Coarse-grained molecular-dynamics simulations of nanoparticle diffusion in polymer nanocomposites

Molecular-dynamics simulations have emerged as an effective tool to characterize polymer systems. Molecular level effects (even on microsecond time scales) are nowadays well reproduced by atomistically detailed models. Beyond this, further insights into the properties of the polymer system at a mesoscopic level can be gained by resorting to simulations based on appropriate coarse-grained models. However, reducing the number of degrees of freedom during the coarse-graining procedure may have a significant impact on atomistic level effects. A common example is the overall enhancement of the diffusive motion of polymer chains in coarse-grained simulations, which arises from the reduced friction of the coarse-grained beads. In the present work we investigate this well-known effect and study how the diffusive properties of the nanoparticle are affected by the coarse-graining procedure. To this end, we apply iterative Boltzmann inversion to develop two coarse-grained models of a nanocomposite based on the thermoplastic polyimide R-BAPB, containing a single fullerene C60 nanoparticle. By changing the size and, correspondingly, the total number of coarse-grained beads in each polymer chain, we can control the effect of chemical detalization on various phenomena. We exploit this idea to study the influence of the degree of detalization of polymer chains on their structural properties as well as on the diffusive properties of the fullerene nanoparticle, whose detalization is kept fixed. Although the structural properties of the coarse-grained systems are in good agreement with those of the fully atomistic system, the nanoparticle diffusion is significantly affected by the local chain structure. In particular, we find that the coarse-graining of the polymer chains on the length scale of the nanoparticle size leads to a full suppression of the subdiffusive regime observed in the fully atomistic system

Magnetic location of a possible earthquake epicentre area: a mathematical model

We study one of the problems of the theory of seismo-electromagnetic methods of earthquake prediction, namely, the physical nature of magnetic location of a future epicentre. According to numerous magneto-telluric soundings and geological theory of ore genesis, high seismicity lithosphere zones typically contain structures with high electric conductivity of the order of 0.01–0.1 S/m. Taking account of this particularity of the seismically active lithosphere zones, we applied the physical theory of magneto-thermo-elasticity and formulated a mathematical model of magnetic location of an area emitting a seismically generated electromagnetic field (an area with repeated emissions is expected to be the epicentre area of a future earthquake). In other words, we explained, on a rational geological, physical, and mathematical basis, why it occurred to be possible that Prof. Kopytenko (IZMIRAN, Russian Academy of Science) and co-authors have localized the future epicentre area as the result of the magnetic field measurements

Computer simulations of the heat-resistant polyimides ULTEM and EXTEM using Gromos53a6 and Amber99 force fields

An atomistic computer simulation was performed for the polyimides ULTEM™ and EXTEM™ via the molecular-dynamics method with the use of Gromos53a6 and Amber99 force fields. For parameterization of electrostatic interactions, the partial atomic charges were calculated through quantum-chemical methods. The temperature dependence of density and the thermal-expansion coefficients for the polyimides were obtained. The calculated density values of the polyimides at room temperature and their coefficients of thermal expansion in the glassy state are in agreement with available experimental data. It is shown that inclusion of electrostatic interactions is necessary for simulation of the thermophysical characteristics of the considered polyimides

Molecular dynamics simulation of poly(3-hexylthiophene) helical structure in vacuo and in amorphous polymer surrounding

The stability of poly(3-hexylthiophene) (P3HT) helical structure has been investigated in vacuo and in amorphous polymer surrounding via molecular dynamics-based simulations at temperatures below and above the P3HT melting point. The results show that the helical chain remains stable at room temperature both in vacuo and in amorphous surrounding, and promptly loses its structure at elevated temperatures. However, the amorphous surrounding inhibits the destruction of the helix at higher temperatures. In addition, it is shown that the electrostatic interactions do not significantly affect the stability of the helical structur

Calorimetry for Lepton Collider Experiments – CALICE results and activities

The CALICE collaboration conducts calorimeter R&D for highly granular calorimeters, mainly for their application in detectors for a future lepton collider at the TeV scale. The activities ranges from generic R&D with small devices up to extensive beam tests with prototypes comprising up to several 100000 calorimeter cells. CALICE has validated the performance of particle flow algorithms with test beam data and delivers the proof of principle that highly granular calorimeters can be built, operated and understood. The successes achieved in the past years allows the step from prototypes to calorimeter systems for particle physics detectors to be addressed

CALICE Report to the DESY Physics Research Committee

We present an overview of the CALICE activities on calorimeter development for a future linear collider. We report on test beam analysis results, the status of prototype development and future plans.We present an overview of the CALICE activities on calorimeter development for a future linear collider. We report on test beam analysis results, the status of prototype development and future plans

Report to the DESY PRC

We present an overview of the CALICE activities on calorimeter development for a future linear collider. We report on test beam analysis results, the status of prototype development and future plans