Regulation of Interparticle Forces Reveals Controlled Aggregation in Charged Nanoparticles

Abstract

The ability to control interparticle forces not only improves the existing nanoparticle (NP) functionalities but paves the way for newer properties as well. A proof of concept in this direction is presented here, wherein the regulation of interparticle forcesrevealing controlled aggre-gationhas been successfully translated into the trapping and scavenging of toxic ions. A perfect balance between the attractive and repulsive forces is achieved by tuning the [+] and [−] ligands on the surface of heterogeneously charged metal NPs. The NP−ion aggregates are stable for ∼2 days, with a visible color change (Δλ max = 12−15 nm), which makes them available for scavenging from the site of action. The incorporation of "potent" forces like repulsions, rather than a mere dilution of attractive forces, is necessary to ensure the formation of controlled aggregates. The net surface charge of NPs is conveniently modified to trap ions irrespective of their charge and binding strength. More importantly, the regulation of interparticle forces imparts a new function of selectivity toward trapping of toxic ions in a carboxylate functionalized NP system. Thus, the present work introduces a conceptually unprecedented approach to impart long-term stability (∼2 days) to NP−ion aggregates by controlling the interparticle forces.

Stimuli-responsive self-assembly of nanoparticles

“…To tackle this issue, Pillai et al systematically studied how the colloidal stability of the NPs is affected by the incorporation of different amounts of thiols terminated with positively charged groups (NMe 3 + ) within monolayers of COO À -terminated ligands. 34 Upon addition of Pb 2+ , NPs co-functionalized with 80% of a COO À -and 20% of an NMe 3 + -terminated thiol formed small aggregates of B50 nm in size (demonstrated by dynamic light scattering (DLS), atomic force microscopy, and TEM), which exhibited maximum absorbance at B528 nm. Importantly, including the positively charged component within the protective coating was also essential for reversing the self-assembly.…”

“…Within aggregates composed of NPs lacking the positively charged groups, however, Pb 2+ ions were bound too tightly and could not be removed using NaOH. 34 Self-assembly can be highly directional for NPs whose surfaces are functionalized with patches of metal-ion-responsive ligands. Such site-selective functionalization can be readily achieved in anisotropic NPs; for example, the side faces of CTAB-coated Au nanorods are protected more strongly than their tips, where the ligand exchange reaction occurs preferentially.…”

Solvation of quantum dots in 1-alkyl-1-methylpyrrolidinium ionic liquids: toward stably luminescent composites

“…Surface-capping ligands on NPs further enhance the colloidal stability in ILs especially against temperature and concentration-induced agglomeration [1]. Charged ligands are available to control the colloidal stability of NPs in water in terms of electrostatic stabilization [20][21][22][23]. Imidazolium-functionalized surface ligands are often employed to improve the affinity of NP surface to imidazolium-based ILs [24,25].…”

A Paper‐Based Platform for Long‐Term Deposition of Nanoparticles with Exceptional Redispersibility, Stability, and Functionality

“…However, lyophilization still requires a time‐consuming (24–72 h) multistep procedure, a sample‐dependent preparation process, and costly and specialized equipment with a sublimation controlled vacuum pump. Besides, as both the salt and NPs become considerably concentrated during the lyophilization process, significant charge screening and interparticle forces occurring between NPs cause adverse effects on their redispersibility and stability . Thus, a simple strategy that allows long‐term storage of NPs with high stability, redispersibility, and functionality is highly demanded.…”