Mechanisms of Directional Polymer Crystallization

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Engineering

Background:

• Zone annealing, a directional crystallization technique, is adapted for crystalline polymers.
• Precise control over lamellar orientation and thickness in semicrystalline polymers is achievable through directional solidification.
• Previous theories suggested a steady-state crystal growth rate equal to sample velocity and directional crystallization below a critical velocity.

Purpose of the Study:

• To examine conjectures on polymer zone annealing by Lovinger and Gryte.
• To analyze the relationship between sample velocity and polymer crystallization mechanisms.
• To investigate the transitional region of directional crystallization in polymers.

Main Methods:

• Zone annealing of poly(ethylene oxide).
• Analysis using small-angle X-ray scattering (SAXS).
• Differential scanning calorimetry (DSC) and cross-polarized optical microscopy.

Main Results:

• Long period data validated the steady-state growth rate ansatz.
• Herman's orientation function analysis revealed a transitional region around a critical velocity (vcrit).
• Below vcrit, directional crystallization was achieved; above vcrit, isotropic crystallization dominated.

Conclusions:

• The study validates the steady-state assumption for polymer zone annealing.
• A critical velocity governs the transition between directional and isotropic crystallization mechanisms.
• Zone annealing offers a method for controlling polymer microstructure through directional solidification.