Entropy Reduced Charge Transport and Energy Loss in Interfacial Zones of Polymer Nanocomposites

Polymer nanocomposites have higher energy storage density, much lower conductivity, and energy loss than the polymer matrices. The excellent performance may be originated from the deep-level localized states introduced by the interfacial zones between nanofillers and polymer matrices. However, the essential relation between the deep-level localized states and the composition, architecture, and configuration of polymer chains is still not clear. We investigate the temperature dependences of electrical conductivities of three types of energy storage polymer nanocomposites and find that they all obey the Meyer-Neldel (MN) compensation rule and the prefactor has an exponential relationship with the MN energy. It is found that the kinetic energy of electrons in the extended states of nanocomposites is the MN energy, which is related to the excitation of electrons by optical phonons. We propose to redefine the energy of localized states by the energy of optical phonons and the entropy of molecular conformations. It is found that the shape parameter of localized state distribution is related to the optical phonons and controlled by the composition, structure, and configuration of polymer chains, while the density of localized states is determined by the conformation and aggregate structure. We propose an optical phonon and entropy activated charge transport model, and the obtained conductivity equation is consistent with the experimental results. The entropy of molecular conformations can be used as a key factor to tailor the conductivity and energy loss of polymer nanocomposites. It provides a new perspective to study how to improve the energy storage performance of polymer nanocomposites.