Investigation of the Crossover From Simple Liquid‐Like to a Polymer‐Like Behavior of Polyisoprene by Means of MD Simulations

The crossover from small‐molecule to polymer behavior in realistic models of PI at temperatures well above the glass transition is investigated by means of MD simulations. The molar masses range from the monomer to = 6 800 g · mol⁻¹ which is far from the critical value for entanglement in PI. It is shown that at this temperature the non‐Gaussian parameter almost vanishes in the Q‐range studied. This implies Gaussian behavior in almost all the Q‐range. From the mean square displacement and the incoherent scattering function behavior a smooth transition from the microscopic regime to the Rouse dynamics is observed. The Rouse behavior is achieved at chain molecular weights of about 1 000 g · mol⁻¹, which corresponds to 14 monomer units.

     

Self-assembled pattern formation of block copolymers on the surface of the sphere using self-consistent field theory

The spherical surface is spatially discretized with triangular lattices to numerically calculate the Laplace-Beltrami operator contained in the self-consistent field theory (SCFT) equations using a finite volume method. Based on this method we have developed a spherical alternating-direction implicit (ADI) scheme for the first time to help extend real-space implementation of SCFT in 2D flat space to the surface of the sphere. By using this method, we simulate the equilibrium microphase separation morphology of block copolymers including AB diblocks, ABC linear triblocks and ABC star triblock copolymers occurred on the spherical surface. In general, two classes of microphase separation morphologies such as striped patterns for compositionally symmetric block copolymers and spotted patterns for asymmetric compositions have been found. In contrast to microphase separation morphology in 2D flat space, the geometrical characteristics of a sphere has a large influence on the self-assembled morphology. For striped patterns, several of spiral-form and ring-form patterns are found by changing the ratio of the radius of a sphere to the averaging width of the stripes. The specific pattern such as the striped and spotted pattern with intrinsic dislocations or defects stems from formed periodic patterns due to microphase separation of block copolymers arranged on the curved surface.     

Classical atomistic simulations of protein adsorption on carbon nanomaterials

Carbon nanomaterials are receiving an increasingly large interest in a variety of fields, including also nanomedicine. In this area, much attention is devoted to investigating and modeling the behavior of these nanomaterials when they interact with biological fluids and with biological macromolecules, in particular proteins and oligopeptides. The interaction with these molecules is in fact crucial to understand and predict the efficacy of nanomaterials as drug carriers or therapeutic agents as well as their potential toxicity when they occupy the active site of a protein or severely affect the secondary and tertiary structure, or even the local dynamics, thus inhibiting their biological function. In this review, therefore, we describe the most recent work carried out in the last few years to model the interaction between carbon nanomaterials, either pristine or functionalized, and proteins or oligopeptides using classical atomistic methods, mainly molecular dynamics simulations. The attention is focused on 0-dimensional fullerenes, mainly C₆₀, on 1-dimensional carbon nanotubes, mostly the single-walled armchair and some chiral ones, and on 2-dimensional graphene and graphyne, the latter containing also sp hybridized atoms in addition to the sp² ones common to the other carbon nanomaterials.     

Investigation of velocity overshoot behavior in p-i-n GaAs semiconductor: The contribution of internal electric field

In this work, we present the investigation of the velocity overshoot behavior in p-i-n GaAs semiconductor based on the ensemble Monte Carlo simulations. Our simulations with high-resolution of time and spatial show that the velocity overshoot effect is originated from internal electric field caused by the difference of carrier density. And this effect is dependent not only on the carrier density but also on temperature. Furthermore, we have observed the velocity relaxation effect which was not recognized before because the external electric field is too high comparing to the internal electric field in semiconductor. We point out that the velocity relaxation can be seen as a damping oscillation in which the damping velocity depends strongly on carrier density but not temperature.     

Investigating the nonequilibrium aspects of long-range Potts model: Refinement of critical temperatures and raw exponents

In this work, we analyze the q-state Potts model with long-range interactions through nonequilibrium scaling relations commonly used when studying short-range systems. We determine the critical temperature via an optimization method for short-time Monte Carlo simulations. The study takes into consideration two different boundary conditions and three different values of range parameters of the couplings. We also present estimates of some critical exponents, named as raw exponents for systems with long-range interactions, which confirm the non-universal character of the model. Finally, we provide some preliminary results addressing the relations between the raw exponents and the exponents obtained for systems with short-range interactions. The results assert that the methods employed in this work are suitable to study the considered model and can easily be adapted to other systems with long-range interactions.     

Time‐dependent simulation of ion stopping: Charge transfer and electronic excitations

The energy loss of charged particles in matter has been studied for many decades, both, analytically and via computer simulations. While the regime of high projectile energies is well understood, low energy stopping in solids is more challenging due to the importance of non‐adiabatic effects and electronic correlations. Here we consider two problems: the charge transfer between substrate and projectile and the role of electronic correlations, specifically formation of doubly occupied lattice sites in the material during the stopping process. The former problem is treated by time‐dependent density functional theory simulations and the latter by non‐equilibrium Green functions.     

Compartmentalized Encapsulation of Two Antibiotics in Porous Nanoparticles: an Efficient Strategy to Treat Intracellular Infections

Combinatorial drug therapies emerge among the most promising strategies to treat complex pathologies such as cancer and severe infections. Biocompatible nanoparticles of mesoporous iron carboxylate metal–organic framework (nanoMOFs) are used here to address the challenging aspects related to the coincorporation of two antibiotics. Amoxicillin and potassium clavulanate, a typical example of drugs used in tandem, are efficiently coincorporated with payloads up to 36 wt%. Due to the occurrence of two distinct pore sizes/apertures within the MOF architecture, each drug is able to infiltrate the porous framework and localize within separate compartments. Molecular simulations predict drug loadings and locations consistent with experimental findings. Drug loaded nanoMOFs that are internalized by Staphylococcus aureus infected macrophages are able to colocalize with the pathogen, which in turn leads to an alleviation of bacterial infection. The data also reveal potential antibacterial properties of nanoMOFs alone as well as their ability to deliver a high payload of drugs to fight intracellular bacteria. These results pave the way toward the design of engineered “all‐in‐one” nanocarriers in which both the loaded drugs and their carrier play a role in fighting intracellular infections.     

A comparative study of aqueous DMSO mixtures by computer simulations and integral equation theories

ABSTRACT

Several computer simulation studies of aqueous-dimethylsulfoxide with different force field models, and conducted by different authors, point out to an anomalous depressing of second and third neighbour correlations of the water–water radial distribution functions. This seemingly universal feature can be interpreted as the formation of linear water clusters. We test here the ability of liquid state integral equation theories to reproduce this feature. It is found that the incorporation of the water bridge diagram function is required to reproduce this feature. These theories are generally unable to properly reproduce atom–atom distribution functions. However, the near-ideal Kirkwood–Buff integrals are relatively well reproduced. We compute the X-ray scattering function and compare with available experimental results, with the particular focus to explain why these data do not reproduce the cluster pre-peak observed in the water–water structure factor.     

Approach to local thermodynamic equilibrium and the evolution to a glassy core following neutron/ion radiation impact

Using molecular dynamics simulations and statistical-mechanical metrics, we make quantitative predictions on the local thermodynamic and dynamic states following an ion or neutron impact in three materials – copper, silicon and solid argon. Through a two-energy distribution, we first capture the non-equilibrium temperature evolution and the approach to the local thermal equilibrium in three generic stages. By examining the time-resolved van Hove self-correlator, we then demonstrate that the impact core of all the three materials shows the dynamic characteristics of a jammed or glassy state. We delineate a dynamic atom-hopping mechanism that attests to a rapid defect recovery stage in copper; silicon, on the contrary, accommodates only small displacements which resist recovery. The dissimilitude between copper with a close-packed structure and silicon with an open network structure is further drawn out through an isoconfigurational analysis of displacements, which shows a compact dendritic-like condensation front for the mobile atoms in copper through atom hopping. In contrast, silicon portrays larger-scale spatial oscillations of dynamically separated regions, which appear to be a precursor to dynamic lattice instability and eventual amorphisation.