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When a nano-drop comprising a single spherical central ion and dielectric solvent is charged above a well-defined threshold, it acquires a stable star morphology. In contrast, conducting droplets, will undergo fission. Here we report combined atomistic molecular dynamics and continuum modelling study of star formation of droplets that contain a highly charged ion. We assume that in the continuum model the dielectric response is linear. In this linear continuum model, which is an extension of Rayleigh model, the energy of the drop is comprised of terms analogous to those in Rayleigh model, which are surface energy and electrostatic energy of dielectric droplet charged by a central point charge. We present the stability analysis of the continuum model to determine the threshold of instability. Indeed we find that the model accounts well for the onset of the instabilities. Molecular dynamics show that the number of points of the star-shaped nano-drops depends only on the surface tension, dielectric constant and size of the droplet, and on the magnitude of the charge of the central ion, but not on its sign. Intuitively, it is expected that when a spherical dielectric drop becomes unstable it would transform into a non-spherical finite shape of the same volume as the initial spherical shape with the point charge located in the drop interior. To test whether the extended Rayleigh model can account for the observed droplet shapes, we performed numerical simulations of the linear continuum model. Contrary to the expectations, the simulations of the extended Rayleigh model does not reproduce the stable star shapes found in the atomistic simulations, not even when we account for the bending rigidity and spontaneous curvature of the surface. We argue that the assumption that the dielectric response is linear breaks down if the droplet surface approaches the central macro-ion, where the electric field strength is such that dielectric saturation sets in. We envisage that for certain solvents, these stars could be made permanent by cross-linking, opening the way to the production of a novel class of highly-non-convex colloids.

We report the first detailed molecular dynamics study of two carbon nanoparticles (nanotubes or fullerenes) embedded in a droplet of chloroform. The carbon nanoparticles are negatively charged and are accompanied by the positive counterions of sodium. On the one hand, this setup is inspired by the carbon nanoparticle salts—“nanotubides” and “fullerides”—proposed recently as a convenient way to address the difficult problem of the dispersion of carbon nanoparticulates in the organic solvents. On the other hand, the electrospray of carbon nanoparticle suspensions has been shown to be a promising technique for the production of thin nanoparticle coatings. We explore the combination of these two approaches by using molecular simulations. We find that depending on the overall electrostatic charge balance the two nanoparticles can exist in the droplet either in the “salted-out” bound state or in a “solvent-separated” state. The latter opens up the possibility for the efficient dispersion of the nanoparticles in...

An ultrathin water film confined between two substrates in moving contact is studied using Langevin molecular dynamics with a coordinate- and velocity-dependent damping coefficient. The water molecules are modeled with the Central-Force model that allows for the dissociation of water molecules into H+ and OH–. Two different friction scenarios are found depending on the applied pressure and the strength of the interaction of water with substrates. Under low loads, the water molecules stay intact during the frictional sliding. However, when the applied pressure increases past a value of ∼20 GPa, the water molecules begin to dissociate and recombine immediately in the course of sliding, which results in a large increase of friction. The rate of such dissociation is found to be roughly proportional to the speed of driving. The relation of the observed phenomena to the “superionic” and “ionic fluid” states of water and its relevance in practical friction situations is discussed.

Based on computer simulation, it is proposed that so-called RNA nanotubes, which are sequences of bonded RNA nanorings, be used for optical applications in manufacturing metamaterials. A recently developed model of coarse-grained RNA is used that allows the study of key properties of RNA nanotubes. The Langevin method is used to discover the basic thermodynamic and mechanical properties of nanotubes and their response to an external field.

We consider the propagation of 2D solitary electromagnetic waves and their scattering on a lattice of metallic inhomogeneities in the system of carbon nanotubes (CNTs). The electromagnetic field is considered on the basis of Maxwell equations, and the electronic system of carbon nanotubes is treated by the Boltzmann equation in relaxation time approximation. We numerically analyze the derived effective equation and reveal an increase of spectral composition of the last electromagnetic wave. Some possible practical applications of the discovered effect are discussed.

We consider Maxwell equations for an electromagnetic field propagating in carbon nanotubes (CNTs) placed on a dispersive nonmagnetic dielectric medium. We obtain the effective equation analogous to the classical sine-Gordon equation. Then it has been analyzed numerically. We have revealed the dependence of the pulse on the type of CNT and on the initial pulse amplitude, as well as on the medium dispersion constants.

Starting with the Dirac equation in a curved space–time, applied for the description of the long-wave electrons in curved graphene nanoribbons, we calculated the electronic spectrum and the density of states. Based on the derived density of states we were able to compute the I V -characteristics of a nanoribbon–metal tunnel junction. The dependence on the geometric characteristics of a nanoribbon is revealed.

A melting phase transition in a thin lubricant film confined between two substrates in moving contact is considered. General theoretical arguments are usually used to prove that ordinary bulk melting is always a first-order phase transition. However, this is not the case for systems with static and dynamic asymmetries. It is shown theoretically that a given tribological system can exhibit a novel two-stage continuous second-order transition, which is confirmed by a Langevin molecular dynamics study.

It is of great value to develop a simple, controllable, and scalable method of making superamphiphobic surfaces. Here we present a facile one-step photolithographic method to engineer superamphiphobic surfaces consisting of photoresist micropillars decorated with nanoparticles of the same photoresist. The surface or coating is optically transparent and versatile, and can be fabricated on a broad range of substrates including stretchable elastomers. During the development of the micropillar array, photoresist nanoparticles are spontaneously grown on the micropillars by a well-controlled emulsification process of the un-cross-linked residual photoresist. This creates a hierarchical structure with a re-entrant and convex morphology which is the key for superoleophobicity. The chemical bonding between the nanoparticles and the micropillars is strong producing a robust and durable coating. This facile method is scalable and industry-applicable for a variety of applications such as self-cleaning, antifouling, and deicing/antifrosting.

An ultrathin water film confined between two substrates in moving contact is studied using Langevin molecular dynamics with coordinate- and velocity-dependent damping coefficient. The correlations between the structure of the water lubricant film and its frictional properties are found in a wide range of applied loads and for various strengths of interactions between water and surfaces. A self-organization of the film into a low-friction state under driving is observed to occur. Surprisingly, it is found that the “hydrophilic” surfaces exhibit a lower friction than the “hydrophobic” ones. The viscosity of the confined water estimated from the simulations is in a good agreement with the experimental value.

We study the spatial distribution of conformational isomers surrounding a central macroion in a charged droplet with linear dimensions in the nanometer range. Dimethyl carbonate and formic acid are selected as typical solvents that undergo isomerization and a charged buckyball (C60) is selected as a representative example of a macroion. The study is performed by atomistic molecular dynamics simulations. We find that when the charge of the buckyball is above a threshold value, it induces the formation of concentric shells of different conformational isomers surrounding the macroion. The presence of layers with different dielectric properties necessitates the use of different state equations for the solvent polarization in each layer. We find that at a high charge state of the buckyball, the nearest layer to the macroion comprises the conformers with the highest dipole moment. The interface of the outer layers of conformers is characterized by “ray”-forming structures of the higher dielectric constant isome...

Thin polymeric films made with various elastomers, like polyisoprene, and elastomer composites were prepared for char- acterization of cross-linking depth in this study. Various cross-linking methods have been applied to get mechanically stronger, more thermally stable and chemically resistant polymer coatings. However, there is no existing approach that could effectively characterize the degree or depth of cross-linking for thin polymer films. The objective of this work is to use atomic force microscopy to character- ize cross-linking depth in a precise way. Hyperthermal hydrogen bombardment-induced cross-linking was employed as a cross-linking method and the depth of cross-linking was estimated via local change of the elastic modulus along the sample cross-section with pre- cise force measurement and high spatial resolution. It is found that the cross-linking depth is closely related to the chemical composi- tion of thin films. Understanding the depth of cross-linking is vital for a broad range of applications. It is believed that the developed technique is also applicable for studying other cross-linkable materials. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41493.

A facile method for cross-linking organic molecules has been developed by computational modeling, instrumentation design, and experimental research. Briefly, organic molecules are hit by H2 with controllable kinetic energy in our novel apparatus where a high flux of hyperthermal H2 is generated. When a C-H bond of the organic molecule is hit by H2 at about 20 eV, efficient kinematic energy-transfer in the H2→H collision facilitates the C-H dissociation with nearly 100% reaction probability. When H2 hits other atoms which are by nature much heavier than H2, mass disparity bars effective energy transfer and this both blocks undesirable bond dissociation and reduces unnecessary energy wastage. The recombination of the carbon radicals generated by the C-H cleavage efficiently completes the production of C-C cross-links at room temperature with no additional energy/chemicals requirements. In addition to these green chemistry merits, this new method is better than other cross-linking techniques which rely on prerequisite reactions to add cross-linkers to the organic molecules or additional reactants and additives. These promising features are validated by several cross-linking trials which demonstrate desirable mechanical, electrical, chemical, and biochemical changes while inducing no undesirable damage of chemical functionalities in the original molecules. © 2014 The Royal Society of Chemistry.

A series of coarse-grained models have been developed for study of the molecular dynamics of RNA nanostructures. The models in the series have one to three beads per nucleotide and include different amounts of detailed structural information. Such a treatment allows us to reach, for systems of thousands of nucleotides, a time scale of microseconds (i.e. by three orders of magnitude longer than in full atomistic modeling) and thus to enable simulations of large RNA polymers in the context of bionanotechnology. We find that the three-beads-per-nucleotide models, described by a set of just a few universal parameters, are able to describe different RNA conformations and are comparable in structural precision to the models where detailed values of the backbone P-C4′ dihedrals taken from a reference structure are included. These findings are discussed in the context of RNA conformation classes. © 2010 IOP Publishing Ltd.

A thin lubricant film confined between two substrates in moving contact is studied using Langevin molecular dynamics with the coordinate- and velocity-dependent damping coefficient. It is shown that an optimal choice of the interaction within the lubricant can lead to minimal kinetic friction as well as to low critical velocity of the stick-slip to smooth-sliding transition. The strength of this interaction should be high enough (relative to the strength of the interaction of lubricant atoms with the substrates) so that the lubricant remains in a solid state during sliding. At the same time, the strength of the interaction should not be too high, in order to allow annealing of defects in the lubricant at slips.

The exotic quantum phenomenon of Bose–Einstein condensation (BEC) is the key ingredient in a new type of laser that emits atoms rather than photons, and that promises to revolutionize atom optics. In this paper, we consider the possibility of stable angular momentum transfer by an atom laser beam which should be more useful in various applications than a circularly polarized photon laser. The most promising way to assign the initial angular momentum is the outcoupling from the BEC cloud in a vortex state. However, the question of the vortex stability (metastability) arises as well as stability of the beam angular momentum. Here we propose a method for the solution of this problem by developing a quasi-hydrodynamic approach to the condensate with account of its interaction with the non-condensed atoms. Using the concept of local hydrodynamical invariants, we further derive the necessary conditions for the beam, such that the initial angular momentum is transferred conservatively. Both continuous and pulsed schemes are considered.

We study mechanical and thermodynamic properties of RNA nanostructures focusing on a hexagonal nanoring discussed in Yingling and Shapiro (2007 Nano Lett. 7 2328). We are concerned with the following main issues: (i) the stability of the nanoring versus temperature; (ii) the effect of the environment (solvent, counterions) on its stability; (iii) conformations and dynamics under external force. The process of evaporation of the ions from the ring upon temperature drop has been found, demonstrating a surprising feature-the uptake of ions by the nanoring increases with the temperature. The connection of this behavior to the dielectric constant of water, hydration and structural changes in the nanoring is discussed. Several properties of the nanoring, such as elastic and transport coefficients, have been determined. A measure of the tensile elasticity of the ring against its uniform 2D in-plane compression has been given, as K(eff)or = 0.01 GPa, which is a much lower value compared to typical values found for soft matter other than RNA.