Kinetics and dynamics of wormlike micelles under shearC.-C. Huang1, 2, H. Xu1 and J. P. Ryckaert2
1 Laboratoire de Physique des milieux denses, Université Paul Verlaine-Metz - 1 bd Arago, F-57078 Metz cedex 3, France
2 Physique des Polymères, Université Libre de Bruxelles - Campus Plaine, CP 223, B-1050 Brussels, Belgium
received 15 June 2007; accepted in final form 8 January 2008; published March 2008
published online 7 February 2008
Mimicking giant cylindrical micelles in solution, self-assembled linear polymers are studied by Langevin dynamics in shear flow. The kinetics of chain scission (with rate ks per bond) and chain end recombination (with rate kr) is modelled by associating to each monomer two arms for binding. A switch of pair potentials (from bounded to unbounded or vice versa) is tried with a fixed attempt frequency per arm modelling the effect of a potential barrier along a reaction path. The opening of a selected bond or the bonding between two selected free ends are accepted or not according to a Monte Carlo algorithm. We are interested in 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 with an average chain size L0. The explored range is chosen sufficiently high for the lifetime 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 , the chain fragment for which the lifetime and the Rouse time are equal. Shear thinning, chain orientation and bond stretching are found to depend upon the reduced shear rate , 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.
83.60.Rs - Shear rate-dependent structure (shear thinning and shear thickening).
83.80.Qr - Surfactant and micellar systems, associated polymers.
82.20.Wt - Computational modeling; simulation.
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