Conclusions

In this study of polymer nano-particles using molecular dynamics simulations we have analyzed the thermal and mechanical properties ofthe particles generated with up to 60,000 Two groups of atoms were singled out for analysis: those in the central and adjacent fluid slices at the beginning ofthe simulation The fraction ofkinetic energy in the z direction was followed in each group of atoms. Typical results are shown in Fig. 2. The fraction of z kinetic energy steadily decreases in the central region atoms, averaging about the thermal equilibrium value, 1/3, within less than 5 ps. The adjacent region atoms suddenly gain z kinetic energy within about the first 0.1 ps and then a decreasing trend similar to that for the central region atoms. No coherent transfer of z kinetic energy is observed. In short, the motion very rapidly thermalizes, which is consistent with the results of visualization. In several simulations, positions of every fluid atom were saved every 0.05 ps. The movies showed that within 2 ps, the atoms in the initial plug essentially interspersed themselves within the adjacent fluid volume and then randomly dispersed. This behavior was observed at each nanotube radius. atoms. It is found that surface effects provide interesting properties that are different from those of the bulk polymer system. In particular, the melting point and glass transition temperature were found to be dramatically dependent on the size of the polymer particles. This study also demonstrated that the nano-scale PE particles have dynamical flexibility and behave like an elastomer. The result is quantified by the fractal dimension and compressive modulus. We are currently extending this model and methodology to larger size particles and other types of polymer systems to study the interfacial tension between incompatible polymers, shear flow effects, and thermal properties of blended polymer particles.29 The molecular dynamics simulations used here should provide useful insights to explain and predict the properties and behavior of ultra fine polymer particles to be used in future new materials and devices.

Acknowledgments

Research sponsored by the Division of materials Sciences, Office of Basic Energy Sciences, US Department of Energy under Contract DE-AC05-960R22464 with Lockheed Martin Energy Research. K.F. is supported by the Postdoctoral Research Associates Program administered jointly by Oak Ridge National Laboratory and the Oak Ridge Institute for Science and Education.

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