Phase behavior of rigid, amphiphilic star polymers

We determine the phase behavior of rigid, amphiphilic diblock copolymer stars in solution, by employing a lattice model and applying Grand Canonical Monte Carlo simulations as well as histogram reweighting techniques. Previous studies on these systems [C. Koch et al., Mol. Phys., 2011, 109, 3049] have found that for fully flexible chains with a moderate functionality ranging from f = 3 to f = 10 and with a solvophilic A-block smaller than or equal to the solvophobic B-block, the solution undergoes a liquid-gas macrophase separation with a well-defined critical point. We find that the introduction of chain rigidity alters the critical parameters: the higher the stiffness, the higher the critical temperature T_c and the lower the critical density _c. Furthermore, we find that for high rigidities and densities beyond _c, the molecules arrange in cubic, columnar and lamellar ordered phases whose domain of stability depends on molecular architecture and block incompatibility. For even higher densities the system remelts again into another fluid phase. The resulting rich phase diagrams of star polymers that feature amphiphilicity and high rigidity are a manifestation of the character of these hybrid molecules as polymer-based, soft patchy colloids.