Computer simulation studies of molecular order in chromonic mesophases

par Fatima Chami

jeudi 17 déc. 2009, 11:00 → 12:00 Europe/Paris

Auditorium M. Vivargent (LAPTH)

Chromonic liquid crystals occur widely in aqueous dispersions of many formulated products such as pharmaceuticals and the dyes used in inkjet printing. They are also used in material science for fabricating highly ordered thin films and anisotropic carbons. Chromonic mesophases are usually formed in water from disk-like or plate-like molecules. Here, molecular self-assembly occurs into stacks, and the stacks are then able to pack to form liquid crystalline phases. Unlike many lyotropic liquid crystals, self-assembly is not mediated by the hydrophobic effect, i.e. entropic interactions but is enthalpy driven. Results are presented from atomistic simulations of a chromonic stack for the molecule edicol (sunset yellow) in water, looking at the ordering of edicol molecules in the columns. Results are also presented for quantum predictions of NMR shielding. Our simulations have also allowed predictions of free energy changes on association of molecules into stacks, allowed us to study the influence of salt on aggregation, and allowed preliminary predictions for the structure of a bulk N-phase. Finally, simulation results are linked to recent experimental measurements in solution, which are also aimed at understanding how self-assembly occurs in chromonics.