A molecular model for cohesive slip at polymer melt/solid interfaces

Area of Science:

• Polymer Physics
• Materials Science
• Rheology

Background:

• Wall slip is a critical phenomenon in polymer processing, affecting melt flow and product quality.
• Existing models often lack the molecular detail to fully capture slip mechanisms.
• Understanding near-wall polymer dynamics is essential for predicting macroscopic flow behavior.

Purpose of the Study:

• To develop a quantitative molecular model for predicting wall slip in polymers.
• To elucidate the role of adsorbed polymer chains and their disentanglement in slip.
• To establish a predictive relationship between molecular parameters, extruder geometry, and stick-slip behavior.

Main Methods:

• Formulation of a nonlinear equation of motion for the near-wall boundary layer, incorporating chain dynamics (convection, retraction, constraint release, thermal fluctuations).
• Coupling of adsorbed chain dynamics with bulk polymer dynamics via constraint release mechanism.
• Development of a closed system of equations for the bulk and boundary layer, solved to yield a stick-slip law.

Main Results:

• The proposed model quantitatively predicts wall slip based on molecular parameters and extruder geometry.
• The model accounts for various grafting regimes, including those with significant inter-chain interactions.
• Model predictions demonstrate good agreement with existing experimental observations.

Conclusions:

• The molecular model provides a mechanistic understanding of wall slip through polymer chain disentanglement.
• The model is predictive and relies on measurable or independently obtainable parameters.
• This approach offers a pathway to optimize polymer processing by controlling molecular and geometric factors affecting slip.