Shear response of polyelectrolytes in water

Area of Science:

• Polymer Physics
• Rheology
• Computational Chemistry

Background:

• The relationship between microscopic conformational dynamics of polyelectrolytes and their macroscopic rheological properties is not fully understood.
• Polyelectrolytes in solution exhibit distinct behaviors under shear stress.

Purpose of the Study:

• To investigate the conformational dynamics of polyelectrolytes under shear using molecular dynamics simulations.
• To correlate microscopic chain movements with macroscopic rheological characteristics.

Main Methods:

• Large-scale, fully atomistic molecular dynamics simulations.
• Analysis of aqueous solutions of fully sulfonated polystyrene polyelectrolytes under shear.

Main Results:

• Under shear, polyelectrolyte chains display diverse conformational fluctuations, deviating from their quiescent extended state.
• Chains fold transversely, leading to characteristic tumbling dynamics.
• The tumbling time (τ_{r}) exhibits a scaling relationship with the shear rate (γ̇) as γ̇^{-2/3}.

Conclusions:

• The observed tumbling dynamics are a fundamental aspect of polyelectrolyte behavior under shear.
• This scaling behavior is consistent with experimental observations in biomolecules, suggesting a universal mechanism.
• The findings provide insights into the microscopic origins of rheological properties in polyelectrolyte solutions.