Three-Dimensional Molecular Orientation Imaging of a Semicrystalline Polymer Film under Shear Deformation

Abstract

The 3D molecular orientations of polymer chains are imaged and compared for a quiescent spherulite region and a shear-deformed region of a semicrystalline poly(ε-caprolactone) film. To acquire the images of 3D orientation, we used a newly developed hyperspectral imaging method based on the orthogonalpair polarization IR (OPPIR) analysis. Polymer chains in spherulites are azimuthally aligned perpendicular to the crystal growth direction and axially tilted from the film normal direction. By contrast, polymer chains in a sheared region are azimuthally aligned along the shear direction but axially tilted from the shear direction. The unexpected out-of-plane tilted orientation indicates that orientational relaxation followed shear deformation and occurred predominantly in the out-of-plane direction. Furthermore, incorporating peak deconvolution into the OPPIR analysis shows that the crystalline and amorphous chains are oriented aligned at different angles, possibly due to different orientational relaxation between the two chain configurations.

Super-Resolved 3D Mapping of Molecular Orientation Using Vibrational Techniques

“…Independently, Xu et al followed with two examples of concurrent 3D orientation application to IR imaging. 19,20 Moreover, we show that this method can be applied to diffraction-limited FT-IR and Raman imaging and even to super-resolved O-PTIR imaging. Due to the stationary experimental approach, no image distortion is visible and nanometer scale domains can be observed.…”

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

“…As opposed to those single Raman peak analyses, an algorithm based on two Raman peaks was theoretically proposed to determine the 3D orientation angles, 38 which is similar to the OPPIR method for IR imaging. 31,32 However, the proposed algorithm was based on the assumption that the polarizability tensors must have a single nonzero diagonal element, which is impractical for typical organic molecules, unfortunately.…”

“…30 The new method was experimentally demonstrated with a semicrystalline polymer film and the structural change induced by shear deformation. 31,32 However, the diffraction limit of IR microscopy is several micrometers, which is often not sufficient to resolve microscopic orientational variations.…”

“…Recently, a spectral analysis method, called the orthogonal-pair polarization IR (OPPIR), was proposed to determine 3D angles of molecular orientation by concurrently analyzing two orthogonal IR modes . The new method was experimentally demonstrated with a semicrystalline polymer film and the structural change induced by shear deformation. , However, the diffraction limit of IR microscopy is several micrometers, which is often not sufficient to resolve microscopic orientational variations.…”

“…Thus, analyzing a single Raman peak (e.g., the amide I peak) cannot yield the 3D orientation angles without a priori knowledge of the Raman tensor elements and the orientational broadening, , which are not trivial to measure independently at the exact location of the sample. As opposed to those single Raman peak analyses, an algorithm based on two Raman peaks was theoretically proposed to determine the 3D orientation angles, which is similar to the OPPIR method for IR imaging. , However, the proposed algorithm was based on the assumption that the polarizability tensors must have a single nonzero diagonal element, which is impractical for typical organic molecules, unfortunately.…”