Simulation of main chain liquid crystalline polymers using a Gay-Berne/Lennard-Jones hybrid model

Main chain liquid crystalline polymers (MCLCP) offer strong potential to exhibit auxetic properties. However, the first synthesized molecules did not show the expected results. To address this issue, simulation provides an interesting advantage as it can grasp the molecular reasons why the auxetism is not reached, and thus it can guide the synthesis of successful candidates. However, the crucial step of validation is mandatory. In this study, we report the simulation of MCLCP at the coarse-grained level. Interactions are represented by an hybrid GayBerne/Lennard Jones (GB/LJ) potential which is particulary adapted in the simulation of anisotropic systems. Energies stemming from different configurations of pairs of ellipsoids are computed at the MP2 level, and are fitted using the GB potential. The methylene groups are represented by spheres whose interactions are depicted by the LJ potential. Molecular dynamics in the NPT ensemble (number of particles, pressure and temperature are kept constant) are thus carried out beginning at 800 K to 375 K, by cooling the system by 25 K steps. It is shown that the smectic A phase emerges at about 500 K, and the smectic B phase at about 425 K. Such mesophases occur without the use of any external stimulus. These findings pave the way to simulate LCP which have been specifically designed to potentially exhibit auxetic properties.