Molecular Simulation of the Phase Behaviour of Attractive Rod-Like Polymers

Through a hierarchical modelling scheme, we determine a phase diagram of attractive rod-like polymers in three dimensions, comparing them with their freely jointed polymer counterparts [1,2]. Rod-like polymers are modelled as linear chains of tangent hard spheres whose chain stiffness is governed by a tuneable harmonic potential for the bending angle [3]. Employing the Simu-D suite [4], extensive Monte Carlo simulations provide a surprisingly rich collection of distinct crystal polymorphs, which can be finely tuned according to the range of attraction. These crystal polymorphs, identified by the Characteristic Crystallographic Element (CCE) norm [5], include face-centred cubic, hexagonal close-packed, simple hexagonal, and body-centred cubic structures and their combinations, as well as the establishment of the Frank–Kasper phase for freely jointed chains. Furthermore, employing the concept of cumulative neighbours of ideal crystals, a simple geometric model is proposed as a function of the range of attraction to accurately predict most of the observed structures and the corresponding transitions [2]. A geometrical analysis is provided of the characteristics of the self-assembled polymer clusters and crystals under conditions corresponding to a vacuum. Therefore, the present study demonstrates, at a fundamental level and in a highly idealised model, the capacity to fine-tune a single interaction parameter to employ for the design of polymer crystals with tailored morphologies.

[1] M. Herranz, M. Santiago, K. Foteinopoulou, N.C. Karayiannis and M. Laso, Polymers 12, 1111 (2020).

[2] M. Herranz, C. Pedrosa, D. Martínez-Fernández, K. Foteinopoulou, N.C. Karayiannis and M. Laso, Phys. Rev. E 107, 064605 (2023).

[3] D. Martínez-Fernández, M. Herranz, K. Foteinopoulou, N.C. Karayiannis and M. Laso, Polymers 15, 551 (2023).

[4] M. Herranz, D. Martínez-Fernández, P. Ramos, K. Foteinopoulou, N.C. Karayiannis and M. Laso, Int. J. Mol. Sci. 22, 12464 (2021).

[5] P. Ramos, M. Herranz, K. Foteinopoulou, N.C. Karayiannis and M. Laso, Crystals 10, 1008 (2020).