Nonlinear rheometry of entangled polymeric rings and ring-linear blends

Area of Science:

• Polymer Physics
• Rheology
• Materials Science

Background:

• Understanding the nonlinear rheological behavior of entangled polymers is crucial for material design.
• Ring polymers, lacking chain ends, exhibit distinct topological properties compared to linear polymers.
• Previous studies suggest differences in rheological response between ring and linear polymer systems.

Purpose of the Study:

• To provide a comprehensive experimental rheological dataset for entangled ring polystyrenes and their blends with linear chains.
• To investigate nonlinear shear and elongational flow behavior as a function of shear rate and molecular parameters.
• To elucidate the role of topological differences (rings vs. linear) in rheological response and mechanical reinforcement.

Main Methods:

• Experimental rheology measurements including shear stress growth coefficient, steady-state shear viscosity, and normal stress differences.
• Nonlinear shear and elongational flow tests across an extended parameter range.
• Analysis of data as a function of shear rate, molar mass, and blend composition.

Main Results:

• Pure rings lack clear transient shear undershoot, unlike linear polymers and ring-linear blends.
• The second normal stress difference (N2) for rings is significantly larger in magnitude than for linear polymers with similar entanglement numbers.
• Ring-linear blends show significant viscosity enhancement in elongation due to ring-linear threading and interlocking, leading to mechanical reinforcement.

Conclusions:

• Entangled ring polymers possess distinct nonlinear rheological characteristics compared to linear polymers.
• The interlocking nature of ring polymers plays a critical role in their rheological response and reinforcing effect in blends.
• Experimental data align with predictions from shear slit models and molecular dynamics simulations, validating theoretical frameworks.