The "solvent" effect of short arms on linear and nonlinear shear rheology of entangled asymmetric star polymers.

This study examines the influence of the short arms in model asymmetric 3-arm star polymers, in which the short arm is unentangled while the other two long arms are entangled, on linear and nonlinear shear rheological behavior. As increasing the short arm length of the asymmetric star polymers, the linear viscoelastic rubber plateau decreases, indicating the relaxed short arms act as "solvent" that dilute the star polymers. This idea is examined by the relationship between the plateau moduli of polymer solutions G N (φ) and the corresponding polymer melts G N (1) for entangled linear polymers, G N (φ) = G N (1) φ 1+α, where φ is the volume fraction of the polymer. The "solvent" effect of the short arms is also supported by the nonlinear rheology results showing weaker damping function and larger peak strain at stress overshoot. With the above clarification of the short-arm contributions, this work provides a guidance of molecular design for tuning linear and nonlinear rheology of star polymers. [Display omitted] • The influence of the short arms in model asymmetric star polymers on shear rheology is identified. • The short arms act as "solvents", leading to lower plateau modulus just like entangled polymer solutions. • The dilution effect of the short arms on nonlinear rheology is represented by larger peak strain and weaker damping response. [ABSTRACT FROM AUTHOR]