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

Scale-dependent miscibility of polylactide and polyhydroxybutyrate:molecular dynamics simulations

\u3cp\u3eMiscibility of polylactide (PLA) and polyhydroxybutyrate (PHB) is studied by the microsecond atomistic molecular dynamics (MD) simulations for the first time. The model and the simulation protocol were confirmed through comparison of the glass transition temperature (T\u3csub\u3eg\u3c/sub\u3e) with experimental data. It was established that PLA and PHB are miscible on the basis of the Flory-Huggins theory. Analysis of the mobilities of PLA and PHB subchains revealed that the blends have two transitions to a glassy state at the length scale of a few Kuhn segments, which is in line with the predictions of the self-concentration model. At the same time at the larger length scale a single transition to a glassy state was observed, suggesting scale dependence of PLA and PHB miscibility. This scale dependence was confirmed through the evaluation of the interchain pair correlation functions.\u3c/p\u3

Scale-dependent miscibility of polylactide and polyhydroxybutyrate:molecular dynamics simulations

\u3cp\u3eMiscibility of polylactide (PLA) and polyhydroxybutyrate (PHB) is studied by the microsecond atomistic molecular dynamics (MD) simulations for the first time. The model and the simulation protocol were confirmed through comparison of the glass transition temperature (T\u3csub\u3eg\u3c/sub\u3e) with experimental data. It was established that PLA and PHB are miscible on the basis of the Flory-Huggins theory. Analysis of the mobilities of PLA and PHB subchains revealed that the blends have two transitions to a glassy state at the length scale of a few Kuhn segments, which is in line with the predictions of the self-concentration model. At the same time at the larger length scale a single transition to a glassy state was observed, suggesting scale dependence of PLA and PHB miscibility. This scale dependence was confirmed through the evaluation of the interchain pair correlation functions.\u3c/p\u3

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

Computer simulation of asphaltenes

The review describes theoretical approaches based on computer simulations at various levels of details (from quantum chemical calculations to atomistic and coarse-grained models) to study asphaltenes and systems containing asphaltenes. The used methods are described, their advantages and disadvantages are discussed in terms of computational costs and time- and spatial-scales available for simulations. The results of studies of the asphaltenes interactions with each other and their aggregation behavior in low-molecular solvents are presented. The most promising approaches of computer simulations of asphaltenes-based systems are determined

Scale-Dependent Miscibility of Polylactide and Polyhydroxybutyrate: Molecular Dynamics Simulations

Miscibility of polylactide (PLA) and polyhydroxybutyrate (PHB) is studied by the microsecond atomistic molecular dynamics (MD) simulations for the first time. The model and the simulation protocol were confirmed through comparison of the glass transition temperature (<i>T</i>_g) with experimental data. It was established that PLA and PHB are miscible on the basis of the Flory–Huggins theory. Analysis of the mobilities of PLA and PHB subchains revealed that the blends have two transitions to a glassy state at the length scale of a few Kuhn segments, which is in line with the predictions of the self-concentration model. At the same time at the larger length scale a single transition to a glassy state was observed, suggesting scale dependence of PLA and PHB miscibility. This scale dependence was confirmed through the evaluation of the interchain pair correlation functions