3D Orientation Imaging of Polymer Chains with Polarization-Controlled Coherent Raman Microscopy.

Area of Science:

• Materials Science
• Chemical Physics
• Microscopy

Background:

• Conventional 2D polarization imaging fails to capture the 3D molecular alignment in anisotropic materials.
• Understanding 3D molecular orientation is crucial for characterizing complex synthetic and biological materials.

Purpose of the Study:

• To develop and demonstrate a novel microscopy technique for imaging 3D molecular orientation with submicrometer resolution.
• To investigate the 3D molecular alignment of polyethylene (PE) chains within ring-banded spherulites.

Main Methods:

• Utilized polarization-controlled coherent anti-Stokes Raman scattering (CARS) microscopy.
• Acquired hyperspectral Raman data and converted it into 3D orientation images.
• Quantified 3D angles and order parameters of polymer chains.

Main Results:

• Successfully visualized the 3D angles of molecular orientations in a polyethylene film.
• Observed that PE chain azimuthal angles are perpendicular to the crystal growth direction.
• Detected limited-range oscillations in out-of-plane angles synchronous with ring banding, challenging existing crystal growth models.

Conclusions:

• The new CARS microscopy technique provides high-resolution, label-free, quantitative imaging of 3D molecular orientation.
• Findings challenge the prevailing crystal growth model of fully twisting lamellae.
• This method has the potential to become a standard tool for analyzing microscopic structures in diverse materials.