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2009
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Nguyen TD and Glotzer SC
Switchable helical structures formed by the hierarchical self-assembly of laterally tethered nanorods
Small 5(18), 2092-2098
[x]
View Abstract
The formation of helical scrolls formed by self-assembly of tethered
nanorod amphiphiles and their molecular analogs are investigated. A model
bilayer sheet assembled by laterally tethered nanorods is simulated and
shown that it can fold into distinct helical morphologies under different
solvent conditions. The helices can reversibly transform from one
morphology to another by dynamically changing the solvent condition. This
model serves both to inspire the fabrication of laterally tethered nanorods
for assembling helices at nanometer scales and as a proof-of-concept for
engineering switchable nanomaterials via hierarchical self-assembly.
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Singh C, Jackson AM, Stellacci F, Glotzer SC
Exploiting Substrate Stress To Modify Nanoscale SAM Patterns
Journal of the American Chemical Society
[x]
View Abstract
Self-assembled monolayers (SAMs) have many applications
largely because they can be easily used to engineer surface
properties. Mixed SAMs are particularly attractive because their
properties can be tailored through small changes in composition
and structure. However, there is still incomplete understanding
of how to control structure in mixed SAMs. There is evidence
that substrate stress can affect adsorption of molecules on
surfaces. Recent theoretical studies have further shown that
phase-separated patterns formed on unstressed substrates differ
from those formed on substrates that are stressed prior to
adsorption. Here we demonstrate that stress applied postadsorption
affects diffusion of adsorbed molecules on the surface
and can thus be used to modify surface patterns formed by phase
separation in adsorbed molecular mixtures. We also show how
stress can be used to progress nonequilibrium, kinetically arrested
patterns formed on flat substrates toward equilibrium.
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Kuna JJ, Voïtchovsky K, Singh C, Jiang H, Mwenifumbo S, Ghorai PK, Stevens MM, Glotzer SC and Stellacci F
The effect of nanometre-scale structure on interfacial energy
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View Abstract
Natural surfaces are often structured with nanometre-scale domains, yet a framework providing a quantitative understanding of how nanostructure affects interfacial energy, gamma_SL, is lacking. Conventional continuum thermodynamics treats gamma_SL solely as a function of average composition, ignoring structure. Here we show that, when a surface has domains commensurate in size with solvent molecules, gamma_SL is determined not only by its average composition but also by a structural component that
causes gamma_SL to deviate from the continuum prediction by a substantial amount, as much as 20 n our system. By contrasting surfaces coated with either molecular- (<2 nm) or larger-scale domains (>5 nm), we find that whereas the latter surfaces have the expected linear dependence of
SL on surface composition, the former show a markedly different non-monotonic
trend. Molecular dynamics simulations show how the organization of the solvent molecules at the interface is controlled by the nanostructured surface, which in turn appreciably modifies gamma_SL.
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Phillips CL and Crozier, PS
An energy-conserving two-temperature model of radiation damage in single-component and binary Lennard-Jones crystals
Journal of Chemical Physics
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View Abstract
Two-temperature models are used to represent the interaction between atoms and free electrons during thermal transients such as radiation damage, laser heating, and cascade simulations. In this paper, we introduce an energy-conserving version of an inhomogeneous finite reservoir two-temperature model using a Langevin thermostat to communicate energy between the electronic and atomic subsystems. This energy-conserving modification allows the inhomogeneous two-temperature model to be used for longer and larger simulations and simulations of small energy phenomena, without introducing nonphysical energy fluctuations that may affect simulation results.
We test this model on the annealing of Frenkel defects. We find that Frenkel defect annealing is largely indifferent to the electronic subsystem, unless the electronic subsystem is very tightly coupled to the atomic subsystem. We also consider radiation damage due to local deposition of heat in two idealized systems. We first consider radiation damage in a large face-centered-cubic Lennard-Jones (LJ) single-component crystal that readily recrystallizes. Second, we consider radiation damage in a large binary glass-forming LJ crystal that retains permanent damage. We find that the electronic subsystem parameters can influence the way heat is transported through the system and have a significant impact on the number of defects after the heat deposition event. We also find that the two idealized systems have different responses to the electronic subsystem. The single-component LJ system anneals most rapidly with an intermediate electron-ion coupling and a high electronic thermal conductivity. If sufficiently damaged, the binary glass-forming LJ system retains the least permanent damage with both a high electron-ion coupling and a high electronic thermal conductivity. In general, we find that the presence of an electronic gas can affect short and
long term material annealing.
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Jankowski, E and Glotzer SC
A comparison of new methods for generating energy-minimizing configurations of patchy particles
Journal of Chemical Physics 131, 104104
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View Abstract
Increasingly complex particles are pushing the limits of traditional simulation techniques used to
study self-assembly. In this work, we test the use of a learning-augmented Monte Carlo method for
predicting low energy configurations of patchy particles shaped like “Tetris®” pieces. We extend this
method to compare it against Monte Carlo simulations with cluster moves and introduce a new
algorithm—bottom-up building block assembly—for quickly generating ordered configurations of
particles with a hierarchy of interaction energies.