Comparison of Brownian dynamics simulations with microscopic and light-scattering measurements of polymer deformation under flow

Using Brownian dynamics simulations, we predict the deformation of a polymer coil in dilute solution and compare the results to direct measurements for DNA molecules and for polystyrene. For DNA, optical microscopy measurements of Smith and Chu yield measurements of [x], the average projected length of the molecule onto the flow direction as a function of shear rate, while for dilute polystyrene solutions, light scattering experiments yield [R-g(2)](1/2), the root-mean-square radius of gyration. Both measurements of deformation, [x] and [R-g(2)](1/2), are obtained from the simulations using input parameters required to match the molecular characteristics of both the DNA and the polystyrene solutions used in the experiments. We find that while the agreement between the simulations and the measurements of coil deformation for DNA is excellent, for polystyrene the measured deformation is much less than predicted.