Anisotropic friction and excluded volume effects in freely jointed bead–rod polymer chain models

Xu, Zhi Ming; Kim, S.; Pablo, Juan J. de

doi:10.1063/1.467383

Cited by 16 publications

(11 citation statements)

References 22 publications

(2 reference statements)

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“…This phenomenon has been reported before for Brownian chains in an anisotropic, hydrodynamic continuum, 37 for fully flexible chains in a melt, 2 and for rigid chains in a hydrodynamic continuum in the vicinity of a wall.…”

Section: Configurational Analysismentioning

confidence: 82%

Rheological, thermodynamic, and structural studies of linear and branched alkanes under shear

Khare¹,

Pablo²,

Yethiraj³

1997

The Journal of Chemical Physics

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The rheological, thermodynamic, and structural behavior of linear and branched alkanes in simple shear is investigated using nonequilibrium molecular-dynamics simulation of united atom model fluids. Our results for the zero-shear viscosity of pure linear alkanes as well as mixtures of alkanes are in reasonable agreement with experiment. Simulation results for intermediate molecular weight linear alkanes indicate that the simple models employed here are capable of describing the pressure and temperature dependence of the viscosity. More importantly, our calculations indicate that addition of short, flexible branches to alkanes leads to a viscosity enhancement of a factor of 2 or more, thereby offering interesting possibilities for formulation of lubricants with specific properties.

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Section: Configurational Analysismentioning

confidence: 82%

Rheological, thermodynamic, and structural studies of linear and branched alkanes under shear

Khare¹,

Pablo²,

Yethiraj³

1997

The Journal of Chemical Physics

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“…Similar potentials have been used in previous BD simulations with bead-bead repulsions. [15][16][17] Once the magnitudes and directions of all the repulsive forces acting on a given bead are known, they are divided by and added to the right-hand side of Eq. ͑1͒.…”

Section: Spring-spring Repulsionsmentioning

confidence: 99%

Brownian dynamics simulations of flexible polymers with spring–spring repulsions

Kumar

Larson

2001

The Journal of Chemical Physics

114

100

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We develop a method which incorporates spring-spring repulsions into Brownian dynamics simulations of flexible polymers. The distance of closest approach between two springs is computed, and a repulsive force is then applied based on this distance. Repulsive potentials of the exponential and power-law forms are considered. We demonstrate that our method is capable of accounting for excluded-volume effects in start-up of extensional flow. Equilibrium simulations indicate that spring-spring repulsions can be used to prevent the passage of two springs through each other, and thus maintain the topological integrity of polymer molecules. The method developed here is expected to be useful for simulating entanglement phenomena in both single and multichain systems.

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“…Our work differs substantially from that of Grassia & Hinch (1996) in that we consider birefringence, the effect of flow and the partitioning of the polymer stress into viscous and Brownian components which is crucial in the development of a constitutive equation for the polymer stress. Xu et al (1994) did examine bead-rod chains in steady shear and extensional flow, but they did not differentiate the Brownian from the viscous stress, nor did they determine the long-time chain relaxation scaling which is necessary to express results in terms of the chain Weissenberg number W i. Moreover, they did not attempt to calculate the optical properties of the chains, or determine universal scalings for the rheological material functions.…”

Section: Introductionmentioning

confidence: 99%

Dynamic simulation of freely draining flexible polymers in steady linear flows

Doyle¹,

Shaqfeh²,

Gast³

1997

J. Fluid Mech.

191

167

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We present a study of the rheological and optical behaviour of Kramers bead–rod chains in dilute solution using stochastic computer simulations. We consider two model linear flows, steady shear and uniaxial extensional flow, in which we calculate the non-Newtonian Brownian and viscous stress contribution of the polymers, their birefringence and a stress-optic coefficient. We have developed a computer algorithm to differentiate the Brownian from the viscous stress contributions which also avoids the order (δt)−1/2 noise associated with the Brownian forces. The strain or shear rate is made dimensionless with a molecular relaxation time determined by simulated relaxation of the birefringence and stress after a strong flow is applied. The characteristic long relaxation time obtained from the birefringence and stress are equivalent and shown to scale with N2 where N is the number of beads in the chain. For small shear or extension rates the viscous contribution to the effective viscosity is constant and scales as N. We obtain an analytic expression which explains the scaling and magnitude of this viscous contribution. In uniaxial extensional flow we find an increase in the extensional viscosity with the dimensionless flow strength up to a plateau value. Moreover, the Brownian stress also reaches a plateau and we develop an analytic expression which shows that the Brownian stress in an aligned bead–rod chain scales as N3. Using scaling arguments we show that the Brownian stress dominates in steady uniaxial extensional flow until large Wi, Wi ≈ 0.06N2, where Wi is the chain Weissenberg number. In shear flow the viscosity decays as Wi−1/2 and the first normal stress as Wi−4/3 at moderate Wi. We demonstrate that these scalings can be understood through a quasi-steady balance of shear forces with Brownian forces. For small Wi (in shear and uniaxial extensional flow) and for long times (in stress relaxation) the stress-optic law is found to be valid. We show that the rheology of the bead–rod chain can be qualitatively described by an equivalent FENE dumbbell for small Wi.

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Anisotropic friction and excluded volume effects in freely jointed bead–rod polymer chain models

Cited by 16 publications

References 22 publications

Rheological, thermodynamic, and structural studies of linear and branched alkanes under shear

Rheological, thermodynamic, and structural studies of linear and branched alkanes under shear

Brownian dynamics simulations of flexible polymers with spring–spring repulsions

Dynamic simulation of freely draining flexible polymers in steady linear flows

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