Abstract
New coarse-grained models are introduced for a non-ionic chromonic molecule, TP6EO2M, in aqueous solution. The multiscale coarse-graining (MS-CG) approach is used, in the form of hybrid force matching (HFM), to produce a bottom-up CG model that demonstrates self-assembly in water and the formation of a chromonic stack. However, the high strength of binding in stacks is found to limit the transferability of the HFM model at higher concentrations. The MARTINI 3 framework is also tested. Here, a top-down CG model is produced which shows self-assembly in solution in good agreement with atomistic studies and transfers well to higher concentrations, allowing the full phase diagram of TP6EO2M to be studied. At high concentration, both self-assembly of molecules into chromonic stacks and self-organisation of stacks into mesophases occurs, with the formation of nematic (N) and hexagonal (M) chromonic phases. This CG-framework is suggested as a suitable way of studying a range of chromonic-type drug and dye molecules that exhibit complex self-assembly and solubility behaviour in solution.
Highlights
Chromonics form a fascinating field of soft matter in which the self-assembly process is fundamentally different from conventional lyotropic liquid crystalline materials.[1,2,3] Chromonic mesogens are typically composed of rigid or semi-rigid diskshaped aromatic cores, which are solubilized in water through the addition of pendant hydrophilic groups
For both aggregate and mesophase formation to occur in the right concentration and temperature regime, a very delicate balance must be satisfied between different interactions in the system
The potential of mean force was calculated according to eqn (2), which includes a contribution arising from the increased rotational entropy at higher separation distances
Summary
Chromonics form a fascinating field of soft matter in which the self-assembly process is fundamentally different from conventional lyotropic liquid crystalline materials.[1,2,3] Chromonic mesogens are typically composed of rigid or semi-rigid diskshaped aromatic cores, which are solubilized in water through the addition of pendant (usually ionic) hydrophilic groups. We introduce new coarse-grained models for TP6EO2M, with the aim of reproducing the key features of self-assembly in solution and demonstrating chromonic mesophase formation. Such models are challenging to produce: stack formation occurs over periods of tens, or in most cases, hundreds of nanoseconds; and mesophase formation occurs on considerable longer time scales.
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