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Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions
Published on: April 19, 2018
Rheological and structural studies of linear polyethylene melts under planar elongational flow using nonequilibrium
C Baig1, B J Edwards, D J Keffer
1Department of Chemical Engineering, University of Tennessee, Knoxville, Tennessee 37996-2200, USA.
The Journal of Chemical Physics
|March 4, 2006
Summary
Polyethylene melts exhibit tension-thinning behavior in elongational flow, with viscosity following a power law. Molecular dynamics simulations reveal how chain length and flow rate influence rheological and structural properties.
Area of Science:
- Polymer Physics
- Materials Science
- Computational Chemistry
Background:
- Understanding the rheological and structural properties of polymer melts under flow is crucial for material processing and design.
- Polyethylene, a widely used polymer, exhibits complex behavior under deformation.
Purpose of the Study:
- To investigate the rheological and structural properties of polyethylene liquids under planar elongational flow.
- To analyze the influence of chain length and elongation rate on viscosity, pressure, and molecular conformation.
Main Methods:
- Non-equilibrium molecular dynamics simulations were employed.
- Simulations were performed on three polyethylene liquids (C50H102, C78H158, C128H258) under planar elongational flow.
Main Results:
- All polyethylene melts displayed tension-thinning behavior, with elongational viscosities following a power law (eta ~ epsilon^b).
- The exponent 'b' was approximately -0.4, varying slightly with chain length for eta1 but independent for eta2.
- Intermolecular and intramolecular Lennard-Jones (LJ) energies, bond stretching, bending, and torsional modes contributed differently to viscosity.
- Hydrostatic pressure showed a minimum at a specific elongation rate, which increased with chain length.
- Conformation tensor analysis indicated increased chain extension with higher elongation rates and longer chains.
Conclusions:
- Polyethylene melts exhibit shear-thinning behavior governed by a power law under elongational flow.
- Molecular dynamics simulations provide insights into the microscopic origins of macroscopic rheological properties.
- The relationship between stress and conformation tensor may not be universally linear for arbitrary flows.
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