Salt-mediated kinetics of the self-assembly of gold nanorods end-tethered with polymer ligands

Abstract

Studies on the self-assembly of metal nanoparticles (NPs) in the presence of ions are motivated by the biosensing applications of NP clusters and the capability to control the morphology of clusters of oppositely charged NPs. The effect of ions has been explored for the self-assembly of metal NPs capped solely with ionic ligands, whereas, in general, the surface of NPs can be coated with a mixture of ligands interacting with each other by non-electrostatic forces. In the present work, we examined the kinetics of self-assembly of gold nanorods capped with a mixture of low-molecular weight ionic molecules and nonpolar polymer ligands. We show that in contrast with earlier reports on the effect of electrolytes on NP self-assembly, the driving force for the accelerated self-assembly of nanorods is the reduction in polymer solubility in the presence of ions, rather than the screening of the electric double layer of the charged ligands. The reported results are important for NP self-assembly occurring in mixed solvents, in which attraction forces between nonpolar ligands are governed by the balance between solvent-solvent and solvent-salt interactions. Furthermore, the addition of salts can be used to increase the rate of nanorod self-assembly, which, otherwise, is an intrinsically slow process.

Colloidal molecules and patchy particles: complementary concepts, synthesis and self-assembly

“…143 Lastly, the authors reported that in the presence of salts, the major driving force for selfassembly is a decrease in solubility of the PS ligands rather than a screening of the electrostatic repulsion. 144 Photo-crosslinking of poly(styrene-co-isoprene) end-functionalized gold nanorods was also demonstrated as a useful means to covalently fix the bond angles in the chains. 145 This journal is © The Royal Society of Chemistry 20xx d) random copolymers and e) block-copolymers from nanorods of two different lengths, and f) random copolymers from gold and palladium nanorods.…”

Self-assembly of colloidal polymers from two-patch silica nanoparticles

“…Nano Res. Kumacheva and co-workers enhanced the patchiness of the CTAB-coated gold nanorods by the functionalization of their tips with thiol-terminated polystyrene (PS) chains, which enabled the formation of linear and cyclic colloidal polymers when dispersed in binary solvent mixtures [22][23][24][25][26][27]. The driving force of the polymerization of the tip-functionalized nanorods derived from the solvation free energy reduction between the isolated particles and their assembly.…”

Structural Transitions in Nanoparticle Assemblies Governed by Competing Nanoscale Forces

“…To validate the argument about competing E h and E el , we conducted NP self-assembly in the DMF/water mixture in the presence of NaCl. The addition of NaCl to the DMF/water mixture reduced the quality of solvent for the PS ligands 23 and suppressed the electric double layer interactions of the NPs, 24 thus favoring “non-directional” hydrophobic forces and the formation of globules. This trend is shown in Table 1: with increasing content of NaCl in the DMF/water mixture, C → G transitions took place, with an intermediate regime, in which both species were present.…”