Switching Between Crystallization and Amorphous Agglomeration of Alkyl Thiol-Coated Gold Nanoparticles

Geyer, Tihamér; Born, Philip; Kraus, Tobias

doi:10.1103/physrevlett.109.128302

Cited by 42 publications

(53 citation statements)

References 25 publications

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“…Our most general finding -that ligand ordering can induce attraction between particles in solution -is nonetheless consistent with recent experimental results for Au nanoparticles coated with C 12 -C 18 alkanethiol ligands in n-heptane solvent. 54,55 In that study reversible aggregation was observed upon cooling and heating, 55 while an optimal temperature region was found for the formation of ordered crystalline aggregates when the aggregation was driven by the addition of a poor polar solvent. 54 Such optimum assembly often marks the boundary of thermodynamic stability for the assembled state.…”

Section: Discussionmentioning

confidence: 93%

“…54,55 In that study reversible aggregation was observed upon cooling and heating, 55 while an optimal temperature region was found for the formation of ordered crystalline aggregates when the aggregation was driven by the addition of a poor polar solvent. 54 Such optimum assembly often marks the boundary of thermodynamic stability for the assembled state. 56 If nanoparticle aggregation were driven by ligand ordering, we would thus expect conditions of optimal assembly to track equilibrium coexistence curves for the respective pure alkanes and alkanethiol ligands on dry nanoparticles.…”

Section: Discussionmentioning

confidence: 93%

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Ligand-Mediated Interactions between Nanoscale Surfaces Depend Sensitively and Nonlinearly on Temperature, Facet Dimensions, and Ligand Coverage

Widmer‐Cooper

Geissler

2016

ACS Nano

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Nanoparticles are often covered in ligand monolayers, which can undergo a temperature-dependent order-disorder transition that switches the particle-particle interaction from repulsive to attractive in solution. In this work, we examine how changes in the ligand surface coverage and facet dimensions affect the ordering of ligands, the arrangement of nearby solvent molecules, and the interaction between ligand monolayers on different particles. In particular, we consider the case of strongly bound octadecyl ligands on the (100) facet of CdS in the presence of an explicit n-hexane solvent. Depending on the facet dimensions and surface coverage, we observe three distinct ordered states that differ in how the ligands are packed together, and which affect the thickness of the ligand shell and the structure of the ligand-solvent interface. The temperature dependence of the order-disorder transition also broadens and shifts to lower temperature in a nonlinear manner as the nanoscale is approached from above. We find that ligands on nanoscale facets can behave very similarly to those on macroscopic surfaces in solution, and that some facet dimensions affect the ligand alignment more strongly than others. As the ligands order, the interaction between opposing monolayers becomes attractive, even well below full surface coverage. The strength of attraction per unit surface area is strongly affected by ligand coverage, but only weakly by facet width. Conversely, we find that bringing two monolayers together just above the order-disorder transition temperature can induce ordering and attraction.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 93%

Ligand-Mediated Interactions between Nanoscale Surfaces Depend Sensitively and Nonlinearly on Temperature, Facet Dimensions, and Ligand Coverage

Widmer‐Cooper

Geissler

2016

ACS Nano

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“…3D). This reconstruction typically increases the "stickiness" of NPs, promoting formation of amorphous solids (122,123).…”

Section: Nonadditivity At the Nanoscalementioning

confidence: 99%

Nonadditivity of nanoparticle interactions

Batista

Larson

Kotov

2015

Science

442

240

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Understanding interactions between inorganic nanoparticles (NPs) is central to comprehension of self-organization processes and a wide spectrum of physical, chemical, and biological phenomena. However, quantitative description of the interparticle forces is complicated by many obstacles that are not present, or not as severe, for microsize particles (μPs). Here we analyze the sources of these difficulties and chart a course for future research. Such difficulties can be traced to the increased importance of discreteness and fluctuations around NPs (relative to μPs) and to multiscale collective effects. Although these problems can be partially overcome by modifying classical theories for colloidal interactions, such an approach fails to manage the nonadditivity of electrostatic, van der Waals, hydrophobic, and other interactions at the nanoscale. Several heuristic rules identified here can be helpful for discriminating between additive and nonadditive nanoscale systems. Further work on NP interactions would benefit from embracing NPs as strongly correlated reconfigurable systems with diverse physical elements and multiscale coupling processes, which will require new experimental and theoretical tools. Meanwhile, the similarity between the size of medium constituents and NPs makes atomic simulations of their interactions increasingly practical. Evolving experimental tools can stimulate improvement of existing force fields. New scientific opportunities for a better understanding of the electronic origin of classical interactions are converging at the scale of NPs.

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“…This is consistent with the fact that gold nanoparticles typically form ordered superlattices with face-centered cubic (fcc), hexagonal close-packed (hcp), or body-centered cubic (bcc) structures. 12,13 Gold nanoparticles are, however, known to form amorphous agglomerates as a function of ligand length, temperature, and solvent quality, 18,19 suggesting that interaction anisotropy may not be negligible. One possible source of anisotropy is faceting, 20 but in the presence of a relatively mobile layer of passivating ligands, very careful control of nanoparticle shape and ligand-solvent chemistry a) Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Fluctuation-driven anisotropy in effective pair interactions between nanoparticles: Thiolated gold nanoparticles in ethane

Jabes

Yadav

Kumar

et al. 2014

The Journal of Chemical Physics

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Fluctuations within the ligand shell of a nanoparticle give rise to a significant degree of anisotropy in effective pair interactions for low grafting densities [B. Bozorgui, D. Meng, S. K. Kumar, C. Chakravarty, and A. Cacciuto, Nano Lett. 13, 2732 (2013)]. Here, we examine the corresponding fluctuation-driven anisotropy for gold nanocrystals densely passivated with short ligands. In particular, we consider gold nanocrystals capped by alkylthiols, both in vacuum and in ethane solvent at high density. As in the preceding study, we show that the anisotropy in the nanoparticle pair potential can be quantified by an angle-dependent correction term to the isotropic potential of mean force (PMF). We find that the anisotropy of the ligand shells is distance dependent, and strongly influenced by ligand interdigitation effects as well as expulsion of ligand chains from the interparticle region at short distances. Such fluctuation-driven anisotropy can be significant for alkylthiol-coated gold nanoparticles, specially for longer chain lengths, under good solvent conditions. The consequences of such anisotropy for self-assembly, specially as a function of grafting density, solvent quality and at interfaces, should provide some interesting insights in future work. Our results clearly show that an isotropic two-body PMF cannot adequately describe the thermodynamics and assembly behavior of nanoparticles in this dense grafting regime and inclusion of anisotropic effects, as well as possibly many-body interactions, is necessary. Extensions of this approach to other passivated nanoparticle systems and implications for self-assembly are considered.

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Switching Between Crystallization and Amorphous Agglomeration of Alkyl Thiol-Coated Gold Nanoparticles

Cited by 42 publications

References 25 publications

Ligand-Mediated Interactions between Nanoscale Surfaces Depend Sensitively and Nonlinearly on Temperature, Facet Dimensions, and Ligand Coverage

Ligand-Mediated Interactions between Nanoscale Surfaces Depend Sensitively and Nonlinearly on Temperature, Facet Dimensions, and Ligand Coverage

Nonadditivity of nanoparticle interactions

Fluctuation-driven anisotropy in effective pair interactions between nanoparticles: Thiolated gold nanoparticles in ethane

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