  We use optical and fluorescence microscopy, densitometry, cryo-transmission
electron microscopy (cryo-TEM), spectroscopy, and synchrotron X-ray scattering,
to study the phase behavior of the reversible self-assembled chromonic
aggregates of an anionic dye Sunset Yellow (SSY) in aqueous solutions crowded
with an electrically neutral polymer polyethylene glycol (PEG) and doped with
the salt NaCl. PEG causes the isotropic SSY solutions to condense into a
liquid-crystalline region with a high concentration of SSY aggregates,
coexisting with a PEG-rich isotropic (I) region. PEG added to the homogeneous
nematic (N) phase causes separation into the coexisting N and I domains; the
SSY concentration in the N domains is higher than the original concentration of
PEG-free N phase. Finally, addition of PEG to the highly concentrated
homogeneous N phase causes separation into the coexisting columnar hexagonal
(C) phase and I phase. This behavior can be qualitatively explained by the
depletion (excluded volume) effects that act at two different levels: at the
level of aggregate assembly from monomers and short aggregates and at the level
of inter-aggregate packing. We also show a strong effect of a monovalent salt
NaCl on phase diagrams that is different for high and low concentrations of
SSY. Upon the addition of salt, dilute I solutions of SSY show appearance of
the condensed N domains, but the highly concentrated C phase transforms into a
coexisting I and N domains. We suggest that the salt-induced screening of
electric charges at the surface of chromonic aggregates leads to two different
effects: (a) increase of the scission energy and the contour length of
aggregates, and (b) decrease of the persistence length of SSY aggregates.
