Entropy-Mediated Patterning of Surfactant-Coated Nanoparticles and Surfaces

Abstract

We perform atomistic and mesoscale simulations to explain the origin of experimentally observed stripelike patterns formed by immiscible ligands coadsorbed on the surfaces of gold and silver nanoparticles. We show that when the conformational entropy gained via this morphology is sufficient, microphase-separated stripelike patterns form. When the entropic gain is not sufficient, we instead predict bulk phase-separated Janus particles. We also show corroborating experimental results that confirm our simulational predictions that stripes form on flat surfaces as well as on curved nanoparticle surfaces.

The role of nanostructure in the wetting behavior of mixed-monolayer-protected metal nanoparticles

“…It is known that most mixtures of thiolated molecules when coassembled on flat gold surfaces phase-separate into randomly sized and arranged domains (11,12). Recently (13)(14)(15)(16)(17)(18)(19), using scanning tunneling microscopy (STM) and infrared spectroscopy, we found that when gold nanoparticles are coated with these same types of binary mixtures of molecules, phase separation occurs in a more ordered fashion, leading to the formation of ribbonlike domains of alternating composition with an unprecedented small average domain width of ϳ5 Å (see cartoon in Fig. 1).…”

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.…”

Contact angle and adsorption energies of nanoparticles at the air–liquid interface determined by neutron reflectivity and molecular dynamics

“…However, the NR profile can detect the presence of domains like those formed in amphiphilic Janus NPs, where each domain is preferentially immersed in one of the two media and the domain boundary is parallel to the interface. This Janus morphology can be obtained during the synthesis and it is driven by the interplay of enthalpic and entropic effects 39 as well as kinetic effects. 45,46 To test the possible existence of Janus NPs in our monolayers, we modeled the NPs with Janus nanodomain structure (see ESI †) and fitted the experimental data to this model.…”

“…[36][37][38] Among these arrangements, Janus (two different sides), narrow nanodomains (stripes) and uniformly mixed morphologies have been reported in experimental and theoretical papers. [39][40][41] The size of NPs, chemical nature of the ligands and their arrangement at the surface affect their interaction with interfaces and therefore their use in different applications.…”