Molecular Dynamics Simulations of Polymeric Fibre Bundles under Tensile Load

Bundles of polymeric materials play essential and ubiquitous roles in biological systems, and o en display remarkable mechanical properties [1]. By utilizing non-equilibrium molecular dynamics simulations to pre- form force controlled and length controlled virtual stretching experiments of polymeric bre bundles one may get valuable insight into the mechanical properties of nano brous materials. A minimalistic reactive force eld is constructed from existing force elds to investigate the yield behavior of the samples [2]. e supra-molecular structure of brils in nanometric bundles is studied, which have been shown experimentally to have great impact on e.g. the Young’s modulus of the bundles [3]. e chains in the bundle typically self or- ganize to a semi-crystaline hexagonal pa ern with entropically induced defects due to non-zero temperatures, with higher degree of amorphicity for low external forces. e main material investigated here is polyethylene oxide (PEO), a polyether compound with applications ranging from industrial manufacturing to medicine. e simple chemical composition makes it well suited as a starting point for the study of the general behavior of polymeric bre bundles, and this procedure of virtual stretching is directly applicable to more complex structures such as cellulose or collagen with and without the presence of third species, such as room temperature ionic liquids and aqueous environments. e simulations are carried out for a range of sizes to study nite size e ects. e thermodynamic potentials of the bundles are studied in more detail. e smallest systems under in- vestigation consists of single molecules of PEO with 32 units, and on this scale it is still debated whether a non-equilibrium thermodynamic description even exists. According to the theory of Hill (small system thermodynamics), the thermodynamic functions cease to be extensive at small length scales. ey obtain ad- ditional terms, from surface or line energy contributions. Strøm, Schnell and Kjelstrup have previously found a scaling law between the thermodynamic and the molecular limit [4]. is indicates that the thermodynamic laws will indeed apply to the molecular level, provided that we use the additional terms arising from the sys- tem smallness. It is an aim of the project to verify the theoretical formulation of Rubi et al. [5]. is may have a large fundamental impact on how one can describe biomolecular and other events related to energy conversion on the small scale. References [1] N. G. McCrum, C. P. Buckley, C. B. Bucknall, Principles of Polymer Engineering, Oxford University Press, Oxford, New York (1997). [2] C. Chen, P. Depa, V. G. Sakai, J. K. Maranas, J. W. Lynn, I. Peral & J. R. D. Copley. J. Phys. Chem. 124 (2006). [3] A. Arinstein, M. Burman, O. Gendelman, E. Zussman, Nat. Nanotechnol. 2, 59 (2007). [4] B. A. Strøm, J.-M. Simon, S. K. Schnell, S. Kjelstrup, J. He & D. Bedeaux. J. Phys. Chem. 19 (2017). [5] J. M. Rubi, D. Bedeaux & S. Kjelstrup, J. Phys. Chem. 110 (2006).