the other hand, depending on the structure of the cluster and on the distance between the particles within the clusters, the resulting optical spectrum can have markedly different characteristics. When only a few particles participate in forming the clusters and/or their structure is well defined, the resulting optical changes can be well interpreted with the help of optical calculations.…”

“…4,16–18 It is important to note that this clustering approach differs substantially from creating ab ovo unstable systems or aggregation schemes relying on (macro)molecular linkers, 8,19 but belongs to the broader family of solvent quality tuning based aggregation approaches. 6,7,20…”