Simulation of polymer chains in elongational flow. Steady-state properties and chain fracture

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Abstract
The behavior of polymer chains in steady, uniaxial elongational flows is studied using the Brownian dynamics simulation technique. Two different types of chain models are considered. One is the bead-and-spring Rouse chain and the other is a chain with breakable connectors that obey a Morse potential. The dynamics of Rouse chains and Morse chains is simulated both without and with hydrodynamic interaction (HI) between chain elements. From the simulated trajectories, steady-state properties such as chain dimensions and elongational viscosities are calculated. When HI is accounted for by using the Rotne–Prager–Yamakawa tensor, the calculated dimensions and viscosities are appreciably lower than when it is neglected. Carrying out simulations with varying elongational rate, it is possible to observe stretching and finally the fracture of the polymer chains. The critical elongational rate, corresponding to infinite elongation in the case of Rouse chains, and the fracture of the Morse chains has been characterized as a function of chain length. When the short length of the simulated chains is accounted for adequately, we find that the elongational rate needed for fracture ε̇f scales with molecular weight M as ε̇f∝M−2. This result, which had already been predicted rigorously without HI, holds in practice as well when hydrodynamic interaction is considered.