Imaging 3D molecular orientation by orthogonal-pair polarization IR microscopy

Area of Science:

• Materials Science
• Spectroscopy
• Polymer Science

Background:

• Anisotropic molecular alignment is common but challenging to image in 3D.
• Existing polarization imaging methods are limited to 2D projections of molecular orientation.
• Understanding 3D molecular structure is crucial for heterogeneous materials.

Purpose of the Study:

• To develop and demonstrate a method for mapping 3D molecular orientation angles.
• To analyze the local orientational distribution of polymer chains in a semicrystalline film.
• To overcome the limitations of conventional 2D polarization imaging.

Main Methods:

• Developed a novel algorithm to convert polarization-controlled infrared hyperspectral data into 3D orientation images.
• Utilized the orthogonal-pair polarization IR (OPPIR) method, processing orthogonal IR transition-dipole modes concurrently.
• Applied OPPIR to map 3D orientation angles and order parameters in a poly(ε-caprolactone) film.

Main Results:

• Successfully mapped the 3D orientation angles of polymer chains.
• Determined the order parameter of the local orientational distribution.
• Observed specific alignment patterns: azimuthal alignment perpendicular to the spherulite radial direction and axial tilt from the film normal.

Conclusions:

• The OPPIR method provides unprecedented insights into 3D molecular alignments.
• This technique is valuable for understanding the molecular-level structure of anisotropic and heterogeneous materials.
• The findings advance the characterization of polymer chain organization in semicrystalline structures.