Lamellar Domain Spacing of Symmetric Linear, Ring, and Four-Arm- Star Block Copolymer Blends

In this study, we performed dissipative particle dynamics simulations of pure melts and blends of symmetric linear, ring, and four-arm-star block copolymers (BCPs), to investigate how their lamellar domain spacing (D) could be controlled. To address the finite polymerization degree (N) used in simulation, the four-arm stars were modeled using the detailed particle-based representation. The results of our simulations confirmed that for pure melts of linear and ring BCPs, the variation of the domain spacing with repulsion strength (delta a) is consistent with theoretical predictions. However, because of our use of particle-based representation of molecular structures, the values of D obtained for pure star BCP melts were larger than the theoretically predicted ones with the same N. Based on the variation in the profiles of the interfaces between the lamellar domains at different length scales, we quantitatively estimated the effects of thermal fluctuation such as interfacial roughness. Surprisingly, we found that the effects are larger with ring BCPs than with star or linear BCPs. Finally, we noted that for a polymer blend consisting of a combination of linear and nonlinear BCP melts with the same N, D decreases monotonically with the molar fraction of the ring or star polymer. Thus, given their resistance to thermal fluctuation effects, star BCPs are preferable to ring BCPs for adjusting the domain spacing of a polymer blend.