Stretching and breaking of PEO nanofibres. A classical force field and ab initio simulation study

Abstract

Nanometric bundles are considered in nearly atomistic detail, studying the effect of chain–chain interactions on the mechanical properties.

A Legendre–Fenchel Transform for Molecular Stretching Energies

“…The force elongation relation for the Legendre-Fenchel transformed energy can be obtained by the derivative of G LF with respect to f , cf. Equation (17). This monotonically increasing curve is shown with a black dotted line in Figure 4a-c 17) is compared to the force-elongation curves from Figure 1.…”

“…We use the same model as some of us have used previously [11,17] to investigate molecular stretching of poly-ethylene oxide (PEO) on the form CH 3…”

“…The temperature was set to 300 K during sampling, and was controlled by a Langevin thermostat with a relaxation time of 1 ps and a time step of 1 fs. The initial configurations were exposed to a simulated annealing protocol prior to sampling, in an attempt to capture a representative portion of the phase space [17,23]. The presented data are averaged over 5 ns for 200 samples.…”

“…where p j ≡ p j , m j is the mass of bead j, and V(r 1 , ..., r N ) is the potential interaction. In our previous work [11,17], we gave an explicit expression for the interaction potential with contributions from bond stretching, bending, and torsion. The polymer is controlled either in the isometric ensemble by fixing the end-to-end distance x ≡ |r N − r 1 |, or in the isotensional ensemble by applying a stretching force f ≡ |f N − f 1 |.…”

Fatigue and failure of a polymer chain under tension

“…The breaking time τ is a stochastic variable, since the dynamics at any given temperature induces random fluctuations in the separation of the particles until one (or more) reaches a breaking point. Many studies considered this problem under one guise or another, mainly with the aim of offering a theory for the mean breaking time, or the mean rate of breaking τ −1 where the angular brackets represent an average over many realizations [4][5][6][7][8][9][10][11][12]. It turns out (and see below) that the distribution of breaking rates is not at all sharply peaked, and one should worry about the tail of the distribution that represents rare, but potentially catastrophic, fast rates of breaking (or, mutatis mutandi, short times for failure).…”