A Thermodynamics Model for the Emergence of a Stripe‐like Binary SAM on a Nanoparticle Surface

Abstract

It has been under debate if a self-assembled monolayer (SAM) with two immiscible ligands of different chain lengths and/or bulkiness can form a stripe-like pattern on a nanoparticle (NP) surface. The entropic gain upon such pattern formation due to difference in chain lengths and/or bulkiness has been proposed as the driving force in literature. Using atomistic discrete molecular dynamics simulations we show that stripe-like pattern could indeed emerge, but only for a subset of binary SAM systems. In addition to entropic contributions, the formation of a striped pattern also strongly depends upon inter-ligand interactions governed by the physicochemical properties of the ligand constituents. Due to the interplay between entropy and enthalpy, we can categorize a binary SAM system into three different types depending on whether and under what condition a striped pattern can emerge. We hope our results help clarify the ongoing debate and our proposed principle can aid in the engineering of novel binary SAMs on a NP surface.

Nanophase Segregation of Self-Assembled Monolayers on Gold Nanoparticles

“…23 Thus, computational approaches may help identifying driving forces to guide the design of new dissymetric, Janus or patchy nanoparticles by the rational choice of reagents and synthesis conditions. Coarse-grain molecular dynamics (MD), [24][25][26][27] Atomistic MD, 28 and Monte Carlo simulations, 28 have identified conformational entropic effects as the driving force for nanophase separation in binary thiol SAMs on gold nanoparticles, provided that the two kinds of molecules are not miscible and have sufficiently different chain lengths. 24,[27][28] Similar conclusions were reached for ternary and quaternary thiol SAMs.…”

“…Coarse-grain molecular dynamics (MD), [24][25][26][27] Atomistic MD, 28 and Monte Carlo simulations, 28 have identified conformational entropic effects as the driving force for nanophase separation in binary thiol SAMs on gold nanoparticles, provided that the two kinds of molecules are not miscible and have sufficiently different chain lengths. 24,[27][28] Similar conclusions were reached for ternary and quaternary thiol SAMs. [25][26]29 However, the role of specific inter-chain interactions on phase segregation has been mostly eluded in simulations, except in very recent reports based on discrete MD simulations, where tail-tail repulsive interactions have been suggested to contribute to nanophase segregations for some specific ligand types.…”

“…[25][26]29 However, the role of specific inter-chain interactions on phase segregation has been mostly eluded in simulations, except in very recent reports based on discrete MD simulations, where tail-tail repulsive interactions have been suggested to contribute to nanophase segregations for some specific ligand types. 27 Besides, modeling could also address mechanisms of phase segregation at the molecule-scale, such as surface diffusion or desorption-adsorption processes, although studies in this direction have been only scarcely reported. 30 The aim of this work is the development of rational and reliable models to study the behaviors and properties of mixed organic SAMs at the surface of gold planar surfaces and nanoparticles exhibiting full (Janus) or partial (patchy) phase segregation.…”

Quantified Binding Scale of Competing Ligands at the Surface of Gold Nanoparticles: The Role of Entropy and Intermolecular Forces

“…First, quantified partition could be used to predict the composition of the mixed SAM for a given ligand ratio in the initial solution, and even to select the right initial ratio to reach a targeted surface composition. Second, and more fundamentally, quantifying the partition for a series of well‐chosen ligands should provide new insights into the role of the chain length and functionality, and of the end‐group on ligand exchange and the stability of mixed ligand shells. In brief, such quantified partitions may contribute to decipher the impact of intermolecular forces and entropic effects on the stability of the ligand shells and their role as driving forces for ligand exchange—a topical issue for the control of nanoparticles properties and self‐assembly …”

Brushed polyethylene glycol and phosphorylcholine for grafting nanoparticles against protein binding

“…2), we included two IONP sizes of 10 nm and 7 nm in diameter in the simulations. We followed a previous computational approach 26 to model the ligand-grafted NPs with a total of 50 ligands per NP, approximating the average number of ligands per NP during experimental synthesis 20 . As a result, the ligand density for the 7 nm IONP approximately doubled that of the 10 nm IONP.…”