24,379 research outputs found
Molecular Simulation of MoS2 Exfoliation.
A wide variety of two-dimensional layered materials are synthesized by liquid-phase exfoliation. Here we examine exfoliation of MoS2 into nanosheets in a mixture of water and isopropanol (IPA) containing cavitation bubbles. Using force fields optimized with experimental data on interfacial energies between MoS2 and the solvent, multimillion-atom molecular dynamics simulations are performed in conjunction with experiments to examine shock-induced collapse of cavitation bubbles and the resulting exfoliation of MoS2. The collapse of cavitation bubbles generates high-speed nanojets and shock waves in the solvent. Large shear stresses due to the nanojet impact on MoS2 surfaces initiate exfoliation, and shock waves reflected from MoS2 surfaces enhance exfoliation. Structural correlations in the solvent indicate that shock induces an ice VII like motif in the first solvation shell of water
Molecular simulation of liquid crystals
This article reviews recent progress in the computer simulation of liquid crystals at the molecular level. It covers the use of simple rigid-body models of the constituent molecules, and more detailed modelling via atomistic force fields. Bulk mesophases, inhomogeneous systems, and interfaces, are discussed. Recent progress in calculating elastic properties and dynamics is summarized. As well as presenting an overview, some specific topics of recent interest are highlighted: the biaxial nematic phase, chiral phases, ionic liquid crystals, and charge-transfer systems
Molecular simulation of thin liquid films : thermal fluctuations and instability
The instability of a thin liquid film on a solid surface is studied both by molecular dynamics simulations (MD) and a stochastic thin-film equation (STF), which models thermal fluctuations with white noise. A linear stability analysis of the STF allows us to derive a power spectrum for the surface fluctuations, which is quantitatively validated against the spectrum observed in MD. Thermal fluctuations are shown to be critical to the dynamics of nanoscale films. Compared to the classical instability mechanism, which is driven by disjoining pressure, fluctuations (a) can massively amplify the instability, (b) cause the fluctuation wavelength that is dominant to evolve in time (a single fastest-growing mode does not exist), and (c) decrease the critical wavelength so that classically stable films can be ruptured
Molecular simulation analysis of structural variations in lipoplexes
We use a coarse-grained molecular model to study the self-assembly process of
complexes of cationic and neutral lipids with DNA molecules ("lipoplexes") - a
promising nonviral carrier of DNA for gene therapy. We identify the resulting
structures through direct visualization of the molecular arrangements and
through calculations of the corresponding scattering plots. The latter approach
provides a means for comparison with published data from X-ray scattering
experiments. Consistent with experimental results, we find that upon increasing
the stiffness of the lipid material, the system tends to form lamellar
structures. Two characteristic distances can be extracted from the scattering
plots of lamellar complexes - the lamellar (interlayer) spacing and the
DNA-spacing within each layer. We find a remarkable agreement between the
computed values of these two quantities and the experimental data [J. O.
R\"{a}dler, I. Koltover, T. Salditt and C. R. Safinya, Science Vol. 275, 810
(1997)] over the entire range of mole fractions of charged lipids (CLs) studied
experimentally. A visual inspection of the simulated systems reveals that, for
very high fractions of CLs, disordered structures consisting of DNA molecules
bound to small membrane fragments are spontaneously formed. The diffraction
plots of these non-lamellar disordered complexes appear very similar to that of
the lamellar structure, which makes the interpretation of the X-ray data
ambiguous. The loss of lamellar order may be the origin of the observed
increase in the efficiency of lipoplexes as gene delivery vectors at high
charge densities.Comment: Accepted for publication in "Soft Matter
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