Journal of Non-Newtonian Fluid Mechanics, Vol.94, No.1, 37-45, 2000
The role of molecular folds and'pre-conditioning' in the unraveling of polymer molecules during extensional flow
Recent single-molecule DNA studies and simulations of bead-spring chains in an extensional flow device show that molecular stretching is impeded significantly at high fluid strain rates by the formation of folded molecular conformations [T.T. Perkins, D.E. Smith, S. Chu, Science 276 (1997) 2016-2021; D.E. Smith, S. Chu, Science 281 (1998) 1335-1340; R.G. Larson, H. Hu, D.E. Smith, S. Chu, J. Rheol. 43 (1999) 267-304]. We show using bead-spring Brownian dynamics simulations that the formation off olds is very sensitive to the initial molecular configuration, and can be largely avoided in extensional flow by pre-shearing the molecules prior to imposition of the extensional flow. Imposing the shearing flow simultaneously with the extensional flow has little or no effect on fold formation.