Role of Chain Semiflexibility and Density Fluctuations in Diblock Copolymer Phase Behavior

Block copolymer semiflexibility can arise from aromatic backbone and pi-bond conjugation in organic electronics applications. This poses challenges to apply theoretical predictions to experimental systems, since chain semiflexibility along with density fluctuation effects can dramatically influence the phase behavior of block copolymers. We investigate the phase behavior of a semiflexible diblock copolymer melt using random phase approximation and renormalization group theory. We present a chain rigidity-dependent free energy functional up to quartic order in density fluctuations. One-loop renormalization is used to account for fluctuation effects due to finite effective chain concentration. Using this approach, we examine the order-disorder transitions (ODT) and phase diagrams of semiflexible diblock copolymers beyond mean-field theory. We show that both the renormalized ODT Flory-Huggins parameters and phase diagrams are strongly dependent on diblock copolymer chain rigidity. Such theoretical formulation of semiflexible block copolymers broadens the applicability of theory to study nanostructured polymeric materials.