The integration of layer-by-layer (LbL) and self-assembly methods has the potential to achieve precision assembly of nanocomposite materials. Knowledge of how nanoparticles move across and within stacked materials is critical for directing nanoparticle assembly. Here, we investigate nanoparticle self-assembly within two different LbL architectures: (1) a bilayer composed of two immiscible polymer thin-films, and (2) a bilayer composed of polymer and graphene that possesses a “hard-soft” interface. Polymer-grafted silver nanocubes (AgNCs) are employed as a model nanoparticle system for systematic experiments – characterizing both assembly rate and resulting morphologies – that examine how assembly is affected by the presence of an interface. We observe that polymer grafts can serve to anchor AgNCs at the bilayer interface and to decrease particle mobility, or can promote particle transfer between layers. We also find that polymer viscosity and polymer mixing parameters can be used as predictors of assembly rate and behavior. These results provide a pathway for designing more complex multilayered nanocomposites.
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Tunable Orientation and Assembly of Polymer-Grafted Nanocubes at Fluid–Fluid Interfaces
Self-assembly of faceted nanoparticles is a promising route for fabricating nanomaterials; however, achieving low-dimensional assemblies of particles with tunable orientations is challenging. Here, we demonstrate that trapping surface-functionalized faceted nanoparticles at fluid–fluid interfaces is a viable approach for controlling particle orientation and facilitating their assembly into unique one- and two-dimensional superstructures. Using molecular dynamics simulations of polymer-grafted nanocubes in a polymer bilayer along with a particle-orientation classification method we developed, we show that the nanocubes can be induced into face-up, edge-up, or vertex-up orientations by tuning the graft density and differences in their miscibility with the two polymer layers. The orientational preference of the nanocubes is found to be governed by an interplay between the interfacial area occluded by the particle, the difference in interactions of the grafts with the two layers, and the stretching and intercalation of grafts at the interface. The resulting orientationally constrained nanocubes are then shown to assemble into a variety of unusual architectures, such as rectilinear strings, close-packed sheets, bilayer ribbons, and perforated sheets, which are difficult to obtain using other assembly methods. Our work thus demonstrates a versatile strategy for assembling freestanding arrays of faceted nanoparticles with possible applications in plasmonics, optics, catalysis, and membranes, where precise control over particle orientation and position is required.
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- Award ID(s):
- 2011924
- NSF-PAR ID:
- 10324271
- Date Published:
- Journal Name:
- ACS Nano
- ISSN:
- 1936-0851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Faceted nanoparticles can be used as building blocks to assemble nanomaterials with exceptional optical and catalytic properties. Recent studies have shown that surface functionalization of such nanoparticles with organic molecules, polymer chains, or DNA can be used to control the separation distance and orientation of particles within their assemblies. In this study, we computationally investigate the mechanism of assembly of nanocubes grafted with short-chain molecules. Our approach involves computing the interaction free energy landscape of a pair of such nanocubes via Monte Carlo simulations and using the Dijkstra algorithm to determine the minimum free energy pathway connecting key states in the landscape. We find that the assembly pathway of nanocubes is very rugged involving multiple energy barriers and metastable states. Analysis of nanocube configurations along the pathway reveals that the assembly mechanism is dominated by sliding motion of nanocubes relative to each other punctuated by their local dissociation at grafting points involving lineal separation and rolling motions. The height of energy barriers between metastable states depends on factors such as the interaction strength and surface roughness of the nanocubes and the steric repulsion from the grafts. These results imply that the observed assembly configuration of nanocubes depends not only on their globally stable minimum free energy state but also on the assembly pathway leading to this state. The free energy landscapes and assembly pathways presented in this study along with the proposed guidelines for engineering such pathways should be useful to researchers aiming to achieve uniform nanostructures from self-assembly of faceted nanoparticles.more » « less
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Surface functionalization of nanoparticles with polymer grafts was recently shown to be a viable strategy for controlling the relative orientation of shaped nanoparticles in their higher-order assemblies. In this study, we investigated in silico the orientational phase behavior of coplanar polymer-grafted nanocubes confined in a thin film. We first used Monte Carlo simulations to compute the two-particle interaction free-energy landscape of the nanocubes and identify their globally stable configurations. The nanocubes were found to exhibit four stable phases: those with edge–edge and face–face orientations, and those exhibiting partially overlapped slanted and parallel faces previously assumed to be metastable. Moreover, the edge–edge configuration originally thought to involve kissing edges instead displayed partly overlapping edges, where the extent of the overlap depends on the attachment positions of the grafts. We next formulated analytical scaling expressions for the free energies of the identified configurations, which were used for constructing a comprehensive phase diagram of nanocube orientation in a multidimensional parameter space comprising of the size and interaction strength of the nanocubes and the Kuhn length and surface density of the grafts. The morphology of the phase diagram was shown to arise from an interplay between polymer- and surface-mediated interactions, especially differences in their scalings with respect to nanocube size and grafting density across the four phases. The phase diagram provided insights into tuning these interactions through the various parameters of the system for achieving target configurations. Overall, this work provides a framework for predicting and engineering interparticle configurations, with possible applications in plasmonic nanocomposites where control over particle orientation is critical.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsnano.1c10416
