Intramolecular relaxation of block copolymeric rings in dilute solutions

The viscoelastic properties of block copolymeric rings are investigated within the framework of optimized Rouse-Zimm theory. A multiresolution bead spring model is used to depict ring block copolymers, which accounts for the variable sizes of the beads connected via different harmonic springs. The hydrodynamic interactions between these beads are approximated using the preaveraged Oseen tensor. The viscoelastic properties of these ring block copolymers are evaluated from the relaxation rates of their respective normal modes. The relaxation dynamics of ring block copolymers are enhanced and retarded in the low and high frequency regimes, respectively, with an increase in the monomeric block length. The storage modulus for ring diblock copolymers reveals a quasi-plateau regime, indicating a solid-like response, whereas the loss modulus exhibits a bimodal pattern due to a difference in the relaxation dynamics of the A- and B-type monomeric domains, unlike the ring homopolymers and multiblock copolymers. The loss tangent displays two quasi-plateaus corresponding to two dynamically distinct monomeric domains. Homopolymeric rings are maximally compact compared to those of ring multiblock and diblock copolymers. The compactness of the ring diblock copolymers decreases with an increase in the size of the B-type monomers. The characteristic overall relaxation time of ring alternating copolymers is lower than that of ring diblock copolymers, indicating a slower dynamics that spans over different time scales. The ring size has no effect on the characteristic overall relaxation time of the ring diblock copolymers unlike that of the ring alternating copolymers.