  When two macromolecules come very near in a fluid, the surrounding molecules,
having finite volume, are less likely to get in between. This leads to a
pressure difference manifesting as an entropic attraction, called depletion
force. Here we calculate the density profile of liquid molecules surrounding a
disordered rigid macromolecules modelled as a random arrangement of hard
spheres on a linear backbone. We analytically determine the position dependence
of the depletion force between two such disordered molecules by calculating the
free energy of the system. We then use molecular dynamics simulations to obtain
the depletion force between stiff disordered polymers as well as flexible ones
and compare the two against each other. We also show how the disorder averaging
can be handled starting from the inhomogenous RISM equations.

Soft Condensed Matter;Disordered Systems and Neural Networks;Mesoscale and Nanoscale Physics;Statistical Mechanics;Chemical Physics