Characterization of the polycaprolactone melt crystallization: complementary optical microscopy, DSC, and AFM studies

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Kinetics

Background:

• Polycaprolactone (PCL) is a widely used biodegradable polyester.
• Understanding the initial stages of polymer crystallization is crucial for controlling material properties.
• Existing methods for studying polymer crystallization kinetics have limitations in sensitivity and timescale.

Purpose of the Study:

• To investigate the early stages of polycaprolactone (PCL) crystallization.
• To compare the sensitivity of different techniques in detecting the onset of crystallization.
• To critically evaluate the concept of induction time in polymer crystallization.

Main Methods:

• Differential Scanning Calorimetry (DSC) for thermal analysis.
• Polarized Optical Microscopy (POM) for visual observation.
• Rheology to assess viscoelastic changes.
• Atomic Force Microscopy (AFM) for high-resolution surface imaging.

Main Results:

• Atomic Force Microscopy (AFM) demonstrated the highest sensitivity in detecting the initial stages of PCL crystallization.
• Rheology was found to be the least sensitive technique for observing early crystallization events.
• Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM) yielded comparable results regarding crystallization onset.
• The observed differences underscore the influence of the observation scale on crystallization studies.

Conclusions:

• The sensitivity of crystallization detection is highly dependent on the technique and its observation scale.
• The concept of 'induction time' in polymer crystallization is ill-defined and requires explicit specification of the characterization method.
• AFM offers a promising approach for studying the very early stages of polymer crystallization, despite temporal limitations.