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RESEARCH PRODUCT

Dielectric Relaxation of a Polybutadiene Melt at a Crystalline Graphite Surface: Atomistic Molecular Dynamics Simulations

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Dielectric experiments are an indispensable tool to further our understanding of the relaxation behavior of polymers, not only in bulk samples but also in confined situations. A chemically realistic Molecular Dynamics simulation, in which all information about molecular motions is available, can shed light onto the questions of heterogeneity and anisotropy of the underlying molecular relaxation processes which lead to the ensemble averaged experimental dielectric signal. In this contribution, we present a careful analysis of the dielectric response of a weakly polar and confined polymer, 1,4-polybutadiene between graphite walls. The relaxation of the segmental dipole moments was obtained in the time domain and transformed into frequency (Fourier) domain as well as the relaxation time (Debye) domain to highlight the differences between the two types of analysis. A particular bonus of the simulation is that detailed spatially resolved information on structure and dynamics of the confined system is available. We determine the influence of the confinement on the dielectric relaxation and show that for this system the apparent glass transition temperature of a confined film is independent of its thickness even on the scale of a few nanometers.