Nonlinear Relaxation Behavior of Diblock Copolymer Micellar Dispersions: Effects of Corona−Matrix and Corona−Corona Entanglements

Abstract

The nonlinear relaxation modulus was examined for styrene−isoprene (SI) diblock copolymer micelles having rigid (glassy) S cores and flexible I corona blocks. These micelles, being dispersed randomly in entangling and/or nonentangling matrices of homopolyisoprene (hI), exhibited fast and slow relaxation processes. The fast process reflected the orientational relaxation of the corona I blocks, and the slow process detected the relaxation of the Brownian stress σB. This σB reflected the anisotropy of micelle distribution and relaxed through the micelle diffusion. The fast and slow processes exhibited the nonlinear damping of the modulus under large step strains (γ), and the time-strain separability was observed for both processes in either the entangling or nonentangling matrices. For the fast process, the damping function hf(γ) hardly changed with the SI micelle concentration CSI and matrix molecular weight Mmatrix and was close, in magnitude, to h(γ) of homopolymers. The nonlinearity of the corona relaxat...