  We have developed a class of idealized models of chromonic molecules which
are miscible in water, but which can form aggregates which in turn organize
into lyotropic liquid crystal (LC) phases. By carrying out Monte Carlo
simulation in a binary mixture of model chromonic and water molecules, we have
studied the effect of concentration and molecular shape on the nature of
resulting mesophases. We have also computed the free energy associated with the
formation of chromonic columnar aggregates by umbrella sampling. Our free
energy computation helps us to verify the isodesmic behavior which is
characteristic of chromonic systems. For isodesmic behavior the addition of
each chromonic molecule to the columnar aggregates is accompanied by a constant
free energy increment and the net free energy decreases with increasing column
length.
