Theory of Flow-Induced Fibril Formation in Polymer Solutions

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Flow-induced crystallization is vital for polymer processing.
• Understanding the formation of polymer fibrils (shish) is key to controlling material properties.
• Previous models did not fully explain fibril stability and dimensions.

Purpose of the Study:

• To develop a theoretical framework for the formation of polymer core fibrils (shish) via flow-induced crystallization.
• To explain the stable diameter and length of these fibrils using the concept of cumulative strain.
• To predict the influence of undercooling, annealing, and volume strain on fibril characteristics and melting behavior.

Main Methods:

• Theoretical treatment of cumulative strain in polymer crystallization.
• Modeling nucleation and growth of embryonic fibrils.
• Analysis of surface stress and volume strain effects on crystallites.
• Calculation of melting behavior based on fibril structure and strain.

Main Results:

• A stable fibril diameter and characteristic length are predicted based on cumulative strain.
• The theory aligns with experimental data regarding the dependence of fibril dimensions on undercooling.
• Lattice expansion due to volume strain and melting behavior are accurately reproduced.
• Polyethylene fibril crystallinity versus temperature data is explained.

Conclusions:

• The core fibril is a series of extended-chain crystallites with specific end structures and lattice strain.
• Cumulative strain theory provides a robust explanation for flow-induced fibril formation and stability.
• The model successfully predicts key material properties and offers insights into annealing effects.