(435g) Coarse-Grained Molecular Dynamics Study of the Self-Assembly of Triblock Bolaamphiphiles with SAFT-? Mie CG Forcefield

T-shaped triblock bolaamphiphiles (TBAs) constitute a family of thermotropic liquid crystals that exhibit a plethora of columnar and network phases. Complex two-dimensional tiling patterns have been observed both in experiments [1] and simulations [2-6]. Given the length-scales of these complex patterns and long equilibration times required to observe self-assembly, previous simulation studies have relied on model systems to phenomenologically investigate the mesophase behaviour of this family of liquid crystals.

This work employs coarse-grained models of TBAs using the SAFT-γ Mie CG forcefield [7] to develop an accurate in silico representation of the aforementioned molecules. For each functional group, namely the phenyl rigid backbone, glycerol end groups and the flexible alkyl side chains, a top-down approach is used to fit Mie potential parameters to experimental data using SAFT-γ Mie equation of state (EoS). Subsequently, molecular dynamics simulations using the model developed are carried out to predict the mesophase behaviour of recently investigated swallow-tail TBAs. [8]

Poppe et al. [8] have observed very complex tiling patterns of TBAs by changing the structure of the lateral side chains from a single chain of 20 carbons to a swallow-tail whilst conserving the total number of carbons. Given the susceptibility of these molecules to changes in phase behaviour with the slightest changes in the morphology of the lateral side-chains, swallow-tail TBAs are ideal candidates to assess the predictability of the proposed potential parameters in accurate modelling of these liquid crystals.

A comparison between the experimental results and simulations is presented, with the proposed model correctly predicting the morphology of the honeycomb and the pentagonal-hexagonal columnar phases. Moreover, inter-column distances and columnar-isotropic transition temperatures are calculated for every system. For the hexagonal columnar phase, an inter-column distance of 4.2 nm is correctly predicted with a slight under-prediction in the columnar-isotropic transition temperature. This is also observed in the other columnar phases studied in this work.

References:

[1] C. Tschierske et al, Interface Focus, 2, 669-680 (2012)

[2] A. J. Crane et al, Soft Matter, 4, 1820-1829 (2008)

[3] M. A. Bates and M. Walker, Soft Matter, 5, 346–353 (2009)

[4] M. A. Bates and M. Walker, Molecular Crystals and Liquid Crystals, 1, 525, (2010)

[5] X. Liu et al, J Phys Chem B., 117, 9106-9120 (2013)

[6] Y. Sun et al, Soft Matter, 13, 8542-8555 (2017)

[7] E. A. Müller and G. Jackson, Ann. Rev. Chem. & Biomolec. Eng. 5, 405-427 (2014)

[8] S. Poppe et al, Nature Communications, 6, Article Number: 8637 (2015)