|Résumé :||Statics, dynamics, rheology and scission-recombination kinetics of self-assembling linear micelles are investigated at equlibrium state and under shear flow by computer simulations using a newly proposed mesoscopic model. We model the micelles as linear sequences of Brownian beads whose space-time evolution is governed by Langevin dynamics. A Monte Carlo algorithm controls the opening of a bond or the chain-end fusion. A kinetic parameter omega modelling the effect of a potential barrier along a kinetic path, is introduced in our model.
For equilibrium state we focus on the analysis of short and long time behaviors of the scission and recombination mechanisms. Our results show that at time scales larger than the life time of the average chain length, the kinetics is in agreement with the mean-field kinetics model of Cates. By studying macroscopic relaxation phenomena such as the average micelle length evolution after a T-jump, the monomer diffusion, and the zero shear relaxation function, we confirm that the effective kinetic constants found are indeed the relevant parameters when macroscopic relaxation is coupled to the kinetics of micelles.
For the non-equilibrium situation, we study the coupled effects of the shear flow and the scission-recombination kinetics, on the structural and rheological properties of this micellar system. Our study is performed in semi-dilute and dynamically unentangled regime conditions. The explored parameter omega range is chosen in order for the life time of the average size chain to remain shorter than its intrinsic (Rouse) longest relaxation time. Central to our analysis is the concept of dynamical unit of size Lambda, the chain fragment for which the life time tau_Lambda and the Rouse time are equal. Shear thinning, chain gyration tensor anisotropy, chain orientation and bond stretching are found to depend upon the reduced shear rate Beta_Lambda=gamma dot*tau_Lambda while the average micelle size is found to decrease with increasing shear rate, independently of the height of the barrier of the scission-recombination process.