Structural properties of hyperbranched polymers in the melt under shear via nonequilibrium molecular dynamics simulation

Le, Tu C.; Todd, B. D.; Daivis, Peter J.; Uhlherr, Alfred

doi:10.1063/1.3077006

Cited by 26 publications

(32 citation statements)

References 35 publications

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“…[27] In contrast to the extensive research into dendrimers, hyperbranched polymers have received much less attention. Richards et al [28] and Buzza [29] studied the properties of hyperbranched polymer using information from theoretical molecular weight distributions, and these have also been several simulation studies of relatively low-molecular-weight hyperbranched polymers under various conditions, [30][31][32][33][34][35][36] which have been subsequently extended to higher degrees of polymerization. [37,38] More recently, a model called random branching theory was developed to describe randomly hyperbranched polymers.…”

Section: Introductionmentioning

confidence: 99%

Describing the Structure of a Randomly Hyperbranched Polymer

Konkolewicz

Gray‐Weale

Perrier

2010

Macro Theory & Simulations

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This paper describes random branching theory, a model for the solution structure of hyperbranched polymers. In this model, the hyperbranched polymer is assumed to be composed of units whose structure is simpler than the resulting polymer. These simple units can have any structure of chemical functionality, from monomers to linear chains or spherical particles. This paper outlines how this theory is constructed, describes the underlying assumptions and parameters, and summarizes the most basic form. It is shown how variations in the parameters change the behavior of the model, and described how to fit an experimental data series. This demonstrates how the model can be used to fit other data series, and how it can be used as a test for whether a polymer is randomly hyperbranched.magnified image

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Section: Introductionmentioning

confidence: 99%

Describing the Structure of a Randomly Hyperbranched Polymer

Konkolewicz

Gray‐Weale

Perrier

2010

Macro Theory & Simulations

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“…Details of these potentials can be found in our previous paper. 2 In the remainder of this paper, all quantities are expressed in terms of site reduced units in which the reduction parameters are the Lennard-Jones interaction parameters and and the mass, m i␣ , of bead ␣ in molecule i. The reduced temperature is given by T ‫ء‬ = k B T / where k B is the Boltzmann constant, the density is given by ‫ء‬ = 3 , the pressure tensor by P ‫ء‬ = P 3 / , and strain rate by ␥ ‫ء‬ = ͑m i␣ 2 / ͒ 1/2 ␥ .…”

Section: Methodsmentioning

confidence: 99%

“…Such ordering is consistent with the prolate ellipsoid molecular shape characterized by the eigenvalues of the gyration tensor as discussed in our previous paper. 2 The order parameter of the molecular alignment tensor is actually a measure of the ordering of the anisotropy of the directors of the molecules. In all cases, the order parameter remains constant at low strain rates and increases in high strain rate regions.…”

Section: B Flow Birefringencementioning

confidence: 99%

The effect of interbranch spacing on structural and rheological properties of hyperbranched polymer melts

Todd

Daivis

et al. 2009

The Journal of Chemical Physics

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Nonequilibrium molecular dynamics simulations were performed for a family of hyperbranched polymers of the same molecular weight but with different chain lengths between branches. Microscopic structural properties including mean squared radius of gyration, distribution of beads from the center of mass and from the core and the interpenetration function of these systems were characterized. A relationship between the zero shear rate mean squared radius of gyration and the Wiener index was established. The molecular and bond alignment tensors were analyzed to characterize the flow birefringence of these hyperbranched polymers. The melt rheology was also studied and the crossover from the Newtonian to non-Newtonian behavior was captured for all polymer fluids in the considered range of strain rates. Rheological properties including the shear viscosity and normal stress coefficients obtained from constant pressure simulations were found to be the same as those from constant volume simulations except at high strain rates due to shear dilatancy. A linear dependence of zero shear rate viscosities on the number of spacer units was found. The stress optical rule was shown to be valid at low strain rates with the stress optical coefficient of approximately 3.2 independent of the topologies of polymers.

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“…14,25,27,32,63,64 However, they clearly exhibited an increased value of R g 2 at high shear rates. 14,25,27,32,63,64 However, they clearly exhibited an increased value of R g 2 at high shear rates.…”

Section: Molecular Dimensionmentioning

confidence: 97%

Molecular structural property and potential energy dependence on nonequilibrium-thermodynamic state point of liquid n-hexadecane under shear

Tseng¹,

Chang

2011

The Journal of Chemical Physics

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Extensive computer experiments have been conducted in order to shed light on the macroscopic shear flow behavior of liquid n-hexadecane fluid under isobaric-isothermal conditions through the nonequilibrium molecular dynamic methodology. With respect to shear rates, the accompanying variations in structural properties of the fluid span the microscopic range of understanding from the intrinsic to extrinsic characteristics. As drawn from the average value of bond length and bond angle, the distribution of dihedral angle, and the radius distribution function of intramolecular and intermolecular van der Waals distances, these intrinsic structures change with hardness, except in the situation of extreme shear rates. The shear-induced variation of thermodynamic state curve along with the shear rate studied is shown to consist of both the quasiequilibrium state plateau and the nonequilibrium-thermodynamic state slope. Significantly, the occurrence of nonequilibrium-thermodynamic state behavior is attributed to variations in molecular potential energies, which include bond stretching, bond bending, bond torsion, and intra- and intermolecular van der Waals interactions. To unfold the physical representation of extrinsic structural deformation, under the aggressive influence of a shear flow field, the molecular dimension and appearance can be directly described via the squared radius of gyration and the sphericity angle, R(g)(2) and ϕ, respectively. In addition, a specific orientational order S(x) defines the alignment of the molecules with the flow direction of the x-axis. As a result, at low shear rates, the overall molecules are slightly stretched and shaped in a manner that is increasingly ellipsoidal. Simultaneously, there is an obvious enhancement in the order. In contrast to high shear rates, the molecules spontaneously shrink themselves with a decreased value of R(g)(2), while their shape and order barely vary with an infinite value of ϕ and S(x). It is important to note that under different temperatures and pressures, these three parameters are integrated within a molecular description in response to thermodynamic state variable of density and rheological material function of shear viscosity.

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Structural properties of hyperbranched polymers in the melt under shear via nonequilibrium molecular dynamics simulation

Cited by 26 publications

References 35 publications

Describing the Structure of a Randomly Hyperbranched Polymer

Describing the Structure of a Randomly Hyperbranched Polymer

The effect of interbranch spacing on structural and rheological properties of hyperbranched polymer melts

Molecular structural property and potential energy dependence on nonequilibrium-thermodynamic state point of liquid n-hexadecane under shear

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