Dynamic scaling in dilute polymer solutions: The importance of dynamic correlations

Abstract

The swelling αH of the hydrodynamic radius of a polymer, obtained using Brownian dynamics simulations of the continuum Edwards model, is found to obey a crossover in the excluded-volume parameter z, which is significantly different from that observed for the swelling αg of the radius of gyration. It is shown that this difference arises due to contributions from dynamic correlations to the diffusivity, which are ignored in the commonly used definition of hydrodynamic radius based on the Kirkwood expression. Simulated values of αH are found to be in remarkable agreement with experimental measurements

Viscosity Radius of Polymers in Dilute Solutions: Universal Behavior from DNA Rheology and Brownian Dynamics Simulations

“…This approach, however, also does not result in an improved prediction of the universal crossover function for α H [18].…”

“…Since the parameter z * → 0 in this limit, the long chain limit of the model corresponds to the Edwards continuous chain model with a delta function excluded volume repulsive potential [45]. As mentioned in Section I, by accounting for fluctuating hydrodynamic and excluded volume interactions in this manner, Sunthar and Prakash [18] have obtained a quantitatively accurate parameter free prediction of α H as a function of z. Here, we show that this approach can also be used to successfully predict universal properties related to the zero shear rate viscosity of dilute polymer solutions.…”

“…Notably, however, the universal curve for α g (which is a ratio of static properties), is significantly different from the universal curves for α H and α η , which are ratios of dynamic properties [6][7][8][9]. There have been many attempts to understand the origin of this difference in crossover behaviour, and to predict analytically and numerically, the observed universal curves [4,[10][11][12][13][14][15][16][17][18] (see Ref. 19 for a recent review).…”

“…By accounting for fluctuating hydrodynamic and excluded volume interactions in the asymptotic long chain limit, Prakash and coworkers have been able to obtain quantitatively accurate, parameter free predictions of α g and α H as functions of z [18,23].…”

Fluctuating lattice-Boltzmann model for complex fluids

“…Dünweg et al 70 have done extensive work on measuring R g /R I with the result 1.63 ± 0.01 for a bead-spring model in continuum space (in this case they use R I as the static hydrodynamic radius defined through 1/R I = m =n 1/|r m − r n | ). Sunthar and Prakash 71 have pointed out that the static measure R I is systematically larger than the dynamic hydrodynamic radius present in Eq. (A1) as R H = R g /A.…”