Conformationally asymmetric block copolymers

The standard parameters controlling AB diblock copolymer phase behavior are χN and f_A, where χ is an A-B segment interaction parameter, N is the overall degree of polymerization, and f_A is the volume fraction of the A block. Recently, it has been recognized that the ratio of the A and B statistical segment lengths a_A/a_B also represents another important parameter. Here, we theoretically examine the effects of this latter parameter on the phase behavior using the standard Gaussian chain model. Calculations are performed using both self-consistent field theory (SCFT) and strong segregation theory (SST). The ratio a_A/a_B is shown to have strong effects on order-order phase boundaries. Furthermore, it significantly affects the relative stability of the complex phases. In particular, it enhances the metastability of the perforated lamellar phase and may actually cause it to become an equilibrium structure. We also illustrate that varying a_Ala_B produces large changes in the relative domain spacings at order-order phase boundaries, which could strongly affect the kinetics of these transitions.