**Short-time elasticity of polymer melts: Tobolsky conjecture and
heterogeneous local stiffness**

S Bernini and D Leporini, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 53, 1401-1407 (2015).

DOI: 10.1002/polb.23783

An extended molecular-dynamics study of the short-time glassy elasticity exhibited by a polymer melt of linear fully-flexible chains above the glass transition is presented. The focus is on the infinite-frequency shear modulus G manifested in the picosecond time scale and the relaxed plateau G(p) reached at later times and terminated by the structural relaxation. The local stiffness of the interactions with the first neighbors of each monomer exhibits marked distribution with average value given by G. In particular, the neighborhood of the end monomers of each chain are softer than the one of the inner monomers, so that G increases with the chain length. G(p) is not affected by the chain length and is largely set by the nonbonding interactions, thus confirming for polymer melts the conjecture formulated by Tobolsky for glassy polymers. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1401-1407

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