A stretch-based model for flow-enhanced nucleation of polymer melts

Abstract

A phenomenological model for flow-enhanced nucleation in crystallizing polymers is developed and validated by short-term shear experiments [Housmans et al., Macromolecules 42, 5728–5740 (2009); Hristova et al., Proceedings of the 228th ACS National Meeting, Philadelphia (2004)]. The model extends earlier work on flow-induced oriented crystallization [Custódio et al., Macromol. Theory Simul. 18, 469–494 (2009); Peters et al., Macromol. Symp. 185, 277–292 (2002); Peters, Polymer Crystallization: Observations, Concepts and Interpretations, edited by G. Reiter and J.-U. Sommer (Springer, Berlin, 2003), pp. 312–324; Zuidema, Ph.D. thesis, Technische Universiteit Eindhoven (2000); Zuidema et al., Macromol. Theory Simul. 10, 447–460 (2001)] to flow-enhanced pointlike nucleation, which can lead to number densities of spherulites multiplied by orders of magnitude. Excellent agreement between simulations and experimental data is obtained, for a range of rates and durations of shearing, with only two adjustable parameters: a prefactor to the creation rate of flow-induced nucleation precursors and a parameter that governs their influence on the relaxation dynamics of the high-molecular weight (HMW) fraction of the melt. The two main conclusions of this paper are, first, that the creation of flow-induced precursors is driven by the average stretch, not by the average orientation, of the primitive paths of chains in the HMW tail of the molecular weight distribution, and second, that nucleation of these precursors is impeded by flow.