Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives

We investigate influence of different ionic additives on the phase behaviour and scalar order parameter of lyotropic chromonic nematic liquid crystals formed by the molecules representing derivatives of indanthrone. KI, (NH4)2SO4 and NaCl salts increase biphasic nematic region on the temperature-concentration phase diagram, whereas the scalar orientational order parameter is hardly sensitive to their presence. We suggest that these changes are attributed to increase in the ag-gregate length and polydispersity of the latter, while the interaction between ag-gregates remains unaffected. The Na2SO4 salt lowers anomalously the measured value of the scalar order parameter to 0.42, for which the nematic phase should not exist. We address this anomaly to modification of the shape of chromonic aggregates due to growing of side chains within the rod-like aggregates. The NH4Cl salt does not affect the phase diagram and the scalar order parameter of Blue 250 chromonematic.