Effect of Molecular Shape on Rheological Properties in Molecular Dynamics Simulation of Star, H, Comb, and Linear Polymer Melts

Wall slip is one of the most important characteristics of polymer melts’ elasticity behaviours as well as the most significant factor which affects the flow of polymer melts. Based on the traditional Mooney method, through a double-barrel capillary rheometer, the relationship between velocities of wall slip, shear stress, shear rate, diameters of dies, and temperature of polypropylene (PP), high-density polyethylene (HDPE), polystyrene (PS), and polymethylmethacrylate (PMMA) is explored. The results indicate that the velocities of the wall slip of PP and HDPE increase apparently with shear stress and slightly with temperature. Meanwhile, the rise of temperature results in the decrease of critical shear stress. The wall-slip velocities of PS and PMMA are negative which means that the Mooney method based on the adsorption–desorption mechanism has determinate limitation to calculate the wall-slip velocity. Based on the entanglement–disentanglement mechanism, a new wall-slip model is built. With the new model, the calculation values of velocity of PP and HDPE correspond to the experimental values very well and the velocities of PS and PMMA are positive. The velocities of PS and PMMA increase obviously with the rise of shear stress. The rise of temperature results in the increase of velocity and decrease of critical shear stress. Then, the molecular dynamics simulation is used to investigate the combining energy between four polymer melts and the inside wall. The results show that at the given temperature and pressure, the molecules of PS and PMMA combine with atoms of the wall more tightly than those of PP and HDPE which means when wall slip occurs, the molecules of PS and PMMA near the wall will adsorb to the surface of the wall. However, those of PP and HDPE will be easy to slip. Therefore, the wall-slip mechanism of PP and HDPE is the adsorption–desorption mechanism, and that of PS and PMMA is the entanglement–disentanglement mechanism. According to the different wall-slip mechanisms of four polymers, an all-sided calculation method of wall-slip velocity is raised which consummates the theory of wall slip of polymer melts.

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Segregated structures of ring polymer melts near the surface: a molecular dynamics simulation study

Soft Matter ◽

10.1039/c5sm01097g ◽

2015 ◽

Vol 11 (30) ◽

pp. 6018-6028 ◽

Cited By ~ 13

Author(s):

Eunsang Lee ◽

YounJoon Jung

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Simulation Study ◽

Polymer Melts ◽

Dynamics Simulation ◽

Ring Polymer ◽

Segregated Structure

A ring polymer in a melt under confinement shows a very compact and segregated structure.

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Multiple time step nonequilibrium molecular dynamics simulation of the rheological properties of liquid n‐decane

The Journal of Chemical Physics ◽

10.1063/1.470896 ◽

1996 ◽

Vol 104 (1) ◽

pp. 255-262 ◽

Cited By ~ 79

Author(s):

S. T. Cui ◽

P. T. Cummings ◽

H. D. Cochran

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Rheological Properties ◽

Dynamics Simulation ◽

Nonequilibrium Molecular Dynamics ◽

Multiple Time ◽

Time Step ◽

Multiple Time Step ◽

Nonequilibrium Molecular Dynamics Simulation

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Prediction of Thermal Conductivity and Shear Viscosity of Water-Cu Nanofluids Using Equilibrium Molecular Dynamics

Volume 8C: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-63558 ◽

2013 ◽

Cited By ~ 1

Author(s):

Tolga Akıner ◽

Hakan Ertürk ◽

Kunt Atalık

Keyword(s):

Experimental Data ◽

Thermal Conductivity ◽

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Rheological Properties ◽

Shear Viscosity ◽

Effective Properties ◽

Dynamics Simulation ◽

Modeling Tools ◽

Macroscopic Modeling

Nanofluids are new class of fluids which can be used for many engineering applications due to their enhanced thermal properties. The macroscopic modeling tools used for flow simulations usually rely on effective thermal and rheological properties of the nanofluids that can be predicted through various effective medium theories. As these theories significantly under-predict, using correlations based on experimental data is considered as the only reliable means for prediction of these effective properties. However, the behavior might change significantly once the particle material or base fluid change due to different particle fluid interactions in the molecular level. One of the most promising means of modeling effective properties of the nanofluids is the molecular dynamics simulations where all the intermolecular effects can be modeled. This study investigates equilibrium molecular dynamics simulation of the water-Cu nanofluids to predict the thermal and rheological properties. The molecular dynamics simulation is carried out to achieve a thermodynamic equilibrium, based on a state that is defined by targeted thermodynamic properties of the system. The Green-Kubo method is used to predict the thermal conductivity and viscosity of the system. The study considers the use of different combining rules such as Lorentz-Berthelot and sixth-power rules for defining the inter-atomic potentials for water modeled by SPC/E and nanoparticles modeled by Lennard-Jones potential. The predicted effective properties that are thermal conductivity and shear viscosity are then compared with experimental data from literature. The predicted transport properties at different temperatures and particle concentrations are compared to experimental data from literature for model validation.

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