Nanoparticle Interactions Guided by Shape‐Dependent Hydrophobic Forces

Abstract

Self-assembly of solvated nanoparticles (NPs) is governed by numerous competing interactions. However, relatively little is known about the time-dependent mechanisms through which these interactions enable and guide the nanoparticle self-assembly process. Here, using in situ transmission electron microscopy imaging combined with atomistic modeling, it is shown that the forces governing the self-assembly of hydrophobic nanoparticles change with the nanoparticle shapes. By comparing how gold nanospheres, nanocubes, nanorods, and nanobipyramids assemble, it is shown that the strength of the hydrophobic interactions depends on the overlap of the hydrophobic regions of the interacting nanoparticle surfaces determined by the nanoparticle shapes. Specifically, this study reveals that, in contrast to spherical nanoparticles, where van der Waals forces play an important role, hydrophobic interactions can be more relevant for nanocubes with flat side faces, where an oriented attachment between the nanocubes is promoted by these interactions. The attachment of nanocubes is observed to proceed in two distinct pathways: nanocubes either: (i) prealign their faces before the attachment, or (ii) first connect through a misaligned (edge-to-edge) attachment, followed by a postattachment alignment of their faces. These results have important implications for understanding the interaction dynamics of NPs and provide the framework for the design of future self-assembled nanomaterials.

In Situ Tracking of Colloidally Stable and Ordered Assemblies of Gold Nanorods

“…Recent reports have focused on in situ imaging of the self-assembly of anisotropic nanoparticles, providing insight into the behavior of nanocubes, 17 branched nanooctapods, 23 and nanoprisms. 24 , 25 In the case of NRs two reports on in situ imaging should be highlighted.…”

Macroscopic Orientational Gold Nanorods Monolayer Film with Excellent Photothermal Anticounterfeiting Performance

“…[ 37 ] It is noteworthy that Au NRs with aspect ratios higher than 3.5 were probably formed spontaneously into the orientational assemblies under the assistance of CTAB. [ 38 − 40 ] There are several differences between our approach and the previous work. The previous assembly based on CTAB interaction is conducted on solid substrate and the assembly area is limited.…”

“…[ 52,53 ] However, many investigations have shown that CTAB molecules presented promoting effects with concentrating Au NRs solution via strong van der Waals (vdW) forces. [ 38 − 40 ] Therefore, the Au NRs forming multiple assembling morphologies were expected from the interaction between CTAB molecules (Figure 2a – c). As shown in Figure S3, Supporting Information, four assembly modes were revealed according to the interaction manner (sharing a common layer of counterions or interdigitating of CTAB tails from neighboring NPs) of CTAB.…”

Interactions of sub-five-nanometer diameter colloidal palladium nanoparticles in solution investigated via liquid cell transmission electron microscopy

“…To date, remarkable progress has been achieved on revealing the mechanisms of colloidal NP interactions via different characterization tools, such as small-angle X-ray scattering, 4 zeta potential measurement, 5,10 UV-Vis spectra, 1, 11 and in situ streaming potential measurements. [12][13][14] Recently, liquid cell transmission electron microscopy (LCTEM), as an emerging technique with the capability of imaging at high spatialtemporal resolution, 15,16 has been demonstrated as an effective and feasible platform for investigating the growth, 2,3,17 aggregation, [18][19][20][21][22] etching, [23][24][25] self-assembly, [26][27][28][29][30][31] electrochemical reaction, 32 and bio-application 33 of nanosized objects in aqueous solution.…”