Reactive Molecular Dynamics Simulations of Self-Assembly of Polytwistane and Its Application for Nanofibers

Abstract

We investigated the self-assembly and mechanical properties of polytwistane (PT), particularly a seven-strand PT rope, using reactive force field-based molecular dynamics simulations at different temperatures. We show that upon self-assembly due to strong van der Waals interaction among PT units, PTs form a twisted structure (ropelike) with a twisting angle of ∼0.16 rad/nm at 300 K, which makes them mechanically stronger. The PT rope has high Young’s modulus (∼0.45 TPa) at 300 K. Interestingly, Young’s modulus increases with temperature for the seven-strand PT rope, whereas it decreases with temperature for a single-strand PT. This is because in the case of the seven-strand PT, the twisting angle also contributes to the elastic property of the PT rope and twisting depends on the temperature. We estimate a maximum load transfer of ∼1.1 and ∼3.3 nN to the central unit at 100 and 300 K, respectively. Hence, the amount of load transfer critically depends on the twisting in the rope. The fracture behavior of t...