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

Abstract

Despite the ubiquity of three-dimensional (3D) anisotropic materials, their 3D molecular alignment cannot be measured using conventional two-dimensional (2D) polarization imaging. Here, we present images of the 3D angles of molecular orientations with submicrometer spatial resolution acquired through polarization-controlled coherent anti-Stokes Raman scattering microscopy. The hyperspectral Raman data of a polyethylene (PE) film were converted into images, showing the polymer chains' 3D angles and order parameters. The 3D orientation images of PE chains in ring-banded spherulites show that the azimuthal angles of the chains are perpendicular to the crystal growth direction, while the out-of-plane angles display limited-range oscillations synchronous with ring banding. The prevailing crystal growth model of fully twisting lamellae is inconsistent with the observed restricted oscillations of the out-of-plane direction, which are unobservable through conventional 2D projected imaging. This high-resolution, label-free, quantitative imaging of 3D molecular orientation can become a standard measurement tool for the microscopic structures of complex synthetic and biological materials.

Computational approach for structure generation of anisotropic particles (CASGAP) with targeted distributions of particle design and orientational order

“…In particular, we formalize the distribution of orientational order by using the von Mises-Fisher distribution which has rarely been used in the context of soft materials. 44,45 We demonstrate that for some of these parameters, in place of a distribution, a more complex spatial fieldbased description can also be imposed to add spatial correlations, aiding in the modeling of sophisticated or hierarchical structures. We tackle unique challenges that one faces with non-spherical particles that are not an issue when dealing with spherical particles, including determining overlap between two particles which can be highly specific to the shape of the individual particles.…”